HERBOLOGIA - anubih

UDK 63/66 ISSN 1840-0809 

HERBOLOGIA 

An International Journal on Weed Research and Control 

Vol. 7, No. 1, April 2006

Issued by: The Academy of Sciences and Arts of Bosnia and Herzegovina 

and The Weed Science Society of Bosnia and Herzegovina 

Editorial Board 

Paolo Barberi (Italy) 

Vladimir Borona (Ukraine) 

Daniela Chodova (Czech Republic) 

Mirha ðikić (B&H) 

Aniko Farkas (Hungary) 

Azra Hadžić (B&H) 

Senka Milanova (Bulgaria) 

Ševal Muminović (BiH) 

Shamsher S. Narwal (India) 

Zvonimir Ostojić (Croatia) 

Danijela Petrović (B&H) 

Marko Skoko (B&H) 

Lidija Stefanović (S&M) 

Taib Šarić (B&H) 

Dubravka Šoljan B&H) 

Editor-in-Chief: Prof. Dr. Taib Šarić 

Technical Editor: Dr. Mirha ðikić 

Address of the Editorial Board and Administration 

Herbološko društvo BiH (Poljoprivredni fakultet) 

Sarajevo, Zmaja od Bosne 8, Bosna i Hercegovina 

Phone: ++387 33 653 033, Fax: ++387 33 667 429 

E-mail: tsaric@bih.net.ba 

Published four times a year 

The price of a copy of the Journal: 15 € 

Printed by 

Štamparija GARMOND GRAPHIC, Sarajevo

CONTENTS 

Page 

1. A Jubilee……………………………………………………………...1 

2. V. D. Mircov, I. ðalović, Z. Brocić: Results of weed control in 

field potatoes…………………………………………………………3 

3. Anikó Farkas: Soil management and tillage possibilities in weed 

control………………………………………………………………..9 

4. B. Konstantinović, Maja Meseldžija, Dragana Šunjka: Resistance 

study of Amaranthus retroflexus L. species population to the 

herbicide imazethapyr……………………………………………….31 

5. Tsvetanka Dimitrova, Senka Milanova: Influence of the adjuvant 

Desh on the efficacy and selectivity of imazamox 40 a.i.l -1 (Pulsar 40) 

in three perennial legume crops……………………………………..41 

6. Z. Pacanoski: Herbicide-resistant crops - advantages and risks…...47 

7. T. Šarić, I. ðalović: Production of allergenic pollen by ragweed 

(Ambrosia artemisiifolia L.) is increased in CO 2 -enriched 

atmospheres…………………………………………………………59 

8. G. Malidža, V. Janjić, I. ðalović: Genetically modified 

herbicide–tolerant crops – state and perspectives............................67 

Instruction to Authors in Herbologia………………………………….94

Herbologia Vol. 7, No.1, 2006. 

A Jubilee 

50 years of Prof. Taib Saric’s work in science and higher education 

Professor Taib Saric, Editor of Herbologia, this spring 

celebrates 50 years of his fruitful and devoted work in agricultural 

science and university education. His contribution to agricultural 

profession, science and education has been immense. Although 

retired, as professor emeritus he continues to give his significant 

contribution, particularly in guiding M.S. and Ph.D. candidates, and 

in editting the International Journal for Weed Research and Control 

Herbologia. 

By this modest article we wish to thank our respectable and prominent 

Professor for the tremendous work he has done during five decades and to wish 

him good health, to stay further with us for many years on the benefit of agricultural 

science and practice. 

Short curriculum vitae 

Profesor Taib Saric was born in Capljina (Bosnia and Herzegovina) in 

1934. He took his B.S., M.S. and Ph.D. degrees in agronomy from the University of 

Sarajevo. He studied weed science and agroecology at post-master′s study at Kansas 

State University, Manhattan, Ks. and Bucknell University in Pennsylvania, U.S.A., 

and post-doctoral study in weed science at the Wageningen Agricultural University 

in the Netherlands. He joined the Indian Agricultural Research Institute in New 

Delhi for two years performing research on subtropical field crops. 

From 1962 he has been working with the Faculty of Agriculture of the 

University of Sarajevo as an assistant, assistant professor, associate professor, full 

professor and professor emeritus in agroecology, soil management, weed science, 

and environmental protection, participating in education of 44 generations of 

students. 

In the last 30 years he was Editor-in-Chief of three scientific journals, the 

last of them being Herbologia. He published more than 100 research papers, about 

600 professional articles, and 24 books (with updated editions a total of 44 books) 

on soil management, agroecology, weed science, and environmental protection. His 

book Soil Management (four editions) was the major textbook for students of 

agronomy in Yugoslavia. His Weed Atlas (five editions), with nomenclature in nine 

languages, has been used in about 30 countries all over the world. 

He was one of the founders of the Weed Science Society of Yugoslavia (in 

Sarajevo, 1973) and was its president. He was one of the founders of the European 

Weed Research Society (EWRS, in Paris, 1975) and a member of its Scientific 

Committee and Educational Committee. During 30 years he was National 

Representative of Yugoslavia, and latter on of Bosnia and Herzegovina, to the 

EWRS. He led the foundation of the Weed Science Society of Bosnia and 

Herzegovina.

A Jubilee 

In 1977 at the Faculty of Agriculture in Sarajevo he founded the first 

postgraduate study in weed science with teachers from Yugoslavia, Switzerland, 

Italy, etc. 

He presented numerous papers with results of his research at Symposia and 

Congresses held in Uppsala, Moscow, Warshaw, Leipzig, Brno, Bratislava, 

Keszhtely (Hungary), Poznan, Brighton, Gent, Sydney, etc. He was chairperson at 

the EWRS Symposia in Uppsala, Paris and Lisbon. As a guest of the Indian 

Government he delivered the invited introductory lecture on the methods of 

promotion of field crop production on the 63 rd Indian Science Congress, Section for 

Agriculture, in Vishakhapatnam in 1976. After that, he lectured at graduate studies 

at Agricultural Universities in New Delhi, Hyderabad and Bangalore. 

He was a foreign peer-reviewer of several Ph.D. thesis at foreign 

universities and in electing full professors at them. 

For his rich scientific opus and prolific profesional publications Prof. Saric 

was conferred the State Award „Veselin Maslesa“. He was twice nominated a 

laureate of the World Food Prize (known informally as the Nobel Prize for Food 

and Agriculture). He is a member of the Academy of Sciences and Arts of Bosnia 

and Herzegovina. 

Contribution to weed science 

In the course of 50 years, Professor Saric greatly contributed to weed 

science through his research, his numerous publications (papers and books) and 

through educating many generations of undergraduate, postgraduate and doctoral 

students. His research was particularly devoted to spreading of new, invasive weed 

species, various ways of weed control, herbicide testing and application, and cropweed 

allelopathy. In studying the weed flora of Bosnia and Herzegovina he 

continued the research started by Komsa and Vaskovic in the first decades of the 

20th century. He pioneered the introduction of herbicides in Bosnia. He was one of 

the pioneers of weed science in Yugoslavia. He took part in founding and work of 

the EWRS. He was among the organizers of the most of national and international 

Weed Symposia and Congresses held in Yugoslavia. 

His great knowledge and very rich experience Prof. Saric has all the time 

readily transfered to us, his students and coworkers, to other agronomists, and to 

farmers. He will for long time remain an unparalleled coryphaeus of our weed 

science, as well as the science of soil management and agroecology. 

Prof. S. Muminovic 

2

Herbologia Vol. 7, No.1, 2006. 

RESULTS OF WEED CONTROL IN FIELD POTATOES 

Vlad Dragoslav Mircov 1 , Ivica ðalović 2 , Zoran Brocić 3 

1 University of Agricultural Sciences and 

Veterinary Medicine of Banat – Timisoara, Romania 

2 Faculty of Agronomy – Cacak, Serbia and Montenegro 

3 Faculty of Agriculturae, Belgrade – Zemun, Serbia and Montenegro 

Abstract 

Weed competition can reduce yield and potato quality, affecting tuber 

size, weight, and quantity. In this research paper it was compared the 

efficacy of 10 herbicide treatments for controlling prostrate pigweed, kochia, 

and Russian thistle in a low organic coarse–textured soil and to determine 

their effect on marketable potato yields. 

Study results emphasize the need for good weed control for optimum 

potato yields. Metribuzin applied alone or in combination with metolachlor, 

pendimethalin, or trifluralin plus EPTC gave excellent broadleaf weed 

control and the highest marketable potato yields. 

Key words: weeds, weed control, field potatoes. 

Introduction 

Weed competition can reduce yield (VanGessel and Renner, 1990) and 

potato quality (VanGessel and Renner, 1990), affecting tuber size, weight, 

and quantity (Nelson and Thoreson, 1981; Wall and Friesen, 1990a, Rosales– 

Robles et. al., 1999). Weeds interfere with harvest, causing more potatoes to 

be left in the field and increasing mechanical injury (VanGessel and Renner, 

1990). If a mixed population of annual weeds is allowed to compete with 

potatoes all season, each 10% increase in dry weed biomass causes a 12% 

decrease in tuber yield. One redroot pigweed (Amaranthus retroflexus L.) or 

barnyardgrass [Echinochloa crus–galli (L.) Beauv.] per meter of row reduced 

marketable tuber yield 19 to 33% (VanGessel and Renner, 1990; 

Baziramakenga and Leroux, 1998). 

The critical period for weed removal in potatoes is about 4 to 6 weeks 

after planting. Weeds emerging 4 weeks after planting are suppressed by crop 

growth (Thakral et. al., 1989). These weeds may not reduce tuber yield 

through competition, but can interfere with harvest operations. 

Mechanical cultivation does not remove weeds within the row and may 

damage potato plants and reduce yields (Nelson and Giles, 1989). Herbicides 

can reduce the number of cultivations required and enhance weed control 

particularly during the early season before hilling. Many herbicides are

V.D. Mircov et al. 

approved for use on potatoes grown on medium– and fine–textured, high– 

organic soils. Relatively little information is available regarding the 

effectiveness and safety of herbicides for potatoes grown in low–organic 

matter, coarse–textured soils. 

The objectives of this research were to compare the efficacy of 10 

herbicide treatments for controlling prostrate pigweed, kochia, and Russian 

thistle in a low organic, coarse–textured soil and to determine their effect on 

marketable potato yields. 

Materials and methods 

Field trials were conducted over a three–year period from 2002 to 

2004 at the experimental station University of Agricultural Sciences and 

Veterinary Medicine of Banat – Timisoara in Romania. The soil was a 

chernozem. Soils were fertilized according to Timisoara recommendations 

based on soil tests (N=0.219 mg/100 g soil, P 2 O 5 =21.4 mg/100 g and 

K 2 O=31.6 mg/100g soil). Fields were plowed, disked, leveled, and hilled 

prior to planting. 

A randomized complete block design with three replications was used. 

The distance between rows was 75 cm and the distance between the plants in 

a row was 33 cm, density being 40.000 plants per hectare. The seed of class 

A was used. Potato sowing on April 14, 2002 (cv. Desiree); April 20, 2003 

(cv. Adora); and April 19, 2004 (cv. Adora). 

Prostrate pigweed, kochia, and Russian thistle were broadcast seeded at 

a rate of 1.0 kg/ha –1 each and harrow incorporated prior to planting. The 

chemical designations for the proprietary herbicides evaluated were: 

Common name 

metolachlor 

EPTC 

fluorochloridone 

metribuzin 

pendimethalin 

trifluralin 

Trade name 

Dual 

Eptam 

Racer (proposed) 

Sencor 

Prowl 

Treflan 

Preplant incorporated (PPI) treatments were applied April 14, 2002; 

April 16, 2003; and April 19, 2004 and immediately incorporated to a depth 

of 4 to 5 cm with a tractor–driven rotary tiller. Preemergence (PRE) 

treatments were applied April 30, 2002; April 24, 2003; and April 22, 2004 

and immediately incorporated with 1–2 cm of sprinkler–applied water. 

Visual evaluations of crop injury and weed control were made July 17, 

2002; July 21, 2003; and June 23, 2004. Weed control was based on a 0–to– 

4

Results of weed control in field potatoes 

100% scale, where 0 = no control and 100 = no living weeds. Infestations 

were light throughout the experimental area for all three weeds. Weeds were 

hoed from the weed–free controls as needed, beginning one month after 

planting and continuing through August. 

Potatoes were mechanically harvested with a tractor–driven potato 

digger on October 2, 2002; September 22, 2003; and September 19, 2004 

from 1,5 m of the center two rows of each plot. The harvested potatoes were 

graded to separate marketable tubers. 

Tubers that were diseased, less than 28/55 mm were discarded. 

Previous research indicates that specific gravity is independent of weed 

density, so specific gravity was not measured. Values for weed control and 

marketable yield were subjected to analysis of variance, and treatment means 

were separated by Fisher’s LSD test at the 5% significance level. There was 

no significant year–by–treatment interaction, so data were combined for all 

three years. 

Results and discussion 

Fluorochloridone was the only treatment that injured potato plants 

during all three years (data not shown). At both rates, potato plants exhibited 

chlorosis along leaf veins, and plants were slightly reduced in size. As the 

season progressed, injury symptoms diminished, and there appeared to be no 

difference in foliar growth among all treatments at harvest. 

All herbicide treatments controlled 100% of prostrate pigweed (table 

1). Trifluralin, in combination with metolachlor or with EPTC, controlled 

less than 95% of kochia (an average of 89% and 88%, respectively). Adding 

metribuzin to trifluralin plus EPTC increased control to 100%. Pendimethalin 

alone or in combination with EPTC controlled less than 75% of Russian 

thistle. 

Adding metribuzin to pendimethalin increased Russian thistle control 

to 95%. All other treatments controlled 90% or more of Russian thistle. The 

unweeded control yielded the least marketable potatoes of all treatments 

(table 1) and produced 61% less than the weed–free control. The greatest 

potato tuber yields were noted in plots treated with metribuzin alone or in 

combination with metolachlor or pendimethalin. Pendimethalin alone and in 

combination with EPTC failed to control Russian thistle, and marketable 

potato yields were lowest among treated plots. Adding metribuzin to 

pendimethalin increased Russian thistle control to 95%, and increased 

marketable tuber yields by 54% over pendimethalin alone. Previous research 

has indicated that pendimethalin may have a beneficial effect on potato yields 

beyond that of weed control, possibly by inducing deeper rooting (Nelson 

and Giles, 1989). 

5

V.D. Mircov et al. 

Table 1. Prostrate pigweed, kochia, and Russian thistle control, and potato 

yields, averaged over three years (2002–2004). 

Treatments Timing Rate 

Weed control a Marketable b 

AMABL KCHSC SASKR potato yield 

l/ha –1 % t/ha –1 

Trifluralin+metolachlor PPI 0.75+1.5 100 89 95 40.6 

Trifluralin+EPTC PPI 0.75+3.0 100 88 95 40.9 

Trifluralin+EPTC+metribuzin PPI 0.75+3.0+0.25 100 100 100 42.5 

Fluorochloridone PRE 0.25 100 100 90 42.0 

Fluorochloridone PRE 0.50 100 100 99 38.5 

Pendimethalin PRE 1.0 100 99 69 28.9 

Pendimethalin+EPTC PRE 1.0+3.0 100 100 70 33.8 

Pendimethalin+metribuzin PRE 1.0+0.25 100 100 95 44.5 

Metolachlor+ metribuzin PRE 2.0+0.25 100 100 96 43.3 

Metribuzin PRE 0.5 100 100 100 45.4 

Weed – free control 100 100 100 43.2 

Unweeded control 0 0 0 28.7 

Lsd (0.05) 1 5 6 30 

a AMABL–prostrate pigweed; KCHSC–kochia; SASKR–Russian thistle; 

b Tubers 28/55 in diameter; 

Combining pendimethalin and metribuzin did not significantly change 

marketable tuber yield as compared with metribuzin alone or the weed–free 

control in these experiments. Though fluorochloridone at 0.5 l/ha controlled 

all weeds in this study, marketable tuber yields from this treatment were 

lower than the weed–free control. The early injury appeared to have a 

deleterious effect on the crop, at least at the higher rate. 

Controlling prostrate pigweed, kochia, and Russian thistle at the 

beginning of the season increased marketable potato yields more than 100% 

compared with the unweeded control. Yields were greatest where weeds were 

controlled with no injury to the crop. All herbicide treatments in this research 

with the best broadleaf weed control and no crop injury contained metribuzin. 

Conclusions 

Study results emphasize the need for good weed control for optimum 

potato yields. Metribuzin applied alone or in combination with metolachlor, 

pendimethalin, or trifluralin plus EPTC gave excellent broadleaf weed 

control and the highest marketable potato yields. 

6

Results of weed control in field potatoes 

References 

NELSON, D. C. AND J. F. GILES. (1989): Weed management in two potato (Solanum 

tuberosum) cultivars using tillage and pendimethalin. Weed Sci. 37:228–232. 

NELSON, D. C. AND M. C. THORESON. (1981): Competition between potatoes (Solanum 

tuberosum) and weeds. Weed Sci. 29:672–677. 

THAKRAL, K. K., M. L. PANDITA, S. C. KHURANA, AND G. KALLOO (1989): Effect 

of time of weed removal on growth and yield of potato. Weed Res. 29:33–38. 

VANGESSEL, M. J. AND K. A. RENNER (1990): Redroot pigweed (Amaranthus 

retroflexus) and barnyardgrass (Echinochloa crus–galli) interference in potatoes 

(Solanum tuberosum). Weed Sci. 38:338–343. 

WALL, D. A. AND G. H. FRIESEN. (1990a): Effect of duration of green foxtail (Setaria 

viridis) competition on potato (Solanum tuberosum) yield. Weed Technol. 4:539–542. 

ROSALES – ROBLES, E., J. M. CHANDLER, S. A., SENSEMAN, AND E. P. PROSTKO 

(1999): Influence of growth stage and herbicide on post – emergence johnsongrass 

(Sorghum halepense L.) control. Weed Tech. 13: 525 – 529. 

BAZIRAMAKENGA, R., AND G. D. LEROUX (1998): Economic and interference 

threshold densities and quackgrass (Elytrigia repens L.) in potato (Solanum 

tuberosum L.). Weed Sci., 46: 176–180. 

7

Herbologia Vol.7, No. 1, 2006. 

SOIL MANAGEMENT AND TILLAGE POSSIBILITIES IN WEED 

CONTROL 

Anikó Farkas 

Szada, H-2111, Szabadság u. 58. 

E-mail: letics@citromail.hu 

Abstract 

On the basis of the research done on interactions between tillage, soil 

condition and weediness, conclusions are listed in three main point and 18 

sub-points. 

a) Importance of favourable soil condition 

1. The weather data of the region affirm the growing frequency of dry 

years and the tendency of weather extremes. This shows the necessity 

of tillage systems that increase the water absorbing and water retaining 

capacity of the soil. Tillage methods that improve and maintain soil 

condition may gain prominence. The cover of the soil between crops 

and the introduction of crops that have a beneficial effect on yield may 

become a necessity. 

2. The effect of previous years can be shown by exact soil condition 

examinations, and on this basis the methods of improvement can be 

planned and implemented. The danger of plough-sole and disk-sole is 

present on the soil. The damage can be alleviated by cultural and 

biological methods. 

3. The disk-sole formed after the stubble-clearing of mustard confirmed 

the importance of consideration of the soil humidity. Tillage was 

enough to break compaction close to the surface (with the exception of 

direct drill), which means that smaller damages can be alleviated. 

4. The sowing and germination of oil radish may be influenced by the soil 

condition changed by the tillage method under the main crop. The soil 

loosening effect of the oil radish did not appear in case of direct 

drilling, which probably shows the sensitivity of the crop to the soil 

condition. 

b) Evaluation of soil condition and nutrition level 

1. The role of good soil condition and nutrition level in the reduction of 

drought damage was proven again in wheat, maize, and spring barley. 

2. The 35-45 cm deep loosened soil condition had the best influence on 

yield in the biologically favourable crop rotation system, which was 

achieved by loosening combined with disking. In dry vegetation period

Aniko Farkas 

the beneficial effect of tillage methods saving the soil structure 

(cultivator) is also obvious. 

3. In winter wheat and maize the yield limiting effect of direct drill is 

explained by weediness and the hindrance of water movement in the 

soil of the experimental field, susceptible to sedimentation. 

4. The yield of maize sown after oil radish was influenced by the 

loosening of soil and the nutrition level. While in winter wheat water 

retaining played a significant role in the whole growing season, in the 

year of maize there were droughts only in the spring. This shows that 

the yield of maize was influenced more by the water retaining effect of 

the soil condition influenced by tillage methods than the precipitation in 

the growing season. 

5. The undisturbed soil condition characteristic of direct drill did not 

hinder the utilisation of fertilizer in maize, in a year with average 

precipitation. It can be stated that in case of good nutrition level the 

yield-reducing effect of compacted or sedimented soil can be alleviated. 

c)Evaluation of crop rotation order according to weediness 

1. The introduction of mustard in the crop rotation is advantageous 

because of its weed-limiting, soil-covering and soil-improving effect. 

With mulching at an optimal date the weed-promoting effect of the 

catch-crop and the unnecessary water loss can be avoided. 

2. On the stubble of mustard and winter wheat weeds characteristic of the 

area appeared. The higher weed coverage in summer – and thus the 

better timing of plant protection and the reduction of the seed-bank – 

was aided by the favourable loosening and humidity of the soil. 

3. The soil loosening effect of oil radish was proven by penetration values. 

It can be used as a protecting crop in dry years if soil humidity loss is 

curbed during the sowing. The crop improved the cultivability of the 

soil and was proven to be a good green crop because of its good 

coverage, rooting and its weed limiting effect. 

4. The good weed-limiting effect of the soil is proven, in accordance with 

the literature, which was further increased be the greater water loss of 

the soil. This makes the re-evaluaton of the role of ploughing necessary. 

5. Tillage methods can be ranked according to their weed-promoting or 

weed-limiting effect. Among the same conditions direct drill has a 

weed-promoting, while regular soil-turning has a weed-limiting effect. 

The weed-promoting or limiting effect of tillage methods without soil 

turning (loosening, cultivator treatment, disking) is different in each 

crop and at each nutrition level. Loosening is good to curb the life 

activity of perennial crops. 

10

Soil management and tillage possibilities in weed control 

6. The high proportion of Echinochloa crus-galli in the total coverage and 

its prominent rank in the order proves its adaptation to the different soil 

and nutrition conditions. 

7. The disking under spring barley modified the morpho-biological 

spectrum. The coverage of the perennial Elymus repens increased, 

utilizing well the higher level of nutrients. 

8. According to the coverage of Ambrosia artemisiifolia ploughing was 

put at first place in the order of tillage methods. The high number of 

seeds appearing after the turning of the soil showed greater infection. 

9. The competitiveness of Ambrosia artemisiifolia shows a tendency. On 

soils with low nutrient supply it is more competitive than other weeds 

and crops. It reacted with higher coverage to the low nutrition level. In 

case of good nutrition level the weed-limiting effect of cultivated crops 

is higher, but the development of competing, less dangerous weeds is 

also better, against which plant protection is easier. 

Introduction 

The analysis of traditional tillage systems has a significant place 

among crop production research topics. In the past 20 years several essays 

were published on the effect of low tillage and no-till systems on cultivation 

factors, mainly overboard. The actuality of the analyses is justified by the 

different cost demand, the necessity and difficulty of creating harmony 

between the inputs and the more exact knowledge of the plant protection 

effects of certain systems. In different soil tillage systems tillage influences 

physical condition and weediness just like crop rotation order and other 

elements of agrotechnique. 

One of the unfavourable effects of tillage is soil compaction that presents 

production risk on 1.4 million hectares in Hungary. Tillage originated 

compaction can be meliorated by mechanical (loosening) and biological 

(plants having favourable effect on soil condition) methods. 

Weediness is related to soil utilization, tillage and the professionality 

of plant protection. The yield loss due to weeds can reach or exceed the 30% 

of the total loss. Due to the damage of weeds, the protection against them is 

inevitable. 

As a consequence of structural and financing problems the cultural 

condition of the soils deteriorated and weeds proliferated, many species are 

hard to kill. The problem is not new. As a result of the herbicide utilization of 

the previous years resistant biotypes gained prevalence and the tolerance 

against chemicals increased. 

The realization that herbicides have a negative effect on the 

environment and food safety influenced the weed control practice positively. 

11

Aniko Farkas 

One sign is the ambition to keep the weed coverage under the harmful limit. 

The result is the reducing of herbicide use to reasonable levels, that is also 

eligible according to the EU and international regulations. The application of 

weed control measures can be aided by the requirements of agriculturalenvironmental 

programmes and subsidies, the weed controlling effect of soil 

tillage, the expansion of reduced crop rotation with catch-crops with a 

beneficial effect on soil condition and weed control. 

The reasons and factors mentioned above make the comparing 

analysis of different soil tillage systems useful. 

According to this, the objectives of this research were 

1. analysis of weediness changing as a result of different cultivation 

methods, with emphasis to the various nutrition levels; 

2. analysis of the effect of soil condition forming and changing as a 

result of various tillage methods on the weediness, with new 

analytical methods; 

3. determining whether the low tillage can be complied with the 

appropriate control of weeds; 

4. reaction of some important weed species to the treatments; 

5. conclusion on the basis of the results and formulating the 

recommendations that can be used in practice. 

Material and method 

On the Experimental Station of the predecessor of title of the Szent 

István University (GATE) several different cultivation treatments were 

compared in a soil tillage trial on the basis of their effects on soil condition, 

yield and weediness. The significance of the examinations is increased by the 

judgement of the effects of tillage and fertilization and the introduction of 

catch-crops into the crop order. 

The experimental field is in the Gödöllı hills. The soil (liable to 

sedimentation, sandy loam) and the precipitation conditions make the yield 

safety fluctuant, and the number of crops that can be cultivated economically 

is low. The year 2000 and 2002 were drier than the average, the years 1999 

and 2001, on the other hand, had more rain. 

In the two factorial, strip small plot trial with four replications (a) 

signifies the soil tillage methods, (b) the fertilization treatments. Plot sized 

are 5x20 m= 100m 2 . The order of crops is: white mustard in 1999, followed 

by winter wheat, after the harvest of wheat oil radish, maize in 2001, spring 

barley in 2002. The date of weed surveys is shown in Table 1. Table 2. 

includes the data of on the cropping practices in the trial. 

12


Table 1.: Dates of weed surveys (Gödöllı, D trial) 

Year Crop 

Date of weed survey 

1 2 3 

1999 white mustard 05. 27. 

08. 22. 

(stubble) 

2000 winter wheat 04. 20. 05. 16. 06. 16. 

2000 oil radish 08. 24. 

2001 corn 06. 06 08. 20 09. 27 

2002 spring barley 04. 16. 05. 27. 07. 08 

Treatments employed in the trial and their levels: 

Soil tillage: 

a 1 : Ploughing (22-25cm): traditional system with several turns 

a 2 : Loosening (35-40cm) + disking (16-20cm): soil condition 

improving system 

a 3 : Tillage system based on heavy cultivator (16-20cm), low-till and 

low cost system 

a 4 : Direct drill: no-till, soil condition maintaining system 

Fertilization in the autumn: 

b 1 : 80 kg N + 60 kg P 2 O 5 + 60 kg K 2 O /ha active agent (low dose 

according to the soil supply), 

b 2 : 160 kg N + 120 kg P 2 O 5 + 120 kg K 2 O /ha active agent 

(optimal dose according to the soil supply). 

Table 2.: Cropping practices in the trial (Gödöllı 1998-2002) 

Term 1999 2000 2000 2001 2002 

Crop 

Objective 

Species 

Sowing time 

Harvest time 

Vegetation period, days 

Preceding crop 

White mustard 

Mulch 

mixed 

4. 12 

6. 29. (stem.) 

79 

winter wheat 

Winter wheat 

Grain 

Mv MAGVAS 

’99. 10. 28. 

7. 13. 

258 

white mustard 

Oil radish 

Mulch 

mixed 

8. 4. 

frozen (Oct) mulch 

89 

winter wheat 

Maize 

Grain 

PR36R10 

2001.5. 4. 

2000. 10. 15. 

143 

oil radish maize 

Tillage method 

Date of tillage 

Seedbed preparation 

Top-dressing 

Plant protection (weed control) 

Pests, diseases 

Number of plants/m 2 a 1 b 1 

a 1 b 2 

a 2 b 1 

a 2 b 2 

a 3 b 1 

Ploughing 

1998. 10. 28. 

4. 10. 

- 

- 

165 

162 

160 

156 

158 

4 treatments 

1999. 9. 28-29. 

10. 8. 

2000. 3. 23. 

2000. 4. 24. Segal 65 

WG 

- 

- 

460 

566 

504 

575 

480 

Disking 

2000. 7. 17. 

8. 4. 

- 

- 

- 

102 

111 

110 

120 

110 

3 treatments 

2000 10.31. 

2000.5.14 

2001. 5. 18. 

Post: Titus plus 

- 

- 

64.300/ha 

64.600 

64.800 

64.880 

65.200 

Spring barley 

Grain 

Amulet 

2002.03. 22. 

2002. 07. 03 

104 

2 treatments 

2002. 03. 16-19. 

2002. 03. 21 

2002.04. 12. 

- 

- 

180 

220 

210 

240 

200 

13

Aniko Farkas 

a 3 b 2 

162 

570 

116 

65.300 

210 

a 4 b 1 

a 4 b 2 

160 

162 

310 

390 

102 

112 

63.600 

63.900 

150 

190 

Plot m 2 5x20 = 100 100 100 100 100 100 

Appearance of shoots 

1999 11. 20. 2000.08.10-15. 2001.05.12. 

Other: 

Fertilization residue nutrients fertilization 

1999. 04. 16. 

Without 

fertilization 

according 

treatment 

09. 18. 

to 

according 

treatments 

2000. 10.31. 

Methods of examination 

Method of weed seed content analysis: On the stubble of the white 

mustard the upper 10 cm layer of the soil was analysed on the basis of ten 

200 cm 3 samples. Weed seeds were isolated with ZnCl 2 sedimentation 

method. The size of the seed-bank determining the potential infection was 

determined for 1 m 2 . 

Method of weed survey: Weed covering examinations were carried 

out with the 1 square meter (modified Balázs-Ujvárosi-type) quadrat method. 

In white mustard and its stubble coverage percentage was measured at ten 

places each time. Measurements were taken three times in winter wheat, 

maize and spring barley, and once in oil radish. Evaluation was carried out by 

variance analysis. 

Method of yield evaluation: The yield data from the plots was 

calculated for one hectare. Data was evaluated by variance analysis. 

Method of soil condition analysis: To measure soil resistance the 

Daróczi-Lelkes-type PENETRONIK penetrometer was used. The resistance 

of the upper 40 cm layer of the soil was measured every 5 cm, together with 

humidity. 

Evaluation of the reaction of Ambrosia artemisiifolia L.: The 

different tillage methods were evaluated and placed in order on the basis of 

their Ambrosia artemisiifolia controlling effect. 

Demonstration of the direct effect of soil resistance on weediness: 

The direct effect on soil resistance on weediness was demonstrated by rank 

correlation. Rank correlation was carried out according to the steps given by 

SVÁB (1981). 

Results 

1. Result of the seed content analysis 

From the samples taken from the stubble of white mustard it was seen 

that the area is infected mainly by annual weeds. The composition of the 

seed-bank consisted mainly of T 4 -type species. Less seeds belonged to other 

annual and perennial species. Late summer annuals contribute to a diverse 

seed-bank in the soil (Table 3.). On the basis of the 20 species the soil is not 

to 

Residue nutrients 

14


considered rich in weeds. This tendency is apparent also on the field. The 

tillage systems, the simplified crop rotation and the employed agrotechnology 

(chemical plant protection) all contribute to the decrease of weed diversity. 

As for the life form of seed-bank species, the predominance of warm 

demanding species is obvious. Weed seed content per 1 m 2 was 38250, 

infection is considered low. 

Table 3.: Seed-bank of the soil, Gödöllı, 1999 

Life form 

Number of Number 

species of seeds 

% 

G 1 1 3 0,39 

G 3 1 1 0,13 

H 3 2 4 0,52 

H 4 1 1 0,13 

Perennials 5 9 1,18 

T 1 2 28 3,66 

T 3 1 1 0,13 

T 4 12 727 95,04 

Annuals 15 756 98,82 

Total 20 765 100 

Results of the weed surveys 

In white mustard total coverage was average in May (9.31%). The 

development of the species of the first aspect (7,14 %) were aided by the 

precipitation. T 4 life form species that were characteristic of the area had 

many germinated plants, but their total coverage is low (1.66 %). Annuals 

contributed to the 98% of the total weed coverage. 

On the stubble of mustard weed coverage was much higher (71,02 

%)compared to the spring results. Germination after harvest was significant 

with its 8.1%, and was the fourth in the order. This means that the time of 

mulching of the protective crop and the tillage for the following crop has to 

be chosen more carefully in case of wet weather than in an average 

vegetation period. The development of T 4 species forming the third aspect 

(58.71 %) was aided by high precipitation and high temperature. 

There were three monocotyledonous weeds present (Digitaria sanguinalis, 

Echinochloa crus-galli, Elymus repens). Their total coverage is 9.23 %, from 

which perennials presented 1.32 %. The proportion of monocotylednonous 

plants in the total coverage increased from the initial 2.15% to 13%, with 

Digitaria sanguinalis and Echinochloa crus-galli playing a significant role. 

The number of species was 19 and 28 at the two dates. 

15

Aniko Farkas 

In April in winter wheat the weeds of the T 1 group dominated in 

accordance with the date of the survey. The formerly typical cereal weeds 

had a low cover percentage. Due to the favourable weather conditions, the 

lack of many competitors, and the slower development of the wheat, many 

germinated T 4 plants were found. From among monocotyledonous weeds, 

Echinochloa crus-galli was significant. The scope of the presence of T 4 

weeds is in accordance with the other experiences in the country, and warns 

about the tendency and the necessity of creating a proper crop rotation. In 

case plant protection was not effective against these species, in next year’s 

intertilled crop the weed problem may increase. 

Since total coverage consisted in large part of species sensitive to the 

applied active agents, the sensitive and early annuals thinned or disappeared 

by May. 

By June perennials – especially Elymus repens – had the highest 

coverage, but differently at the two nutrient levels. Their role in total 

coverage and in determining the differences between tillage methods is 

similar to the role of annuals in April. 

Considering the June data it can be said that if nutrition is 

unfavourable, tillage methods without soil-turning may prove to be weedpromoting. 

On the other hand, if nutrition is appropriate, the disadvantage of 

these tillage methods disappears. The effect of direct drill is antinomic, 

according to the literature, because both its weed controlling and weed 

promoting effect was seen. 

It is favourable that the coverage of perennials is not too high and 

their upsurgence in maize is less expected. Within total coverage the 

proportion of monocotyledonous plants was rising. 

Because of the dry vegetation period wheat did not tiller properly, and 

therefore its weed-limiting effect was less. It is probable that this was the 

reason why the weed-controlling effect of ploughing could not manifest. 

On the basis of the survey taken in oil radish the predominance of E. 

crus-galli was obvious compared to annuals and the total coverage, at 

optimal nutrition level. In the average of the four treatments annual 

monocotyledonous plants contributed to 74.99% of the total coverage. E. 

crus-galli has a special significance, because maize was following oil radish. 

In maize Echinochloa crus-galli had a high coverage at the time of 

the first survey; compared to the others, with the exception of cultivator 

treatment on low nutrition level where the coverage of Elymus repens was 

close to 4%. Because of the late survey, in the case of the other species more 

T 4 weeds appeared. 

At the time of the second survey the coverage was tenfold. E. crusgalli 

was again the first. A Digitaria sanguinalis, which was missing in June, 

climbed to the second place. The coverage of Ambrosia artemisiifolia also 

16


increased, just like the cover percentage of E. repens and Convolvulus 

arvensis. 

By September the weed coverage decreased. Many weeds finished 

their life activity and the shadowing of the maize was also acceptable. E. 

crus-galli still had a high coverage, but shared its place with the formerly 

insignificant Solanum nigrum and A. artemisiifolia. 

The spring barley was lacking weeds, which was caused probably by 

the low precipitation and the coverage of barley. At the time of the late 

survey mainly perennials (E. repens) and T 1 species were present, with S. 

media as the most characteristic. The adaptability of A. artemisiifolia is 

obvious, since young plants were seen even at this date. 

By the time of the second survey the field still had low weed 

coverage, with the exception of direct drill treatment with higher nutrition 

level. T 4 life forms gained prevalence, with E. crus-galli having the highest 

coverage. A. artemisiifolia had an almost similar coverage in the cultivator 

treatment at optimal nutrition level. 

In July after the harvest the coverage was obviously low, but E. crusgalli 

still had the highest coverage. 

It can be stated that in the weed population that is poor in species T 4 

weeds had the highest significance. This is probably the result of the 

cultvation practice of the previous years. 

As a result of the weed condition after white mustard sown as an 

adjusting crop, the effect of the treatments can be evaluated reliably in winter 

wheat. In April and June the interaction of the two factors was apparent, so 

nutrition influenced the weed limiting or promoting effect of the cultivation 

treatments. 

At the first date the disking + loosening combination limited the 

development of annuals better than cultivator treatment at low nutrition level. 

Since total coverage was determined by annuals this was also true for total 

coverage. In case of higher nutrition level weed coverage was higher in 

treatments without soil turn, but the difference is not significant, which 

means nutrition had a balancing effect. 

Weed condition in May was influenced by herbicide treatment to such 

an extent that the interaction of treatments and the weed-promoting effect 

cannot be demonstrated. 

According to the results in June the wed limiting effect of ploughing 

is just tendential at minimal nutrition level. Nutrition modifies this and in 

case of optimal fertilizer level the other treatments curb weeds more than 

direct drill. 

Tillage preceding the sowing of oil radish and the development of oil 

radish balanced the weed condition. The weed limiting effect of ploughing 

17

Aniko Farkas 

was obvious at both nutrition levels. The tillage accompanying the sowing of 

oil radish had an effect on weediness also later. 

In maize the interaction of the tillage and fertilizer treatments could 

not be demonstrated. It is obvious that the weed limiting effect of ploughing 

could be demonstrated in the average of the three dates. The other treatments 

had a different effect depending on the level of nutrition but statistically this 

effect is not authentic. 

In barley the weed limiting effect of ploughing and the weed 

promoting effect of direct drill is showing a tendency. 

The most significant weed of our days, Ambrosia artemisiifolia L was 

evaluated separately. Its coverage was considerable at both nutrition levels. 

In winter wheat and maize it had tendentially higher coverage on soils with 

proper nutrition supply. On the other hand, depending on the year, it utilized 

low level nutrients better than competitive weeds and the crop. This shows 

that A. artemisiifolia can be limited by appropriate fertilization and the 

cultivation of weed limiting crops. This is in accordance with the demand for 

harmony between resources. 

Between the different tillage treatments the favourable or 

unfavourable effect on the weed cannot be determined. In the order of 

treatments the ploughed soil was the most favourable for A. artemisiifolia. 

This means that on the weed-infected field the weed-bank of the soil also aids 

the proliferation of the weed through annual ploughing. 

2. Yield results 

Examinations were carried out in biologically favourable crop rotation 

system. The crop order of the trial is not typical because of the introduction 

of oil radish. Therefore the results can be used also from the viewpoint of 

sustainable crop production and integrated technologies. 

The yield was the best in case of soil loosened favourably 35-45 cm 

deep, independently from the weather of the year. Somewhat lower yield was 

harvested from soil tilled with cultivator, and ploughing was the third in 

order. In every case the yield was lowest in direct drill treatment. On similar 

soils, where direct drill can be favourable because of its soil protecting 

function, the lower yield and its effect of weediness call for careful 

consideration. In case of professional and continuous chemical protection 

weediness can be reduced, and this may have environmental consequences. 

The weed limiting effect of loosening is not satisfactory, with the exception 

of perennial weeds, but its favourable effect on the soil provides an economic 

advantage of ploughing, that has otherwise a better weed limiting effect. 

In winter wheat and spring barley the interaction of the two factors is 

not apparent, but fertilization had yield increasing effect in all treatments, 

18


most strongly in loosening + disking treatment. The drough damage lessening 

effect of fertilization was demonstrated in accordance with literature. 

The undisturbed soil condition characteristic of direct drill did not 

limit the favourable utilization of fertilizers in case of maize, in a year with 

average precipitation. It can be stated that the yield limiting effect of 

compacted or sedimented soil condition can be reduced. 

3. Effect of introducing a catch crop between the main crops 

The favourable biological effect of crop rotation was increased both 

by white mustard and oil radish. Favourable effect was shown in the better 

cultivability of the soil. On given soil that is susceptible to sedimentation the 

duration of soil loosening is short and the effect can be lengthened by crops 

with a loosening effect. 

4. Change of soil condition 

A compacted layer forms under the layer of annual ploughing, which 

can extend also towards the upper layers. The loosening effect of oil radish 

improved the soil condition, and this effect was shown also in the deeper 

layers. Under the depth of the basic tillage for the next crop (maize) the 

penetration values were higher but the thickness of the plough-sole 

decreased. 

The flaws of the previous years were demonstrated mainly in the 

shallow tillage treatments. The 35-45 cm deep loosening of the soil alleviated 

this problem, and no soil resistance above 3 MPa (critical value) was 

measured. The loosening effect of oil radish was reduced somewhat by the 

disking following loosening. 

In soil tilled with cultivator a more compacted layer formed under the 

layer in question. The loosening effect of oil radish could be shown down to 

25 cm depth. 

In direct drill plough-sole shows the previous soil-turning tillages. In 

the second year the soil is compacted under the sowing, in the upper 10 cm of 

the soil. The loosening effect of oil radish was demonstrated only in the 

upper 15 cm layer but this effect disappeared in the next year. It is important 

that weeds endure compacted soil condition while in case of cultivated crops 

the yield is depressed because of the competition and the limiting effect on 

rooting. 

5. Results of rank correlation 

The basic hypothesis of my work was that the soil condition 

influences the development of the weeds and plant organisms directly. It was 

assumed that in a certain depth soil condition affects weediness. If treatments 

are put in order on the basis of MPa values measured in ascertain depth, 

19

Aniko Farkas 

weediness is related to this order. According to the calculated values of the 

rank correlation the connection of the two orders of the treatments can be 

demonstrated only in a few cases. This can be due to the fact that treatments 

change the looseness of the soil in different depths and extents and in a crop 

the different plant populations are presented in different proportions, thus 

affecting the order and rank correlation also. On this basis the analysis of 

pure stands with different tillage methods is recommended. 

Examining the rank correlation in function with the depth certain laws 

can be observed. To determine mathemaical relationship a dot diagram was 

created, fitting the sixth degree polinom of EXCEL as a trend line. Different 

R 2 values were calculated for the different dates and weed groups, but those 

show the strong fit of the polinom. The example is shown on the weed and 

soil conditions of winter wheat in Table 4. 

Table 4.: Rank correlation depending on sample depth, Gödöllı 

R 2 

Winter wheat 2000 April May June 

* 

rankcor 1 0,93 0,36 0,78 

** Annual 

rankcor 2 0,82 0,91 0,98 

rankcor 1 0,89 0,91 0,91 

Perennial 

rankcor 2 

0,83 0,91 0,63 

rankcor 1 0,75 0,86 0,97 

All 

rankcor 2 

0,88 0,83 0,63 

Key:* at minimal nutrition level, ** at optimal nutrition level 

It can be seen in Table 4. that the value calculated on the basis of the 

coverage of annual weeds in winter wheat in May is low. This is in 

accordance with the fact that because of the chemical plant protection 

annuals are almost gone from the field. Among “unnatural” conditions this 

law does not manifest. In June the value of perennials and total coverage is 

average, this is probably due to the fact that the role perennials played in total 

coverage is different in each treatment. 

The results justify the necessity of other, similar examinations, despite 

the difficulties. 

6. New scientific results 

On the basis of the analyses of tillage, soil condition and weediness the 

following new scietific results were determined. 

1. On Gödöllı brown soil the relationship between the favourable 

loosening of the root zone and the yield was obvious in dry year. The soil 

condition created by ploughing ensures average yield. 

2. On soil that is prone to sedimentation the yield reducing effect of 

direct drill in winter wheat, maize and spring barley was caused by bad soil 

condition and the higher coverage of less susceptible weeds. 

20


3. Tillage methods were put into order according to their weed-limiting 

effect. The weed promoting effect of direct drill and the weed limiting effect 

of regular soil-turning was proved together with the modifying effect of crop 

rotation order and nutrition level, especially in the case of tillage without 

soil-turning (loosening, cultivator treatment, disking). 

4. On the basis of the decreasing coverage of Ambrosia artemisiifolia L. 

ploughing was put to the first rank as the most favourable tillage method for 

the development of the species. The great competitiveness of A. artemisiifolia 

had a tendency, especially among low nutrition conditions. 

5. Analyses carried out during the 4 years of the experiment made rank 

correlation possible. It was determined that the method can be further 

improved by calculations per species. Since the competition of species is seen 

among cultivation conditions, pure stands and more tillage methods can be 

taken into account. 

6. The dependence of rank correlation on tillage depth was proven by 

fitting a polinom. More analyses are necessary to justify or reject the 

accuracy of the method. 

Summary 

The hypothesis was that soil condition affects weeds as plants 

directly. The competition for nutrients also influences the predominance of 

plant potential. As a result appropriate soil management can avert not only 

the further deterioration of our soils but weeds can also be forced back. The 

significance of the research is increased by the examination of protecting 

intercrops. The introduction of these plants (originally used as green manure) 

enables the biological improvement of soils and weed control. Special 

attention was given to the adaptation ability of Ambrosia artemisiifolia. New 

methods were employed together with weed surveys and soil resistance 

measurements. On the basis of rank correlation other relationships could be 

discerned. 

The growing probability of the more frequent drought years and the 

tendency of extreme weather indicate the necessity of tillage systems that 

increase the water absorbing capacity of the soil and that retain the water. 

Tillage systems that improve and maintain soil condition should get 

into the foreground. The coverage of soil between two main crops also 

becomes necessary, and the introduction of crops having a beneficial effect 

on soil and yield into the crop rotation also. 

The effect of the tillage used in the previous years can be 

demonstrated and thus the methods for improvement can be planned and 

carried out. The damage can be alleviated by tillage and biological methods. 

The disk-sole appearing because of the stubble-clearing of white mustard 

21

Aniko Farkas 

showed the importance of adaptation to the water content of the soil. To 

eliminate the compaction of soil near the surface all tillage methods (with the 

exception of direct drilling) were sufficient, thus presenting several 

possibilities to improve lesser damages. The loosening effect of the roots of 

oil radish was missing in case of direct drilling, which shows that the plant is 

susceptible of soil condition. 

The importance of good soil condition and nutrition in the reduction 

of drought losses was demonstrated again. Yield was affected most 

favourable by 35-45 cm deep loosening. In dry vegetation period besides 

loosening methods that spared the soil structure (cultivator) also had a 

favourable effect. On the soil of the experimental area the yield reducing 

effect of direct drilling in wheat and maize can be explained by weeds and 

the blocking of water transport. 

The yield of maize following oil radish went according to the 

loosening of soil and its nutrient supply. The yield of maize was influenced 

more by the water retaining capacity of the soil than by the precipitation in 

the vegetation period. The undisturbed soil condition of direct drilling did not 

hinder the utilization of fertilization in case of maize in a year with average 

precipitation. It can be stated that in case of good nutrition supply the yield 

reducing effect of compacted or sedimented soil can be diminished. 

The mustard in the crop rotation had a favourable effect. By mulching 

at the appropriate time we can avoid the weed-promoting effect of the 

intercrop and the unnecessary water loss. The greater weed coverage in the 

summer periods was promoted by the favourable loose condition and the 

water content of the soil, and this way plant protection measures could be 

timed and the weed seed base decreased. 

The soil loosening effect of oil radish was proved by soil resistance 

values. It can be employed as protecting crop in dry years if the reduction of 

soil water loss is emphasized during the sowing. Oil radish improved the 

cultivability and ensured a good green crop effect. 

The direct drilling has a weed promoting effect, while ploughing 

reduces the weeds. Tillage methods that do not turn the soil (loosening, 

cultivator, disk tillage) have different weed promoting or prohibiting effects 

in case of the various plants and nutrition levels. 

The development of the Ambrosia artemisiifolia is the best among 

conditions created by ploughing (the dormant seeds get into the germination 

zone). The great competition ability of Ambrosia artemisiifolia has a 

tendency for having a greater coverage in case of lower nutrition level. In 

case of better nutrition the weed-limiting effect of cultivated crops is higher, 

and plant protection is easier to apply. 

22


The accuracy of the rank correlation method still needs further 

analysis. In the future the evaluation of “pure” weed stands and the analysis 

of data separated according to species and life forms are expected. 

Acknowledgements. The research programs supported by OTKA 32851 and OTKA 34274 

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DORNER, Z., NÉMETH, I., FARKAS, A. The effect of extensive farming on the weed 

composition of cereals between 2000 and 2003 in Hungary. 22. Deutsche 

Arbeitsbesprechung über Fragen der Unkrautbiologie und –bekämpfung Stuttgart- 

Hohenheim, Euroforum 2. - 4. März, in Zeitschrift für Pflanzenkrankheiten und 

Pflanzenschutz, Sonderheft XIX. p. 113-117. 

FARKAS, A. 2004. The effect of cultivation methods on soil compaction and weediness in 

oil seed rape grown as a cover crop in Gödöllı. VII. Kongress on weeds. Serbia, 

Palic, 7-11. Jun. 2004. Acta herbologica, Beograd, 13. 2. p. 379-384. 

FARKAS I-NÉ, VINCZE M., KASSAI M. K. 2000. Mővelés, talajállapot és gyomosodás 

összefüggései (Effect of Soil Tillage on Soil Condition and Weed Infestation). 

MTA AMB. 24. Kut. és Fejl. Tanácskozás, Gödöllı, jan.18-19. Kiadvány (szerk. 

Tóth L., Benkóné Pongó D.), 2. köt. pp. 15-19. 

FARKAS I-NÉ, VINCZE M., PERCZE A., KASSAI M. K. 2001. A gyomszabályozás 

agrotech-nikai lehetıségeinek vizsgálata gödöllıi termıhelyen (Examination of 

Agricultural Possibilities of Weed Control at Gödöllı Site), MTA AMB. 25. Kut. és 

Fejl. Tanácskozás, Gödöllı, jan.23-24. Kiadvány (szerk. Tóth L., Benkóné Pongó 

D.), 2. köt. pp. 106-110. 

FARKAS A., PERCZE A., VINCZE M. 2001. A SEGAL 65WG hatása különbözı 

talajhasználati rendszerekben. 47. Növényvédelmi Tudományos Napok, Budapest, 

MTA, 2001. febr. 27-28., Kiadvány (szerk. Kuroli G., Balázs K., Szemessy Á.) p. 

125. 

FARKAS A. 2001. Környezetbarát növényvédelemért-agrotechnikai gyomirtással. VII. 

Ifjúsági Tudományos Fórum. Keszthely, 2001. márc. 29. CD-kiadvány 

FARKASNÉ SZERLETICS A., Ujj A. 2001. Talajhasználati tartamkísérletek a környezetgazdálkodás 

szolgálatában. MTA MTB II. Növénytermesztési Tudományos Nap 

29

Aniko Farkas 

„Integrációs feladatok a hazai növénytermesztésben” Proceedings (szerk. Pepó P., 

Jolánkai M.), pp. 180-184. 

FARKASNÉ SZ. A., GYURICZA Cs. 2001. Különbözı mővelési eljárások 

gyomviszonyokra gyakorolt hatásának összehasonlító értékelése gödöllıi 

termıhelyen. XLIII. Georgikon Napok, Keszthely, 2001. szept.20-21. Kiadvány 2. 

kötet, pp. 845-849. 

FARKASNÉ SZERLETICS A. 2002. A parlagfő (Ambrosia elatior) jelenléte és borítási %- 

ának változása különbözı mővelési eljárások hatására. 48. Növényvédelmi 

Tudományos Napok, Budapest, MTA, 2002. márc. 6-7., Kiadvány (szerk. Kuroli 

G., Balázs K., Szemessy Á.) p. 110. 

FARKASNÉ SZERLETICS A. 2002. Gyomborítás változása különbözı talajmővelési 

eljárások hatására gödöllıi termıhelyen (Effect of Different Soil Tillage on the 

Weed Flora on Sandy Loam Soil). Innováció, a tudomány és a gyakorlat egysége az 

ezredforduló agráriumában. SZIE–DE ATC, Debrecen, 2002. április 11-12. 

Kiadvány „Növénytermesztés” (szerk. Jávor A., Sárvári M.), pp.312-317. 

FARKASNÉ SZERLETICS A., DORNERNÉ FEJİS Z., NÉMETH I. 2002. A parlagfő 

borításának alakulása eltérı tápanyagmennyiségek hatására gödöllıi termıhelyen. 

HWRS Konferencia, 2002. nov. 14. 

DORNERNÉ FEJİS Z., BLASKÓ D., FARKASNÉ SZERLETICS A., NÉMETH I. 2002. 

Vetésforgókísérlet biotermesztésben. HWRS Konferencia 2002. nov. 14. 

FARKASNÉ SZERLETICS A. 2003. A parlagfő (Ambrosia artemisiifolia L.) borításának 

változása eltérı tápanyagmennyiségek és talajmővelés hatására. XIII. Keszthelyi 

Növényvédelmi Fórum, 2003. jan. 29-31. pp. 10-13. 

FARKASNÉ SZERLETICS A. 2003. A tápanyagellátás jelentısége a gyomszabályozásban 

(Importance of nutrition in the weed management). III. Növénytermesztési 

Tudományos Nap, Gödöllı, 2003. máj. 15. Kiadvány (szerk. Csorba Zs., Jolánkai 

P., Szöllısi G.), pp. 49-53. 

FARKASNÉ SZERLETICS A. 2004. Mővelés okozta talajállapotváltozás és gyomosodás 

összefüggése száraz évjáratban, ıszi búzában. MTA-AMB Kutatási és Fejlesztési 

tanácskozás, Gödöllı, 2004. jan. 20-21. 3. kötet, p. 82-86. 

FARKASNÉ SZERLETICS A. 2004. Mővelés, talajállapot és gyomosodás összefüggései 

olajretek köztes növényben, gödöllıi termıhelyen. Keszthelyi Növényvédelmi 

Fórum, 2004. jan. 28-30. p. 9-11. 

FARKASNÉ SZERLETICS A. 2004. Kettıs termesztés, köztes termesztés, köztes növény 

elnevezések és használatuk. XLVI. Georgikon Napok, Keszthely, 2004. szept. 16- 

17. CD kiadvány, ISBN 963 9096 962 

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erdıtalajon. XLVI. Georgikon Napok, Keszthely, 2004. szept. 16-17. CD kiadvány, 

ISBN 963 9096 962 

30

Herbologia Vol. 7, No. 1, 2006. 

RESISTANCE STUDY OF AMARANTHUS RETROFLEXUS L. SPECIES 

POPULATION TO THE HERBICIDE IMAZETHAPYR 

Branko Konstantinović, Maja Meseldžija, Dragana Šunjka 

Faculty of Agriculture, Trg Dositeja Obradovica 8, Novi Sad, Serbia and Montenegro 

E-mail: maja@polj.ns.ac.yu 

Abstract 

Use of herbicides and lack of alternative methods of weed control in 

conditions of intensive agricultural production have created convenient 

environment for herbicide resistant weed species development. Permanent 

use of herbicides belonging to the group ALS inhibitors, especially 

imidazolinones and sulfonylureas, led to resistance occurrence of weed 

species to this herbicide group. 

During two years (2005-2006) resistance of weed species Amaranthus 

retroflexus L. to ALS inhibitors was studied. From different localities in 

Vojvodina, i.e. Krivaja, Kikinda and Becej, with a long history of ALS 

inhibitors use in weed control, seed of plants for which there exist possibility 

of resistance occurrence to herbicide imazethapyr was collected. Studies were 

performed by two methodic procedures, by Petri dish assays (Clay and 

Underwood, 1990) and by whole plant studies (Moss, 1995). In the trials, as a 

susceptible standard herbicide free population of Amaranthus retroflexus L. 

from ruderal sites that was used. Results of the assay are given in the reaction 

curve, and resistance index is determined in regard to the susceptible referent 

population. 

By comparative analysis, resistance occurrence of weed biotype 

Amaranthus retroflexus L. from the locality Krivaja has been established, 

whereas populations from localities Becej and Kikinda remained susceptible 

to the mode of action of the studied herbicide belonging to the ALS inhibitor 

group. 

Key words: Amaranthus retroflexus L., ALS inhibitors, imazethapyr, herbicide resistance. 

Introduction 

Nowadays herbicides belonging to the group of ALS inhibitors such 

as sulfonylureas, imidazolinones, triazolopyirimidines, pyrimidinylthiobenzoates 

and sulfonylamino-carbonil-triazoles represent extremely 

significant herbicides for weed control in many crops (Wagner et al., 2002). 

Their permanent use during three years period, or longer, resulted in 

evolution of ALS resistant biotypes in the world (Thill et al., 1991; Powles

B. Konstantinović et al. 

and Shaner, 2001; Rashid et al., 2003; Rubin et al., 2004) and in Vojvodina 

(Konstantinovic et al., 2003a; 2003b; 2003c). 

Primary action target site of these herbicides is the enzyme of 

acetolactate synthase that participate in biosynthesis of amino acids 

isoleucine, leucine and valine (Ray, 1984; Gerwick et al., 1990; Takahashi et 

al., 1991, Babczinski, 2002), and resistance develops as the consequence of 

the single mutation points that ALS structure makes less susceptible to 

herbicides. 

After five years of permanent use of the ALS inhibiting herbicides in 

monoculture of Triticum aestivum L. crop (Mallory-Smith et al., 1990) in 

1987 the first weed resistant to ALS inhibitors, Lactuca serriola (Smith and 

Cairns, 2001) was determined. Stellaria media (L.) Vill (Kudsk et al., 1995) 

was the first weed species resistant to Sulfonylureas found in Europe. Until 

now, resistance has been described for 93 weed biotypes from all over the 

world, and this number is constantly increasing (Heap, 2006). In regard to the 

other herbicide groups, weed biotypes resistant to herbicide that inhibit ALS 

enzyme are the most numerous. 

In the paper the occurrence of herbicide resistance development of the 

weed species Amaranthus retroflexus L. from various localities in Vojvodina 

to herbicide imazethapyr from the chemical family Imidazolinones. On the 

studied localities Imidazolinones had long history of use in weed control. 

Material and methods 

During 2005 and 2006 study of weed species Amaranthus retroflexus 

L. resistance to imazethapyr was performed according to the methods applied 

in laboratory conditions and climatic chamber (Clay and Underwood, 1990; 

Moss, 1995). In bioassays a range of imazethapyr rates were used, e.g. 0 , 

0.04 , 0.08 , 0.10 , 0.15 , 0.20 and 0.40 kg a.i./l. During assays seedling 

epicotyls and hypocotyls length, stem height, foliage fresh weights and seed 

germination and shooting were measured. Statistical data processing was 

performed by variance analysis (ANOVA), and significant difference was 

evaluated by t-test (Hadzivukovic, 1991). Resistance can be determined only 

if there are statistically significant differences between the studied population 

and the susceptible standard and if resistant population can not be controlled 

by herbicide rate that is efficient in control of the susceptible one (Beckie et 

all., 2000). Results of the measured parameters – epicotyls and hypocotyls 

length, stem height and germination percentage and shooting are presented as 

a quantity-response curve, while values of the foliage fresh weight and 

resistance indices were given in a table. 

32

Resistance study of A. retroflexus L. species population to the herbicide imazethapyr 

Results 

Statistical analysis results of epicotyls and hypocotyls shoots length, 

stem height and foliage fresh weight (t test) are given in Table 1. Analysis of 

imazethapyr effect to the measured biological parameters of the species 

Amaranthus retroflexus L. showed that there are statistically significant 

differences (p< 0.05) between values of the measured parameters of 

populations from locality Krivaja and population used as a susceptible 

standard (S). 

Tab. 1. Significant difference between Amaranthus retroflexus L. populations 

from the studied localities and susceptible standard treated by imazethapyr 

Localities 

Parameters 

Hypocotyl 

length 

Stem 

height 

Foliage 

fresh 

weight 

Epicotyl 

length 

Krivaja - S * * * * 

Kikinda - S N.Z. N.Z. N.Z. N.Z. 

Bečej - S N.Z. N.Z. N.Z. N.Z. 

p


Amaranthus retroflexus L. seed germination 

Effect of the herbicide imazethapyr to seed germination of weed 

species Amaranthus retroflexus L. is given in the Graph 1. The highest 

percentage of germinated seeds was established for population from locality 

Krivaja. Population of the susceptible standard and localities Kikinda and 

Becej had very low germination capability with all applied herbicide rates. 

duzina epikotila (mm) 

epycotyl length (mm) 

25 

20 

15 

10 

5 

0 

0 

0.04 

0.08 

0.1 

0.15 

0.2 

0.4 

kg a.m. imazetapir/l 

kg. a.i. imazethapyr/l 

Krivaja 

Kikinda 

Bečej 

Ruderalno 

staniste/ruderal 

site 

Fig. 2. Effect of the herbicide imazethapyr to Amaranthus retroflexus 

L. epycotyl seedlings length 

34


duzina hipokotila (mm) 

hypocotyl length (mm) 

20 

15 

10 

5 

0 

0 0.04 0.08 0.1 0.15 0.2 0.4 


kg a.i. imazethapyr/l 

Krivaja 

Kikinda 

Bečej 

Ruderalno 

staniste/ruderal site 

Fig. 3. Effect of the herbicide imazethapyr to Amaranthus retroflexus 

L. hypocotyl seedlings length 

By statistical analysis (Table 1) of the values for epicotyls and 

hypocotyls length, significant difference was determined for populations 

from locality Krivaja in regard to the other studied localities and population 

of the susceptible standard. Populations values from localities Kikinda and 

Becej did not show significant differences from those obtained for the 

susceptible standard. Values for epicotyls and hypocotyls length are 

presented in Graphs 2 and 3. 

procenat nicanja 

% of shooting 

120 

100 

80 

60 

40 

20 

0 

0 0.04 0.08 0.1 0.15 0.2 0.4 



Krivaja 

Kikinda 

Bečej 

Ruderalno 


Fig. 4. Effect of the herbicide imazethapyr to shooting of 

Amaranthus retroflexus L. plants 

35


Effect of the herbicide imazethapyr to shooting of plants is given in 

Graph 1. Percentage of emerged plants from the site Krivaja was the highest. 

visina stabla (mm) 

stem height (mm) 

35 

30 

25 

20 

15 

10 

5 

0 

0 0.04 0.08 0.1 0.15 0.2 0.4 



Krivaja 

Kikinda 

Bečej 

Ruderalno 


Fig. 5. Effect of the herbicide imazethapyr to the height Amaranthus 

retroflexus L. stems. 

Values of the studied parameters of Amaranthus retroflexus L. 

biotype plants from locality Krivaja showed statistical significant difference 

(p< 0.05) in regard to the susceptible standard and other studied localities. 

Between biotypes from localities Kikinda and Becej there were no 

statistically significant differences, nor there were differences in regard to the 

susceptible standard (Graph 4). 

Resistance level based upon foliage fresh weight was determined 

according to the scale by Moss et al (1999) that imply several possible 

resistance levels of the studied population (Table 2). 

Tab. 2. Resistance level of the studied populations of Amaranthus 

retroflexus L. determined according to the scale by Moss, based upon 

the fresh weight. 

Locality Resistance level 

Krivaja 4* 

Kikinda 1* 

Bečej 

S 

S - osetljivost na primenjeni herbicid/susceptibility to the applied herbicide 

1* – rana indikacija rezistentnosti, mogućnost da je došlo do redukcije delovanja 

herbicida/early indication of the resistance, suspected herbicide reduction 

36


2*/3* - potvrñena rezistentnost, mogućnost da je došlo i do redukcije delovanja 

herbicida/confirmed resistance, suspected herbicide reduction 

5*/4* - potvrñena rezistentnost, mala verovatnoća lošeg delovanja herbicidacomfirmed 

resistance/reduced likelihood of low herbicide action. 

Tab. 3. Resistance level of the studied populations of Amaranthus 

retroflexus L. given in resistance index 

Resistance index 

Locality epicotyl hypocotyl stem height foliage fresh weight 

Krivaja 1.8 1.61 1.0 2.27 

Kikinda 1.0 0.8 0.9 0.53 

Bečej 1.0 1.0 1.0 0.99 

The highest values of resistance index of the measured parameters 

were determined for population from the locality Krivaja (1.0 – 2.27). The 

values of resistance index for population of Amaranthus retroflexus L. from 

localities Kikinda and Becej were significantly lower, i.e. less than 1. 

Discussion 

Determined significant differences in germination (Fig. 1) and values 

for epicotyls and hypocotyls length (Fig. 2 and 3) between biotype from 

locality Krivaja and susceptible standard, as well as other studied localities 

implied high resistance of this biotype to the herbicide imazethapyr. It was 

also determined that decay of seedlings from localities Kikinda and Becej 

occurred at rates above 0.08 kg a.i. imazethapyr/l, while seedlings from 

localities Krivaja at rate of 0.40 kg a.i. imazethapyr/l remained well 

developed. Seedlings from ruderal site, used as the susceptible standard 

completely decayed at a rate of 0.04 kg. a.i. imazethapyr/l. 

In regard to susceptible standard and localities Kikinda and Becej, 

increased rates of the applied herbicide caused the lowest reduction in 

epicotyls and hypocotyls length of weed species Amaranthus retroflexus L. 

biotype from locality Krivaja. 

Imazethapyr effect to weed species Amaranthus retroflexus L. 

biotypes evinced in differences in plant emergence and stem height (Fig. 4 

and 5). In all applied imazethapyr rates, the highest percentage of emerged 

plants (100%), as well as the highest values for the stem height was 

determined for biotype from locality Krivaja. Decay of plants from this 

locality did not occur even with applied rate of 0.40 kg a.i. imazethapyr/l. 

Based upon measured biological parameters, samples of the susceptible 

standard, as well as plants from localities Kikinda and Becej, remained 

37


susceptible to herbicide imazethapyr action, for decay occurred after 

application of the second rate of 0.08 kg a.i. imazethapyr/l. 

Based upon resistance level obtained by foliage fresh weight 

measurement (Table 2), resistance was confirmed for populations from 

locality Krivaja (4*), with a slight probability that herbicide showed low 

efficiency. For biotype from locality Kikinda an early indication of resistance 

was determined, but with a possibility of herbicide efficiency reduction. 

Population from locality Becej remained susceptible to the applied herbicide. 

Resistance index of all measured parameters (Table 3) suggests that 

biotype from the locality Krivaja acquired the highest resistance to the 

applied rates of the herbicide imazethapir. Populations from locality Becej 

(IR = 0.99 - 1) and Kikinda (IR = 0.53 – 1) showed high susceptibility to 

herbicide imazethapyr. 

Conclusion 

Based upon results of the resistance studies of different populations 

of the weed species Amaranthus retroflexus L. to herbicide imazethapyr, it 

can be concluded that intensive use of ALS inhibiting herbicides caused 

reduced susceptibility of weed species Amaranthus retroflexus L. population 

to imazethapyr. The biotype from the site Krivaja showed the highest 

resistance to the applied rates of herbicide imazethapyr. Biotype from the 

locality Becej showed reduced susceptibility to the applied herbicide (RI = 

0.99 – 1.0). The highest susceptibility to the applied rates of the herbicide 

imazethapyr was found in the biotype from Kikinda (RI = 0.53 – 1.0). 

References 

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istraživanjima. Poljoprivredni fakultet, Novi Sad. 

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www.weedscience.com 

KONSANTINOVIĆ, B., MESELDŽIJA, M., ŠUNJKA, D., KONSTANTINOVIĆ, BO. (2003a): 

Determination of resistant biotypes of Amaranthus retroflexus L. on ALS inhibitors. 

3 rd International Plant Protection Symposium at Debrecen University, Debrecen 

Hungary, p. 269-276. 

38


KONSTANTINOVIĆ, B., MESELDŽIJA, M., POPOVIĆ, S., KONSTANTINOVIĆ, BO. (2003b): Study 

of resistance to ALS inhibitors in the weed species Echinochloa crus-galli L., The 

BCPC International Congress, Glasgow, Scotland, UK, Vol. 2, p. 771-775. 

KONSTANTINOVIĆ, B., MESELDŽIJA, M., ŠUNJKA, D. (2003c): Ispitivanje rezistentnosti 

korovske vrste Echinochloa crus-galli L. na ALS inhibitore, Zbornik referata 2. 

savetovanja o korovima, Sarajevo, 6-7 juni 2003. 

KUDSK, P., MATHIASSEN, S.K. AND COTTERMAN, J.C. (1995) Sulfonylurea resistance in 

Stellaria media (L.) Vill. Weed Research, 35, p. 1924. 

MALLORY-SMITH, C.A., THILL, D.C.& DIAL, M.J. (1990): Identification of sulfonilurea 

herbicide-resistant prickly lettuce (Lactuca seriola). Weed Technology, 4, p. 163- 

168. 

MOSS, S.R. (1995): Techiniques for determinig herbicide resistance. Proceedings of the 

Brighton Crop Protection Conference-Weeds, p. 547-556. 

POWLES, S. B. & SHANER, D.L. EDS. (2001): Herbicide resistance in world grains. CRC 

Press, Boca Raton, Florida, USA. p. 308. 

RASHID, A., NEWMAN, J.C., O'DONOVAN, J.T., ROBINSON, D., MAURICE, D., POISSON, D. AND 

HALL, L.M. (2003): Sulfonylurea herbicide resistance in Sonchus asper biotypes in 

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inhibitors of acethydroxyacid synthase. Plant Physiology, 76, p. 545-546. 

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39


INFLUENCE OF THE ADJUVANT DESH ON THE EFFICACY AND 

SELECTIVITY OF IMAZAMOX 40 a.i.L -1 (PULSAR 40) IN THREE 

PERENNIAL LEGUME CROPS 

Tsvetanka Dimitrova 1 , Senka Milanova 2 

1 Institute of Forage Crops, 5800 Pleven ifc@el-soft.com 

2 Institute of Plant Protection, 2230 Kostinbrod protection@infotel.bg 

Abstract 

During the period 2003-2005 a study was conducted on slightly 

leached chernozem with the purpose of studying the influence of the adjuvant 

Desh on the efficacy and selectivity of Imazamox 49 a.i.L -1 (Pulsar 40) in 

lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and 

sainfoin (Onobrychis vicifolia Scop.). It was found that: 

The herbicide Imazamox 40 a.i.L -1 (Pulsar 40) at the rate of 20 ml 

a.i.ha -1 in combination with the adjuvant Desh – 1000 ml a.i. ha -1 applied in 

early growing season of lucerne, birdsfoot trefoil and sainfoin had high 

selectivity and herbicidal efficacity reaching 93-97%; 

Treatment of swards of perennial legume crops improved their 

botanical composition and increased dry biomass productivity 1.4 to 2.8 

times. 

Key words: Imazamox 40 a.i.L -1 , adjuvant Desh, weeds, productivity, perennial legume 

crops. 

Introduction 

Economic importance of the perennial legume crops including lucerne 

(Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin 

(Onobrychis vicifolia Scop.) is many-sided. They are valuable for the high 

biological value of their forage, as well as in an ecological aspect improving 

soil fertility and phytosanitary state. 

Weed competition is one of the main factors causing quick thinning 

of the swards of these species, reducing and worsening quality of their 

production. This circumstance is of decisive importance for weed control 

during the period after establishment of the stands of these herbaceous 

species. 

Although the chemical method of controlling weeds in the swards of the 

above-mentioned species is considered efficient by some authors, the studies 

are limited in this field (Benkov & Prodanov, 1975; Dimitrova, 1987 and 

1995; Lescar Audy, 1971). 

The out-of-vegetation treatment of lucerne with Imazethapyr 100

Tsvetanka Dimitrova and Senka Milanova 

a.i.L -1 (Speed 10 SL) resulted in 90.8 % biological efficacy, increase of dry 

biomass and crude protein yield of 60 % and 2.4 to 2.6 % respectively and 

decrease of fibre content of 3.8 to 4.1 % (Dimitrova, 2001). The chemical 

weed control proved to be the most efficient in pure lucerne growing for 

forage, the net income of its application increasing by 64.8 % (Stoykova & 

Dimitrova, 2005). 

The long and unilateral use of the same herbicides resulted in 

selection of genetically resistant weeds (Nikolova & Konstantinov, 1989; 

Beckie et al., 2000; Lee & Owen, 2000). Resistance has been reported for 

most herbicide categories and at least for 174 weed species (Heap, 2004). 

This circumstance necessitates study of new approaches to using herbicides, 

new active substances, optimimization of their doses. Some authors reported 

that the adjuvants to the herbicidal solutions led to an increase of their 

efficacy and to reduction of the doses (Kudsk & Streibig, 2002; Dogan et al., 

2002). 

Imazamox belongs to the imidazolinone class that includes imazapyr, 

imazapic, imazethapyr, imazamox and imazametabenz. The herbicides of the 

group of imidazolinones and sulphonylureas kill the weeds by inhibiting 

acetolactate synthase (ALS). The imidazolinone herbicides possess high 

biological efficacy at low application rates and are an attractive alternative 

for weed control in lines of spring wheat resistant to the imidazolinone group 

(Pozniak et al., 2004), winter wheat (Stougaard et al., 2004). Resistance to 

imazamox has also been introduced into cultivated sunflower by traditional 

breeding methods (Massinga et al., 2005). Herbicide-resistant rape prevails 

on the rape market in Canada with imidazoline-resistant canola (IPI) with 

50:50 combination of imazamox and imazethapyr (Karker et al., 2004). Due 

to the great biological activity of imazamox it is very important to know the 

possibility for dose decrease. The interest for application of reduced rates of 

herbicides is in favor of the farmers and environment. The adjuvants can 

stimulate the herbicide uptake and provide a possibility for dose reduction 

(Mathiassen & Kudsk, 2002; Kieloch & Domaradzki, 2005). 

The objective of this study was to investigate the influence of the 

adjuvant Desh on the efficacy and selectivity of Imazamox 40 a.i.L -1 (Pulsar 

40) in lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) 

and sainfoin (Onobrychis vicifolia Scop.). 

Material and methods 

The study was conducted during the period 2003-2005 at the 

experimental field of the Institute of Forage Crops in Pleven on slightly 

leached chermozem. The variants presented in Table 1 were laid out three 

times by years in established stands of lucerne, birdsfoot trefoil and sainfoin. 

42

Influence of the adjuvant Desh on the efficacy and selectivity of imazamox 40 a.i. l -1 (Pulsar) 

The block method was used with three replications and harvest plot size of 20 

m 2 . 

Natural background of weed infestation was used. The predominant 

weed species were also main weeds in the old swards of the above-mentioned 

crops: Capsella bursa pastoris L., Thlaspi arvense L., Stellaria media L., 

Veronica hederifolia L., Anagalis arvensis. 

The treatment was made with 400 l ha -1 working solution in early 

growing season. The adjuvant Desh was added immediately before the 

treatment. The following characteristics were observed: selectivity (after 

EWRS scale); degree of weed infestation (by the quantity and quantityweight 

method); herbicidal efficacy, %; dry biomass yield mathematically 

processed by the method of variance analysis. 

During the three study years the results of the observed characteristics 

retained their trend among the variants which allowed their presentation on 

average for the experimental period. 

Results and discussion 

The herbicide Imazamox applied alone or with the adjuvant Desh 

possesses high selectivity to lucerne, birdsfoot trefoil and sainfoin. It belongs 

to the group of wide-spectrum herbicides with phytotoxic action to the annual 

mono- and dicotyledonous weeds. Under the trial conditions Capsella bursa 

pastoris L. and Thlapsi arvense L. showed high susceptibility; they are also 

the main weeds of the old stands of the studied species. Our observations 

showed complete killing of the weeds that were at earlier stages of their 

development (seedlings and rosette) at the moment of treatment. The weeds 

that were at a more advanced stage remained chlorotic and formed no flowerbearing 

stems. In view of the circumstance that in these stands a considerable 

part of the weeds wintered successfully, the timely treatment at the first 

opportunity in spring was a necessary condition of reaching high herbicidal 

efficacy. 

The herbicidal efficacy (Table 2) with regard to the weed weight in 

the standard and Imazethapyr reached 96-98% in different crops. The values 

for Imazamox at the rate of 20 ml a.i.ha -1 

with the adjuvant Desh at the rate 

of 1000 ml ha -1, being within the range of 93-97 %, were the closest to these. 

When comparing this efficacy with that for the application of the herbicide 

alone it was evident that owing to the adjuvant Desh it was higher by 17 to 

19%. The synergistic action of the activating additives was also reported by 

other authors who explained it by an increase of the retention and absorption 

of the herbicidal solution by the leaves (Borona et al., 2003; Woznica, 2005). 

At the lower dose of the adjuvant of 500 ml ha -1 

the herbicidal efficacy 

43


increased by 9 to 10% as compared to its application alone. The results 

showed a unsatisfactory herbicidal effect (71-79%) when applying the 

herbicide alone (V 3 ), as well as when applying it with the adjuvant Desh at 

the lower doses (V 6 ). 

The removal of the competitive effect of the weeds led in an increase 

of the participation of the cultivated components in the swards of the 

perennial legume crops and as a result the dry biomass productivity also 

increased (Table 3). This increase was 2.4 to 2.8 times in the treated lucerne 

stands and 1.1 to 1.4 times in birdsfoot trefoil and sainfoin. 

The highest yields of dry biomass, close to those of the weeded check 

and the standard, were harvested from the lucerne, birdsfoot trefoil and 

sainfoin stands treated with Imazamox + Desh at the rates of 20 + 1000 ml 

a.i.ha -1 

reaching 4700, 2690 and 6350 kg ha -1 , respectively. The differences 

in the absolute values of the dry biomass yields had very good positive 

significance. 

Tab. 1. Trial variants 

Variant* Rate, ml a.i.ha -1 

V 1 – Check – zero - 

V 2 – Imazethapyr 100 a.i.L -1 (Pulsar 100SL)-standard 40 

V 3 – Imazamox 40 a.i.L -1 (Pulsar 40) 20 

V 4 – Imazamox 40 a.i.L -1 (Pulsar 40)+Desh (adjuvant) 20+500 

V 5 – Imazamox 40 a.i.L -1 (Pulsar 40)+Desh 20+1000 



V 8 – Check – weeded - 

*The variants of V 1 to V 8 were laid out in three perennial legume crops: lucerne (Medicago 

sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin (Onobrychis vicifolia Scop.) 

Tab. 2. Efficacy of Imazamox 40 a.i.L -1 (Pulsar 40) in perennial legume crops 

Lucerne 

Birdsfoot trefoil 

Sainfoin 

Variant 

(Medicago sativa L.) (Lotus corniculatus L.) (Onobrychis vicifolia Scop.) 

Weeds/m 2 Weeds/m 2 Weeds/m 2 

number weight,g HE*,% number weight,g HE*,% number weight,g HE*,% 

V 1 534 655 - 322 679 - 280 590 - 

V 2 10 15 98 12 28 96 6 12 98 

V 3 143 161 76 97 175 74 73 125 79 

V 4 26 94 86 59 115 83 25 67 89 

V 5 12 31 95 27 49 93 9 19 97 

V 6 144 169 74 103 199 71 81 141 76 

V 7 104 101 85 65 129 81 38 78 87 

44

Influence of the adjuvant Desh on the efficacy and selectivity of imazamox 40 a.i. l -1 (Pulsar) 

HE* - herbicidal efficacy 

Tab. 3. Influence of the treatment with Imazamox 40 a.i.L -1 (Pulsar 

40) on dry biomass productivity of perennial legume crops 

Dry biomass 

Variant Lucerne 

(Medicago sativa L.) 

Birdsfoot trefoil 

(Lotus corniculatus L.) 

Sainfoin 

(Onobrychis vicifolia Scop) 

kg/ha -1 %V 1 kg/ha -1 %V 1 kg/ha -1 %V 1 

V 1 1680 100 1820 100 4310 100 

V 2 4810 286 2770 152 6350 147 

V 3 4210 250 2150 118 5010 116 

V 4 4450 265 2370 130 5530 128 

V 5 4700 280 2690 148 6350 147 

V 6 4150 247 2130 117 4920 114 

V 7 4330 258 2260 124 5230 121 

V 8 4920 293 2860 157 6430 149 

GD P 5% 68,7 140,2 135,1 

P 1% 95,4 194,7 187,5 

P 0,1% 132,7 270,7 260,8 

Conclusion 

The herbicide Imazamox 40 a.i.ha -1 (Pulsar 40) at the dose of 20 ml 

a.i.ha -1 in combination with the adjuvant Desh at 1000 ml a.i.ha 

-1 applied in 

early growing seasonon of lucerne, birdsfoot trefoil and sainfoin had high 

selectivity and herbicidal efficacy reaching 93-97%; 

Treatment of swards of perennial legume crops improved their 

botanical composition and increased dry biomass productivity 1.4 to 2.8 

times. 

Reference 

BENKOV, B., I.PRODANOV, (1975): In: Chemical weed control, Zemizdat, Sofia. 

DIMITROVA, TS., (1987): Influence of weeds and their control on forage yields and sward 

botanical composition of pure and mixed birdsfoot trefoil stands, Plant Science, 

XXIV, 1, 65-68. 

DIMITROVA, TS., (1995): Study of the influence of growing method and weed control on 

the degree of weed infestation and seed yield of sainfoin, Contemporary Plant 

Protection (Proc. Papers, October 1995), Sofia, 462-466. 

DIMITROVA, TS., (2001): Biological study of the herbicide Speed 10SL (Imazethapyr 

100g/l) under out-of-vegetation treatment of lucerne (Medicago sativa L.), Proc. 

Scientific Works of AU – Plovdiv, vol. XLVI, No.2, 205-208. 

NIKOLOVA, V., K.KONSTANTINOV, (1989): Study of compensation changes of weed 

associations in vegetable crops and potatoes – a basis for accurate prognosis and 

efficient control, Proc. Plant Protection in Aid of Agriculture, Proc. IPP, USWB, 

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Sofia, 225-245. 

STOYKOVA, M., TS.DIMITROVA, (2005): Comparative economic analysis of efficiency 

of the plant protection practices used in lucerne forage production, Agricultural 

Economics and Management, 50, 4, 54-58. 

BECKIE, H. I., HEAP,I..M., SMEAA, R.I., HALL, L. M., (2000): Screening for herbicide 

resistance in weeds, Weed Technology, 14 (2) 428-445. 

BORONA, VL., V.ZADOROZHNY,T. POSTOLOVSKAY, (2003): The influence of 

adjuvant on the efficacy of graminicides in soybeans and nicosulfuron in maize, 

Herbologija, vol. 4, № 1, 151-155. 

DOGAN, M.N., BOZ,O., ALBAY, F., (2002): Influence of some additives on the efficacy of 

nicosulfuron in maiz and fenoxa-prop-P-ethyl in wheat, Proc. 12 th EWRS 

Symposium, Wageningen (The Netherlands), 94-95. 

HARKER, K., G. CLAYTON, J. O’DONOVAN, R. BLACKSNAW, F. STEVENSON, 

(2004). Herbicide timing and rate effects on weed management in three herbicide – 

resistant canola systems. Weed Technology, 18, 4, 1006-1012. 

HEAP, I., (2004): International Sulvey of herbicide - resistant weed. http: www weed 

science. org. Accessed 22 November, 2004. 

KIELOCH, R., K. DOMARADZKI (2005): The influence of relative humidity on Anthemis 

arvensis and Stellaria media control by tribenuron - methyl used alone and with 

adjuvants. 13 th EWRS Symposium, Bari, Italy, CD – ROM. 

KUDSK, P., STREIBIG, I.C., \2002|: Herbicides-a double – edged sword Proc. 12 th 

EWRS Symposium, Wageningen (The Netherlands), 94-95. 

LEE, I.M., OWEN, M.D., (2000): Comparison of acetolactate synthase enzyme inhibition 

amond resistant and susceptible Xanthium strumarium biotypes, Weed Science, 48 

(3) 286-290. 

LESCAR, L., AUDY, (1971): Comptes rendus des journees d’etudes sur les herbicides, t. 4. 

COLUMA. 

MASSINGA, R., K. AL-KHATIB, P. ST. AMAND, J. MILLER (2005): Relative fitness of 

imazamox resistant common sunflower and prairie sunflower. Weed Science, 53, 2, 

166-174. 

MATHIASSEN, S., PER KUDSK (2002): The influence of adjuvants on the efficacy and 

rainfastness of iudosulfuron. 12 th EWRS (European Weed Research Society) 

Symposium 2002, Wageningen, 206-207. 

POZNIAK, C., F. HOLM, R. HUCL (2004): Field performance of imazamox – resistant 

spring wheat. Canadian Journal of Plant Science, 84, 4, 1205-1211. 

STOUGAARD, R., C. MALLORY – SMITH, J. MICKELSON (2004): Downy brome 

(Bromus tectorum) response to imazamox rate and application timing in herbicide – 

resistant winter wheat. Weed Technology, 18, 4, 1043-1048. 

WOZNICA, Z., (2005): Recent advances in adjuvant formulation thechnology, 13 th EWRS 

Symposium, Bari – Italy, CD – ROM 

46


HERBICIDE-RESISTANT CROPS - ADVANTAGES AND RISKS 

Zvonko Pacanoski 

Faculty for Agricultural Sciences and Food, 1000 Skopje, R. Macedonia 

zvonkop@zf.ukim.edu.mk 

Abstract 

Revealing of genetically modified, herbicide-resistant crops (HRCs) 

at the end of the 20 th century brought many controversies. At one side, HRCs 

enable the farmers to more effectively use reduced or no-tillage cultural 

practices, eliminate of troublesome weeds resistant to some herbicides, using 

nonselective herbicides, usually glyphosate and glufosinate as 

“environmentally friendly” herbicides, decrease of expenses for crop 

production, and finely, more economically and effectively manage of weeds. 

At the other side, there is fear of possibile developing of weed resistant to 

non-selective herbicides, appearance of volunteer HR crops, invasion of the 

environment beyond the farm boundary, influence of HRCs to biodiversity, 

exchange of genetic material between related HRCs and wild progenitors, 

conventional crops, and weeds. The coming period should clarify the 

eventual impact of these powerful new tools on weed science, weed 

management, environment and human health. 

Keywords: Genetically modified organisms (GMOs), herbicide-resistant crops 

(HRCs), glyphosate, glufosinate, weeds 

Introduction 

Weed control obtained a new dimension with recent revealing and 

practical application of plant growth regulators. From that moment chemical 

industry in collaboration with science have focused on creation of new 

herbicide active ingredients with large efficacy, selectivity and possibility for 

use in all crops against almost all weed species. In that period has developed 

opinion that weed problem would be dissolved forever, without investing 

efforts in finding and development alternative methods for weed control. 

However, a long period did not pass when the first problem appeared - 

resistance of some weeds to some herbicides, on which, until that moment the 

weedd had been susceptible. The number of resistant weeds to some 

herbicides continuously have increased. According HRAC and WSSA, about 

182 weed species worldwide (109 broad-leaved and 73 grass weeds) 

developed resistance to large number of different herbicides from all mode of 

action groups. In the beginning, increasing the herbicides rate was one of

Z. Pacanoski 

possible solution for this problem. However, the success was of short 

duration and partial, but harms were double. Namely, after certain period the 

resistance appeared again, and first environment damages concerning 

pollution of the soil, surface and underground water. Some widely used 

herbicides were out of use and forbidden, but weed problem stay remained. 

Science and chemical industry were faced with challenge to find alternative 

ways in combating weeds. Many of them (biological, physical, alellopathy) 

gave insufficient results, and they are not adequate substitute for herbicides. 

Recently, in the solving on this problem, biotechnology with genetic 

engineering were involved. Scientists are now creating new plants, in order 

to fight weeds more simpler, cheaper, and at the same time, to stop pollution 

of environment. All these points of view and principles are taken into 

consideration in creating of genetic modified organisms (GMOs) 

The aim of this review is to give some information about GMOs, 

particularly HRCs, their advantages, disadvantages and risks for plant 

biodiversity. 

From the moment creating GMOs to the time of their marketing 

(1995), short period passed, but their planted area year after year have been 

increasing. According Berca (2004), GMOs are cultivated 12% more in 2002 

compared to 1995, 15% more in 2003 compared to 2002, respectively. 

According to ISAAA, sowings of GM crops rose to 81 million hectares in 

2004 recording a 20 percent increase over 2003. 

Generally, GM crops are planted in 18 countries, at about 10 million 

farms. The biggest producers of GMOs (James, 2003) are: USA, Canada, 

Argentina, Brazil, and China. These countries account to about 98% of all 

world GMOs production. 

Tab. 1. The biggest world producers of GMO in the world (James, 2003) 

Country Surface mil. ha % of total 

cultivated GMO 

USA 42,8 63 

Argentina 13,9 21 

Canada 4,4 6 

Brasil 3,0 4 

China 2,8 4 

Tab. 2. Distribution of GMO on products (James, 2003) 

Crops Surface mil. ha % of total 

cultivated GMO 

Soya 41.7 61 

48

Herbicide-resistant crops – advatages and risk 

Maize 15.5 23 

Cotton 7.2 11 

Canola 3.6 5 

Advantages of herbicides resistant crops 

About 71% (more than 40 million hectares) of total cultivated GMOs 

in the world are herbicides resistant crops (HRCs). The reason why the 

biggest percent of GMOs are HRCs lie in the numerous advantages of this 

new technology in weed control. One of the main benefits is the possibility of 

controlling a range of broad-leaves and grass weeds with one or two 

properly timed application of glyphosate (Baldwin, 1999). Conventional 

herbicide method required applications of two or more different herbicides. 

In addition, conventional herbicide programme is tightly connected with crop 

and weed growth stages, also with ecological conditions (climate and soil). 

Taking into consideration all these factors, possibility for potentional crop 

injury are high (Johnson et al., 2002). Cultivating transgenic crops enable 

using nonselective herbicides, usually glyphosate and glufosinate, usually 

once, but in some cases two applications of these herbicides controlled 

weeds. At the same time, application period is more flexible than in 

conventional way; it does not depend of growth stages of crops and weeds, 

while the possibility for injury crop is minimal (Carpenter and Gianessi, 

1999). 

Utilization of new method of weed management reduces application 

of long-term residual herbicides, that are, according to new environmental 

standards, unacceptable (Shaw et al., 2001). New weed management 

technology is particularly applicable in the places with weeds dominant 

resistant to some selective herbicides. In these circumstances, glyphosate and 

glufosinate are a good solution for this problem, because efficacy of these 

herbicides is very high. One of these herbicides is capable, alone, to solve the 

weed problem, even better than standard combination of two or three 

selective herbicides. 

Numerous investigations confirmed excellent results in efficacy of 

new way of weed control, which is usually more than 95%. Since neither 

glyphosate nor glufosinate have residual activity after their application, 

second application, if necessary, is possible for achieving weed-free crops. 

The other major advantage of using glyphosate and glufosinate in 

HRCs is their role in no-till and zero-till agriculture. Minimizing or 

eliminating soil tillage reduces or prevents soil erosion, humus degradation 

and destruction of soil structure. However, the weeds soon become main 

problem in such a system if previous mentioned herbicides are not used. 

49

Z. Pacanoski 

In context of this thesis are farmer’s reactions cultivating transgenic 

maize and soybean resistant to glyphosate and glufosinate under no-till 

conditions. Their reactions are mainly positive and they confirm that using 

transgenic crops give bigger opportunities in better weed management system 

with lower herbicide inputs. 

Beside excellent efficacy in weed control, glyphosate is 

environmentally friendly herbicide. After glyphosate is applied to forests, 

fields, and other land by spraying, it is strongly adsorbed to soil, remains in 

the upper soil layers, and has a low propensity for leaching. Glyphosate 

readily and completely biodegrades in soil. Its average half-life in soil is 

about 60 days; main product of its degradation is aminomethylphosphoric 

acid, which is broken down further by soil microorganisms as well. 

Glyphosate is practically non-toxic for birds, mammals and bees (LD 50 for 

rats is 5600 mg/kg. Oral LD 50 for rabbits and goats is more than 10,000 

mg/kg) 

Similar is the situation for glufosinate, as nonselective contact and 

nonpersistent herbicide with moderate leaching. Glufosinate is also 

environmentally friendly and practically non-toxic (oral LD 50 above 2000 

mg/kg and dermal 4000 mg/kg). It has no residual activities and does not 

inflict restriction to crop rotation. Half-life is about 40 days. 

Toxicity 

category 

Tab. 3. Ecotoxicological categories 

Mammalian 

(acute oral)* 

mg/kg 

Avian 

(acute oral)* 

mg/kg 

Avian 

(dietary) _ 

ppm 

Aquatic 

organisms ‡ 

ppm 

Very highly toxic 2000 >5000 >100 

Except for weed control, glyphosate and glufosinate are efficient 

against some plant pathogens. For instance, glufosinate inhibits infection of 

glufosinate-resistant creeping bentgrass (Agrostis palustris) with several 

plant pathogens (Liu et al., 1998). Also, HRCs can be especially useful for 

eradication of parasitic weeds (Joel et al. 1995). According Altman (1993, 

cited by Duke, 1999), more additional and profound investigations need to be 

done on secondary effects of these herbicides in order to fully determine their 

roles in integrated pest management. 

Taking into consideration all previous mentioned advantages of new 

technology, herbicide industry appears to be rapidly transforming from a 

50


chemically based to biotechnology oriented industry. The largest pesticide 

producers of the US and Europe have invested heavily in plant biotechnology 

and seed industry. Every year, since the first experimental releases in 1987, 

HRCs have accounted for nearly one-third of field tests conducted under 

USA authority. The biggest part of trials are conducted by companies experts 

who have created and applied new technologies. Successful creation of new 

HRCs will be economical method of expanding the market for products for 

which companies have already have sophisticated equipment and highly 

specialized staff. 

Possible risks and concern of GMOs 

As every new technology, also GMOs, beside positive, may have 

some potentially negative aspects, which are, fortunately, still in the domain 

of speculation. Controversies surrounding GMOs commonly focus on human 

and environmental safety, labelling and consumer choice, intellectual 

property rights, ethics, food security, poverty reduction and environment 

conservation. Some of them are real and the experts are aware for that. They 

take every measure to eliminate them on time. There is not any reason for 

concern. The following text will elaborate some of the potential risks and 

negative implication from HRC technology. 

One of the real risk in cultivation of HRCs is possibility for 

development of weed resistant mechanism to non-selective herbicides. 

Namely, application of unilateral strategy in weed control management and 

multiple glyphosate and gluphosinate application presents serious threat in 

the process for appearing of resistant weeds (Derksen et al., 1999). Weed 

resistance to glyphosate and gluphosinate, according some authors 

(Bradshow et al., 1997; Waters, 1991) is less probable, and will be rarer 

evolved to glyphosate and gluphosinate than to many other herbicides. The 

reason for this, according to these authors, is slow development of functional 

genes of resistance and the rich biodiversity in agroecosystem where these 

herbicides are applied. Nevertheless, glyphosate-resistant weeds have 

appeared, first in rigid ryegrass (Lolium rigidum Gaudin). in Australia 

(Powels et al., 1998; Pratley et al., 1999), then goosegrass (Eleusine indica L. 

Gaertn) in Malaysia, and subsequently, hairy fleabane (Conyza banariensis 

LO. Cronq.) and horseweed (Conyza canadensis L. Cronq.), in the USA 

(Heap, 2001). Resistance to glyphosate in Australian ecosystem is result of 

long-term application of this herbicide in no-till system. No-till system has 

poor diversity than conventional systems. Weed resistance to glyphosate in 

the USA is recorded in HR soybean because of continuous use in so-called 

minimal diversity system (Powels, 2003). It is clear that weed resistance to 

glyphosate in previous mentioned agroecosystems is due to poor diversity 

51

Z. Pacanoski 

and unilateral weed control management. More scientists who study this 

weed-resistant phenomenon, agree about possibility for escalation of this 

problem and they emphasize importance for designing appropriate system to 

prevent development of weed-resistance in HRC system. Increased diversity 

i.e., a wider range of rotational crops, diversity of herbicides used (herbicides 

with different mode of action, for example sulfentrazol + glyphosate in 

soybean) (Krausz et al., 2003), better cropping practices leading to more 

competitive crops, and use of nonherbicide weed control, can reduce the 

dependence on glyphosate and reduce the likelihood of resistance developing. 

Other risk for this system are “volunteer HR crops”. Long-term use of 

HRCs, particularly in crop rotation system only with HRCs, can be a serious 

problem. Namely, the volunteer plants of previous HR crop in the next HR 

crop can be problem, if the next HR crop is resistant to the same herbicide 

like the previous one. To avoid this real risk, it should be applied a preventive 

strategy such as presowing/preplanting soil cultivation and application of 

alternative soil herbicides. The herbicides choice should be done very careful, 

because of possibility of multiple and crossing herbicide resistance. The best 

way to prevent this undesirable appearance is application of herbicide with 

different mode of action than glyphosate and glufosinate. Appearance of 

volunteer HR plants is concerned particularly in harvest of transgenic rice 

and soybean, when some seeds can shed on the soil during this operation. 

Introduction of new technology impose the question for possible 

influence of HRCs to biodiversity. It can not give precise answer on this 

question, although numerous investigations with HRCs are made all over the 

world. Maybe we can answer this question indirectly, toward conventional 

crop production and its influence to biodiversity. 

The most important crop grown in Brazil is soybean, with 

approximately 13 million ha planted. The most important weeds associated 

with the crop belong to families Poaceae, Amaranthaceae, Cyperaceae, 

Euphorbiaceae and Asteraceae (Foloni and Christoffoleti, 1999) (cit. by 

Riches and Valverde, 2002). Agriculture intensification, adoption of nontillage 

systems, and overreliance on herbicides has resulted in the increased 

occurrence of hard to kill broad-leaf weeds, including those in the genera 

Cammelina, Euphorbia, Ipomoea, Borrerlia and Tridax (Merotto et al., 

1999). Additionally, wild poinsettia (Euphorbia heterophylla L.) and hairy 

beggarticks (Bidens pilosa L.) have evolved resistance to ALS inhibitors 

(Ponchio et al., 1997; Theisen et al., 1997; Vidal et al. 1997). In Argentina, 

pigweed (Amaranthus quitensis H.B.K.) evolved resistance to imazethapyr 

and chlorimuron in soybean (Christoffoleti et al.,1997, cited by Riches and 

Valverde, 2002). Non-tillage systems and unilateral ALS-herbicide 

application changed biodiversity in the soybean. 

52


According to the fact that weeds are an important component of 

agrobiodiversity, shifts in the composition of weed flora provoke change of 

biodiversity (Spahillari et al.,1999). The impact of HRCs to biodiversity will 

be the same. According to Forcella (1999), it could be anticipated that most 

HRCs are associated with nonresidual herbicides and the promotion of zerotillage, 

the seed bank density of weeds with protracted emergence periods or 

of those emerging late in the growing season is more likely to increase as 

compared with that of other species more easily controlled. 

Changes in the type and frequency of herbicide application in HRCs 

will provoke gradual removal on perennial and colonization of annual weeds 

(Sweet et al., 1999). For biodiversity conservation and avoiding undesirable 

effects, choice of complex measures of weed control (integral weed 

management) is needed, particularly regular and timely soil cultivation, crop 

rotation and application of herbicides with different mode of action. 

One of the potential questions is: can HRCs become invasive beyond 

the field boundary Numerous experts agree that HRCs can not survive out of 

the agroecosystem’s boundary. This thesis is corroborated with the fact that 

in the process in their selection with application of molecular biotechnology, 

and then in the process of domestication, HRCs became completely depended 

on human activities. For example, transgenic varieties of soybean and maize 

which are cultivated in South America, according to Colwell (1994), are 

weak competitors to plants species out of the arable land. 

However, the possibility for exchange of genetic material between 

related HRCs and wild ancestors, conventional crops and weeds, concern 

scientists most. This phenomenon is very possible in the centers of their 

origin. Geographic distance and pollination system are key factors in existing 

of probability for genes exchange. Soybean, the first and the most cultivated 

worldwide HRC, is exotic plant, whose wild progenitors originated from 

China, Russia, Japan, and Korea (Palmer et al., 1996). That means, if HR 

soybean is cultivated out of its origin centres there is not threat for gene 

exchange and, in the same time, for plant biodiversity. 

Existing and real risk is possibility of exchange of genetic material 

between transgenic and conventional crops. Particularly this problem is 

stressed for farms certified for so-called organic production. In order to avoid 

pollen transmission from transgenics crops to crops for organic, and also, for 

conventional production, space isolation is necessary. But, still there does not 

exist precise regulative, which will define minimum distance between 

trangenics and other crops. 

The most serious threat for new technology is possibility for gene 

exchange between related HRCs and weeds. Many different sources have 

been consulted and analyzed in order to estimate risk of appearance of 

hybrids between HRCs and weeds. According to scientific investigations of 

53

Z. Pacanoski 

Keeler et al. (1996) and Arriola (2000) based on numerous research activities 

in Europe and North America, it is clear that HR crops and related weedy 

plants can exchange genes through pollen transfer. The identification of 

spontaneous hybrid forms in a number of crop-weed complexes is well 

established, including between Sorghum halepense (L.) Pers. and Sorghum 

vulgare Pers., and between wild and cultivated forms of Helianthus annus 

L.and Oriza sativa L. (Arias and Reisberg, 1994; Arriola and Ellstrand, 

1996). According to Dale (1994), possibility for gene exchange between 

HRCs and weed population depends of three factors: 

i) sexual compatibility between crop and weed 

ii) possibility of spontaneous exchange of genetic material 

iii) 

between crop and weed (spontaneous hybridization) 

the manner in which new characteristic in the crop-weed 

hybrid will behave under environmental conditions 

Formation of hybrids between HRCs and weeds will provoke 

difficulties in weed control, similar to those with herbicides resistant 

weeds in conventional crop production. The sexual transfer of genes 

from crops to weeds, as it was mentioned before, is probably the 

biggest risk for the environment and can limit the cultivation of 

transgenic species. It is case of weeds related to transgenic canola 

which transfers her pollen towards wild species of Brassica, Sinapis 

etc. To avoid this phenomenon, today a specific management is 

practiced, which involve: 

i) maternal inheritance 

ii) male sterility 

iii) seed sterility 

iv) cleistogamy 

v) apomixis 

vi) incompatible genomes 

If maternal inheritances are presented, the interest gene is expressed 

only in chloroplasts and can not be dispersed through pollen to nontransgenic 

plants. Male sterility (sterility of pollen) is very important to 

eliminate the crossings in the environment (outcrossing). Therefore, 

transgenic plants should be created by getting seeds where the interest gene 

should be dominated in the mother plants, and pollination should be done 

with a non-transgenic line. 

At cleistogamic plants pollination is made inside the flowers before 

these open. In this way the external crossing can be avoided (the case of 

Triticum durum). 

Apomixis is an asexual type of reproduction in which the plant 

embryos grow from egg cells without being fertilized by pollen—the male 

54


part of the plant. The result is production of seed which inherited only 

maternal genes, and the plants are identical with maternal plant. 

Conclusions 

Taking into consideration all advantages, disadvantages and risks 

which are connected with the new technology, particularly with HRCs, 

undoubtly one question is posed: how and to what extent is possible use 

HRCs without causing undesirable effects In order to be controlled, the new 

technology should be regulated by low. That means preparation and 

verification of international GMOs regulations and norms, possibilities of the 

pesticide-biotechnology industry to protect and recoup their investments 

Several countries have already established legislation on the release 

of HRCs which are product of the new technology. The EU states in the 

recently revised Directive 2001/18/EEC states that GMOs have to undergo a 

scientific assessment of risks to human health and environment. The 

Directive presents a framework for the risk assessment, which appears to be 

derived from the framework put forward by the joint consultation on food 

safety brought up by the World Health Organization (WHO) and Food and 

Agriculture Organization (FAO). 

It is clear, that HRCs are (or soon will be) strongly impacting weed 

management choice. Their mass use will decrease the cost of effective weed 

management in the short or medium term. Their use will speed up adoption 

of reduced and no-tillage agriculture, greatly reducing the environmental 

damage by farming by reducing soil erosion (wind and water) and by 

reducing the use of herbicides likely to be found in surface and ground water. 

Herbicides resistance and new weed species that arise as a result of this 

technology will be dealt with traditional methods, such as rotating and 

mixing herbicides and rotating crops. 

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241-246 

57


PRODUCTION OF ALLERGENIC POLLEN BY RAGWEED (AMBROSIA 

ARTEMISIIFOLIA L.) IS INCREASED IN CO 2 -ENRICHED 

ATMOSPHERES 

Taib Šarić 1 , Ivica ðalović 2 

1 Faculty of Agriculture, Sarajevo, Bosnia&Herzegovina, e–mail: tsaric@bih.net.ba 

2 Faculty of Agriculture, Čačak, Serbia&Montenegro 

Abstract 

Ragweed (Ambrosia artemisiifola L.) is tipically a pioneer plant, 

which invades recently disturbed soils. It belongs to the group of the annual 

plants that emit pollen during late summer and early fall near the end of the 

growing season. This pollen is produced in such large quantities that is a key 

contributor to ex-Yugoslavia hay–fever problems near the end of summer. 

Anemophilous pollen grains are airborne and meteorological factors 

have great impact on their dispersal. Precipitation, wind speed, temperature 

and air moisture are often cited as influencing airborne pollen concentrations 

(Emberin et al., 1996). Numerous studies have already dealt with these 

aspects. Recently, Bartkova et al. (2003) showed that temperature has a 

marked impact on ragweed pollen production in Bratislava, Slovakia. 

Relative humidity is an important factor as well but not quite as determining. 

In the same direction, Barnes et al. (2001) noticed that usual weather 

conditions, temperature and relative humidity have onl little influence on the 

day–to–day variation of ragweed pollen counts. However, unstable 

atmospheric conditions such as the crossing of a cold front has the greatest 

impact of all the weather–related events on airborne ragweed pollen counts. 

According to the authors, only heavy rainfall has a distinct impact on pollen 

concentrations. Peak pollen production has been described to occur shortly 

after sunrise and may be related to photo cycle periods or cooler morning 

temperatures and lower humidity. Different statistically based types of 

models trend to predict pollen concentrations from meteorological conditions 

as reported by Laiidi et al. (2003). Bringfelt (1982) subsequently published 

some correlation studies dealing with pollen concentrations and weather 

parameters for forecasting purposes. One of his main conclusions is that daily 

temperature values from early spring have a major influence on the timing of 

the beginning of the pollen season and subsequently on its day–to–day 

variation. 

Keywords: ragweed, aeroallergens, allergy, pollen, CO 2, climate change

T. Šarić and I. ðalović 

Introduction 

Recent studies have shown a link between warming trends within the 

past 50 years and the phenology and abundance of allergenic pollen released 

by a number of European tree species (Jaeger et al., 1996; Emberlin et al., 

1997). However, only limited data are currently available to evaluate the 

direct effects of rising atmospheric CO 2 concentrations on pollen production 

by allergenic plants and its potential impact on public health (Ziska and 

Caulfield, 2000). 

Human allergic responses to the pollen of certain plant species (hay 

fever and allergenic rhinitis) is a serious environmental health issue (National 

Institute of Health, 1993). Aeroallergens, including pollen, also play a role in 

the exacerbation of asthma (D'Amato et al., 1994). The prevalence of both 

hay fever and asthma has increased significantly in recent decades (Wuthrich, 

1991; Arrighi, 1995). Little research has been devoted to understanding how 

various components of global environmental change influence allergenic 

pollen production and, thus, the potential for pollen-related disease. 

An increase in the concentration of atmospheric CO 2 is one of the 

most certain predictions of climate change models. CO 2 concentration has 

increased by 29% since preindustrial times, and is expected to double again 

sometime between 2050 and 2100 (Houghton, 1996). 

Plants grown in CO 2 -enriched atmospheres generally grow faster and 

are larger at maturity, although the magnitudes of growth and physiological 

enhancements vary considerably with environmental conditions and species 

identity (Bazzaz, 1990; Curtis and Wang, 1998). In one recent study, Ziska 

and Caulfield (2000) found that exposing ragweed plants to the higher CO 2 

concentrations predicted in the year 2100 doubled the quantity of pollen 

produced. 

Ragweed is a plant common to roadsides and disturbed habitats 

throughout most of the United States and Canada (Basset and Crompton, 

1975). It has male and female flowers born on distinct axillary branches, 

allowing for independent control of allocation to sexes (Payne, 1963). 

Throughout its distribution, ragweed pollen is one of the most abundant 

aeroallergens in late summer and fall, and it is one of the primary causes of 

seasonal pollen allergy in North America (Lewis et al., 1983). 

Consequently, ragweed pollen and specific allergens extracted from it 

have been used in many clinical studies, and the biochemistry and genetics of 

ragweed allergens and their impacts on the human immune systems are well 

understood (Griffith et al., 1991; Naclerio et al., 1997). 

This study investigates the direct impact of rising CO 2 concentrations 

on pollen production of ragweed. The results can be used to more accurately 

60

Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in ... 

evaluate the future risks of hay fever and respiratory disease exacerbated by 

allergenic pollen, and to develop strategies to mitigate them. 

Pollen 

Most pollen grains are smaller than 80 microns which is about the 

width of a human hair. Some pollens cause allergic reactions in some people. 

Pollen allergies are specific to the individual and the pollen type. Pollen 

grains that are wind-dispersed cause most of the allergy problems because 

these are the pollens that make their way into our nasal passages and eyes. 

Pollens from some plants, such as roses and tulips, are too big to be 

transported by the air alone. They depend on insects and birds to carry the 

pollen from plant to plant. 

Most pollens are spherical in shape. Ragweed pollens, which bothers 

many people, appear to have spikes or other similar features. 

While grass pollen is most prominent in May and continues into 

September, most weed pollen quantities increase throughout May and into 

June, ragweed pollen is very significant from late August through mid- 

September. The first hard frost of autumn typically brings our pollen season 

to a close in October. Pollen seasons can last for several months. 

On average, grasses are the most potent pollen grain on human 

allergies. To put this in perspective, here is an example. If the air had a 

pollen density of 90 grains/m 3 for trees, it would take a density of only 20 

grains/m 3 for grasses to cause the same level of symptoms associated with 

allergies. It would take 50 grains/m 3 for weeds. On a grain for grain basis, 

grass pollen has a higher allergic potential than either tree or weed pollen. 

Because of these differences in allergic potential, it takes a higher density of 

weed or tree pollen to constitute a "high" pollen rating than it takes for grass 

pollen. 

Some studies have examined trends in pollen amount over the latter 

decades of the 1900s and found increases to be associated with local rises in 

temperature (Corden and Millington, 2001; Spieksma et al., 1995). Changes 

in climate appear to have altered the temporal and spatial distribution of 

pollen. For example, some studies have found that trends toward earlier 

pollen seasons are associated with local warming over the latter decades of 

the 1900s (Emberlin et al., 2003; Fitter and Fitter 2002), and recent reports 

have concluded that the duration of the pollen season is extended in some 

species (Huynen and Menne 2003). Finally, several studies have examined 

other attributes of allergenic plants, which have also been responsive to CO 2 

concentration and/or temperature increases (e.g. Menzel 2000; Wulff and 

Alexander, 1985). These latter studies provide indirect evidence of impacts of 

climate change on pollen aeroallergens. 

61


Impacts of climate change on aeroallergens: past and future 

A number of studies have revealed potential impacts of climate 

change on aeroallergens that may have enormous clinical and public health 

significance. 

Human activities have resulted in increases in the concentrations of 

atmospheric greenhouse gases and changes in global climate. Before the 

Industrial Era (circa 1750) atmospheric carbon dioxide (CO 2 ) concentration 

was 280±10 ppm for several thousand years (Prentice et al., 2001). It has 

risen since then to 373 ppm (Keeling and Whorf, 2004). 

It is estimated that global average surface temperature changed 

increased by 0.6 0 C since the late 19th century. Projected CO 2 concentration 

by 2100 ranged from 541 to 970 ppm (approximately 1.9 and 3.5 times the 

pre-industrial concentration). Global average surface temperature is projected 

to rise over the period 1990–2100 under all scenarios, ranging from 1.4 0 C to 

5.8 0 C (Cubasch et al., 2001). 

Climate change is likely to have impacts on hayfever (allergic 

rhinitis) and asthma via its impacts on pollens and other aeroallergens. 

Atmospheric variables that may have impacts on these allergens 

include CO 2 concentration, temperature, rainfall, humidity, and wind speed 

and direction. With allergic diseases already being a significant public health 

issue in many countries, the potential for any adverse impact resulting from 

climate change is of serious concern. 

Pollen amount 

Impacts of climate change on aeroallergens 

A number of studies have found increases in pollen associated with 

increases in CO 2 concentration and/or temperature. Ziska and Caulfield 

(2000) found pollen production of common ragweed increased significantly 

both from pre-industrial to current and current to the future CO 2 

concentration. Similarly, Wayne et al. (2002) found a significant increase in 

ragweed pollen production under an approximate doubling of the 

atmospheric CO 2 concentration, although the increase was smaller than that 

found previously by Ziska and Caulfield (2000), who had examined a smaller 

increase in CO 2 concentration from current to future. 

The impact of climate change on pollen production of common 

ragweed (Ambrosia artemisiifolia) has been assessed by Ziska et al. (2003), 

who used an existing CO 2 /temperature gradient between rural and urban 

areas. The higher CO 2 concentration and air temperature of the urban area 

resulted in ragweed that produced significantly greater pollen than that at the 

rural areas. Ragweed also flowered earlier in urban than in the rural areas. 

62


Significantly stronger allergenicity was found in the pollen from 

plants grown at the higher temperature. 

Plant and pollen distribution 

The potential for changes in the distribution of allergen producing 

species has been recognized since the early days of climate change and 

human health work (Last and Guidotti, 1991). It has been suggested that 

areas of perennial ragweeds are likely to extend, and northern colonies of 

annual ragweed, such as that in the UK, will probably become more 

persistent (Emberlin, 1994). 

There is some evidence that vegetational response to abrupt climate 

change, such as that expected over the coming decades, may be rapid (Peteet, 

2000). Weber and Mother (2002) recently suggested that one of the 

implications of increased pollen production associated with increased CO 2 

concentration could be more efficient wind pollination and, ultimately, 

greater propagation of the plant species. 

Research challenges 

The research done to date is of concern for at least two reasons. First, 

it suggests that the future aeroallergen characteristics of our environment may 

change considerably as a result of climate change, with the potential for more 

pollen (and mould spores), more allergenic pollen, an earlier start to the 

pollen (and mould spore) season, and changes in pollen distribution. Second, 

it demonstrates climate change has probably already had impacts on 

aeroallergens. However, further work is required. Study of the impacts of 

climate change on aeroallergens and related diseases presents many 

challenges. Some of these challenges, along with suggestions for further 

work, are outlined in this section. 

Land-use changes will be a significant factor in determining future 

aeroallergen, particularly pollen characteristics. For example, Emberlin 

(1994) has suggested that decreases in grassland and cereals in Europe would 

lead to decreases in grass pollen, and that the projected increase in oil crops 

such as oil seed rape (Brassica species) may lead to a greater aeroallergen 

load. 

Although further work is required in this area, with the evidence to 

date, it would seem prudent to consider alternative adaptive strategies. One 

adaptive strategy would be tighter management of a number of the allergenic 

plant species discussed in this article. For example, government authorities 

could consider more carefully which plant species are used in populated 

areas. It is important that public health authorities and allergy practitioners be 

63


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embrace the challenges that face further work in this area. 

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66


GENETICALLY MODIFIED HERBICIDE–TOLERANT CROPS 

– STATE AND PERSPECTIVES 

Goran Malidža 1 , Vaskrsija Janjić 2 , Ivica ðalović 3 

1 Institute of Field and Vegetable Crops – Novi Sad, Serbia and Montenegro 

2 Institute of Agricultural Research “Serbia” 

Centre for Pesticides and Environment Protection – Zemun, Serbia and Montenegro 

3 Faculty of Agronomy – Čačak, Serbia and Montenegro 

Abstract 

Development and production of genetically modified crops is the 

hallmark of the end of last and beginning of new century. The most 

remarkable commercial success regarding genetically modified crops has 

been achieved with herbicide – tolerant crops as HTCs offer the potential for 

many benefits: simpler weed control, more effective management of 

problematic and resistant weeds, control of parasitic weeds, use of minimum 

additional tool in integrated weed management, avoidance of yieldtillage, 

loss caused by current herbicides, etc. Potential risks associated with HTCs 

include: gene flow, herbicide resistant volunteers, selection of weed flora in 

favour of species less susceptible to herbicides, potential development of 

herbicide-resistant weeds, grower's increased dependency on herbicides, 

reduced application of integrated weed management, losing of traditional 

skills of weed possible decrease in biodiversity in fields, etc.management, 

Key words: genetically modified plants, herbicides, tolerance, weeds, resistance, gene flow, 

integrated weed control. 

Introduction 

A significant increase in crop production over the recent decades has 

resulted from growing highly improved cultivars, i.e. their grown hybrids as 

well as from modern agrotechnical practices. 

The latest achievements in molecular genetics, biochemistry and 

physiology largely contributed to breeding crops of improved qualites, of 

which the tolerance of herbicides seems the most intriguing. Therefore, the 

first generation of the genetically modified crops relate to crop inputs or 

agronomical properties. Genetically modified herbicide–tolerant crops have 

aroused an interest of numerous stakeholders, unanimously sharing an 

opinion that farmers, herbicide and plant seed producers benefit from such 

crops most, with end–consumers benefiting none (McHugen., 2000; James, 

2001).

G. Malidža et al. 

Over breeding the herbicide–tolerant crops, the methods of 

recombinant DNA (genetic engineering) may be used to obtain genetically 

modified, transgenic crops. Biotechnological boom also allowed new 

organisms to be bred, their isolation mode to come into being as well as some 

of the DNA fragments to be transeferred, and prokaryotic and eukaryotic 

genes to be combined, too. Therefore, an ever-lasting dream of geneticists to 

combine various pedigree genes when breeding organisms with either 

modified or by introducing entirely new traits or entirely new organisms 

came into being. (Bekavac et al., 2004). 

So far, the combat against weeds has been based on the indigenously 

herbicide-tolerant crops. However, so applied herbicides over several decades 

so far have led to numerous problems requiring new approaches to be made. 

The development of molecular genetics paved the way for genetic 

transforming of the individual plant species as well as for expanding genetic 

variability and breeding the herbicide– and other toxic compounds–tolerant 

crop genotypes. So handled, the genes have encouraged an entirely new 

herbicide application technology. The concept of genetic transformation or 

genetic engineering embraces all the DNA processes to be transferred from 

one organism to another as well as their expression in the host plant. Genetic 

transformation is considered to be the procedure allowing genes to be 

transformed between the species irrespective of their being cognate and their 

number of chromosomes (Hull et al., 2000). 

As a technique of foreign DNA transfer to the plant cell, genetic 

transformation requires the following: 

• identifying the gene to be transferred; 

• isolating and cloning the gene; 

• introducing the gene into the host genome; 

• replicating genetic material; 

• expressing genetic material; 

• transferring the cell morphogenetic ability, and 

• introducing structural genes so as to be inherited through generative 

reproduction with safety. 

Methodologically, genetic transformation may be attained by directly 

introduced structural genes into the host crop genome or through vectors. The 

vectors appearing over the gene transfer may be Agrobacterium plasmides, 

DNA of the crop viruses, DNA of the plant organisms, DNA of pollen as 

well as that of pollen tube. When breeding herbicide-tolerant crops, the 

methods of DNA recombinants (genetic engineering) may be attempted, with 

virtually genetically modified i.e. transgenic crops. In addition, crop 

tolerance towards herbicides may be exerted using somaclonal variabilities, 

mutations and commonly used modes in plant breeding (Dyer, 1996., cit. By 

Malidza et al., 2005). 

68

Genetically modified herbicide-tolerant crops – state and perspectives 

Over herbicide–resistant crop growing, the three principles have been 

taken into account, as follows: 

• introducing the genes responsible for hyper-reproduction of the 

enzyme affected by herbicide; 

• altering susceptibility of the crucial locus exposed to herbicide impact 

and; 

• introducing the gene responsible for detoxifying herbicides existing in 

the crops. 

The largest number of herbicide – resistant crops could be got altering 

the main locus exposed to a herbicide, using induced mutations in crops and 

microorganisms and introducing microorganism genes to synthesize enzymes 

responsible for detoxifying herbicides. 

An increasing growth of transgenic herbicide–resistant crops has 

largely contributed to weed control in recent years, with an array of merits 

favouring producers rather than conventional modes do. 

Current issues relating to this field, the significance of the genetically 

modified herbicide–resistant crops, their most important traits, a detailed 

account on the relevant accomplishments made worldwide so far as well as 

possible undesirable effects of the technology considered will be discussed in 

the paper. 

Genetically modified and herbicide–tolerant crops as a global challenge 

Herbicide–tolerant crops do not seem to be a new phenomenon, their 

acceptable level resistance being a fundamental precondition of using 

herbicides with safety. In addition, a new herbicide is approached by testing 

its selectivity compared to that in the leading grown plant species. However, 

due to other requirements to be met (toxicological, ecotoxicological, impact– 

range, prices etc.) developing new herbicides has been visibly slackened and 

become rather costly in recent years. Moreover, grown crops have had their 

tolerance altered due to a booming biotechnology, with tremendously 

increasing number of herbicide producers making a huge profit. With 

herbicide – tolerant crops, lower losses in yield, lower pesticide and 

production costs are expected, too. Booming growth of the genetically 

modified herbicide – tolerant and insect-resistant crops has upgraded the 

conventional crop management since the last decade of the last and the first 

one of current century, their canopy highly expanding (Tab.1). 

Tab. 1. Global area of transgenic crops from 1996 to 2003 (James, 2003) 

Year 1996 1997 1998 1999 2000 2001 2002 2003 

Million 

1.7 11.0 27.8 39.9 44.2 52.6 58.7 67.7 

hectares 

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As can be seen from Table 1., the total areas under the genetically 

modified crops increased by 40 times more from 1996–2003 than those in 

previous years. (James, 2003). Thus, in 2003, 73% accounted for total areas 

under transgenic crops, of which soybean, canola, maize and cotton did most 

(Tab.2). 

Table 2. Global area of transgenic herbicide-tolerant crops from 1999 to 2003 

(James, 1999, 2000, 2001, 2002, 2003) 

Crop 

Million hectares 

1999 2000 2001 2002 2003 

Herbicide tolerant soybean 21,6 25,8 33,3 36,5 41,4 

Herbicide–tolerant canola 3,5 2,8 2,7 3 3,6 

Herbicide–tolerant maize 1,5 2,1 2,1 2,5 3,2 

Bt /Herbicide–tolerant maize 2,1 1,4 1,8 2,2 3,2 

Herbicide–tolerant cotton 1,6 2,1 2,5 2,2 1,5 

Bt /Herbicide–tolerant cotton 0,8 1,7 2,4 2,2 2,6 

*Bt –insect resistance 

From the short – term point of view, not believing in no risks of 

transgenic crops, the world public seem suspicious and reluctant to put them 

into practice. For example, the North and South America countries rank best 

by genetically modified produces, the EU countries still lingering about 

whether or not to back up such produces. Nonetheless, in Europe, such crops 

have been estimated to be notably advantageous. Thus, Phipps and Park 

(2002) estimated that in case of growing genetically modified maize, 

soybean, canola and cotton resistant to insects, the annual pesticide 

consumption in the European Union countries would be reduced by 4.4 

million kg, with areas to be treated expected to be reduced by 7.5 million 

hectares, which would save roughly 20.5 million litres of petroleum and 

reduce carbon – dioxide emission in the atmosphere roughly by 73000 

tonnes. 

Breeding modes for herbicide–tolerant genotypes 

Different biotechnological modes applied to a larger number of crops 

gave rise to a notably higher crop resistance to herbicides (Tab.3). As the 

most reliable way in breeding herbicide–tolerant genotypes is reckoned 

selecting from the existing germplasm. A differing tolerance level to the 

herbicides was revealed in wheat (Snape et al., 1991) soybean (Fedtke, 1991) 

and some of the oriental grasses (Catanzaro, et al., 1993). As regards the 

resistance to herbicides, genetic variability may be attempted, recurrent 

70


selection intensified along with conventional crossing modes to obtain new 

cultivars, i.e. hybrids. However, this approach has not been widely accepted 

by breeders, primarily due to too poor crop genetic variability to withstand 

herbicides. 

Tab. 3. Methods of obtaining plants resistant to herbicides 

(modified according to Duke, 1996) 

Plant species Herbicides Methods 

Maize 

Glufosinate 

Imidazolinone 

Ciklosydim 

PB 

C 

C 

Wheat Glufosynate PB 

Soybean 

Glyphosat 

AT 

Sulphonilurea 

Sugar beat 

Glufosinate 

Sulphonilurea 

AT 

AT 

Barley Glufosinate PB 

Tobacco 

Glufosinate 

Glyfosate 

Sulphonilurea 

2,4–D 

AT 

AT 

AT 

AT 

Legend 

AT–Transfer og agenes by Agrobacterium tumefaciens 

PB–Genetic Gun 

C–Tissue culture 

S–Plant or seed selection 

As a usual method for obtaining herbicide–tolerant crops is assumed 

using mutagenous chemicals and X–rays used so far for seed treatment and 

mutation inducement, thereby helping separate soybean genotypes resistant 

to sulphonilurea herbicides. Tissue culture is highly significant to the 

herbicide–resistant genotype breeding. In this sense, growing plant cells in its 

tissue culture may exert a range of changes in its genetic composition, 

including those in gene distribution, fertility level as well as those in 

chromosome arrangement. Such a process, called self-cloning variability has 

become an important source of variability, which might have been effectively 

used in breeding (Scoweroft and Larkin, 1988). Despite a somewhat success 

made in this view at first, a larger number of mutants manifested a range of 

undesirable effects due to their low ability in this view. In this sense, an 

example of tobacco cell culture selection on glyphosate resistance is often 

mentioned. However stable regenerant resistance to glyphosate may be, the 

crops regenerized could not be used due to partial sterility and undesirable 

agro–economical properties (Dyer et al. 1988). On the other hand, an 

71


example in favour of the mode considered may be exposing maize 

embriogene callus culture to Imidazolinon, with some of its resistant portions 

being isolated from maize culture (Anderson and Georgheson, 1989). 

Additionally, several herbicide–resistant lines possessing one of the two 

partially separated dominant alleles responsible for differing resistance level 

were regenerized (Newhouse et al. 1991). The mode of recurrent crossings 

helped breed the lines with preferable agronomical traits, resulting in 14 

hybrids resistant to Imidazolinon (Duke, 1996). 

Also, as a mode of breeding herbicide–tolerant crops, hybridization 

favours those plant species, which may be crossed with weed species or wild 

allies possessing genes resistant to a particular herbicide. Crossing the weed 

species Brassica campestris resistant to atrazin with several grown species 

from the family Brassica has launched a few commercially significant 

genotypes resistant to atrazin, too (Beverski et al., 1980). Despite their yield 

being reduced by roughly 20% due to undesirable chloroplast mutation, such 

genotypes have been observed to inhabit extremely weeded areas where the 

conventionally grown varieties would not be yielding economically enough. 

Direct gene transfer claims an absolutely new approach to herbicide – 

resistant crop breeding. Numerous genotypes have been obtained from the 

directly introduced desirable foreign genes into the host plant genome. DNA 

hybridization (Southern blotting) (Sambrook et al., 1987), using DNA 

polymerase chain reaction (PCR) (Mullis and Faloona, 1987) and enzymatic 

activity analysis are generally accepted methods for checking whether or not 

foreign genes have been built in in the host cell gene. Theoretically, the 

protoplasts and cells inherent to any plant species may be transformed, but 

the problem of how to regenerate transformants from the callus obtained 

from plant culture is being inevitably encountered. The modes of direct DNA 

transfer may be split up into four groups, as follows: 

• genetic transformation through Agrobacterium tumefaciens; 

• “Gene gun”; 

• stimulating endocytosis chemically; 

• electroporation, and 

• microinjection. 

Genetic transformation through Agrobacterium tumefaciens 

The bacteria inherent to the family Agrobacterium are gram negative 

soil bacillary microorganisms. Agrobacterium is closely related with 

representatives of Rhizobium family responsible for nitrogen fixing in the 

root nodular bacteria intrinsic to Agrobacterium tumefaciens, whereas 

Agrobacterium rhizogenes may bring about an uncontrollable adventitious 

root growth (Janjic, 1996). 

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DNA transferred from a large bacterium Ti plasmide, subsequently 

infecting the plant cell, is presumed a key bacterial activity. The DNA 

portion being transferred contains a gene responsible for phytohormone 

formation causing tumor tissue. The portion considered is mainly transferred 

safely to the host plant genome, so that transgenic plant breeding rests on 

such an intrinsically more natural transfer system. The gene responsible for 

tumor formation is replaced with a desirable gene and its corresponding 

vector formed. Gene transfer through Ti cloned carry–overs Agrobacterium 

tumefaciens is mostly used for breeding transgenic plants such as tobacco, 

petunia and a range of agronomically significant dicotiledons (Lindsey, 

1992). However, the gravest and economically significant drawback of 

Agrobacterium system is that it cannot help transform monocolitedon plants 

from the family Poaceae. Its numerous species include the most dangerous 

and resistant weeds (such as Agropyrum repens (L.), Beauv., Sorghum 

halepense (L.) Pers. and the like). The efficacy of gene management through 

Agrobacterium is also undeveloped in certain economically significant 

dicotiledonous plants such as fruit species, eg. peach and sweet cherry. 

Indeed, their tissues do not tolerate an infection caused by Agrobacterium or 

are likely to be oversensitive to the bacterial toxins, thereby discouraging 

effective genetic transformation. 

Gene gun 

Gene gun helps introduce sped up tungsten or gold particles 1 – 4 µm 

by size covered with DNA. Pollen seeds, cell suspension, callus tissues, 

endosperm, leaf, scion vegetation cones and the like may be the object of 

transformation. This mode has proven the most efficient for obtaining fertile, 

transgenic crops of maize, with a somewhat success made in the experiments 

with soybean, beans, rice etc. (Cao et al., 1992). Of some of the genetic gun 

designs, the commercially most often used one is Kikker's (1993) gun. 

Although this method ensures no stable integration of the DNA introduced 

into the plant genome, it has helped transform maize with success. 

Chemical stimulation of endocytosis 

Protoplast may be transformed by directly stimulated endocytosis. 

Under particular conditions (high pH, high content of Ca 2+ ), polyehylene 

glycol (PEG) and polyvinyl alcohol are likely to reliably exert genetic 

transformation frequency from 1 – 5 x 10 -6 . Even a higher degree of genetic 

transformation via endocytosis could be attained in cauliflower amounting to 

7.6 x 10 -4 (Tanaka et al., 1984). Methodologically, however complex 

endocytosis seems to be for implementing genetic transformation, it has 

proven a mere routine with rice, being attempted in a larger number of the 

laboratories and varieties (Shimamoto et al., 1989). 

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Electroporation 

Electroporation implies a procedure of exposing cell to electric field 

with temporary pores taking place on the plasmalemma through which 

macromolecules such as DNA enter the cell. 

Microinjection 

Microinjection is referred to as a macromolecule (DNA, RNA, protein, 

virus or organelle) being directly pushed into the plant cell. Carry–overs of 

genetic transformation are directly introduced into the cytoplasm or nucleus 

intrinsic to the cells being immobilized on a solid medium using glass pipette 

tip 0.5–0.1 µm by size. 

This method enables introducing macromolecules and chromosomes 

with high precision, with the amount of built – in genetic material controlled 

with high accuracy, too. The cell wall is not necessary to remove, being 

useful to the species with an undeveloped regenerating system from 

protoplast. 

The most economically significant genetically modified herbicide– 

tolerant crops 

Theoretically, crops tolerant to all the herbicides may be bred, but only 

the economically important plant species and herbicides with more suitable 

properties (glyphosate, glufosynate ammonium, sulfonylurea, imidazolinon 

cyclohexandion, bromoxinit and the like) deserve mention. To consider 

significance of hazards due to such a technology, every single case, i.e. a 

grown crop and herbicide itself, to which the crop may exhibit resistance, 

should be analyzed. 

Glyphosate–tolerant crops 

The first commercialised glyphosate–tolerant crops were obtained 

introducing the gene for modified enzyme 5–enolpiruvil–shicimat–3– 

phosphate synthetase (EPSPS) imparting the biosynthesis of aromatic amino 

acids and being the key locus exposed to this herbicide. The gene for EPSPS, 

of lower propensity to glyphosate was isolated from Agrobacterium sp., 

strain CP4, enabling tolerance of the majority of the economically significant 

plant species (Wells, 1995). The principle of glyphosate detoxification was 

brought to bear introducing it into the plant gene from the bacterium 

Achromobacter sp., strain LBAA in order to synthesize an enzyme for 

glyphosate oxidoreductase (GOX). This enzyme catalyzes the fissure of C – 

N bonds existing in glyphosate up to the metabolites with no herbicide 

activity felt (Wells, 1995; Padgette et al., 1996). Taken by areas, the 

glyphosate–resistant soybean (Roundup Ready Soybeans) is considered the 

74


world leading transgenic crop, commercially used first in 1996, estimated to 

have spread on 41.4 million hectares in 2003, accounting for 61% total areas 

under transgenic plants. During the first year of the commercially cultivated 

glyphosate–tolerant maize, roughly 380.000 hectares were estimated to be 

under glyphosate–tolerant maize in the USA (Talpan, 1998). Apart from 

soybean and maize, the glyphosate–tolerant cotton and canola are considered 

the most important crops, economically. The results of numerous 

experiments suggest applying glyphosate to crops of altered tolerance rather 

than using standard weed control chemical practices (Moll, 1997). 

Glufosinate–ammonium tolerant crops 

Glufosinate–ammonium is amino salt of amino acid of phosphinotricin 

obtained from tripeptid bialafos (L–phosphonotricil–L–alanyl–alanyn). Its 

mechanism of impact based on inhibiting the enzyme, intrinsic to glutamene 

synthetase, responsible for synthesis of glutamine acid (Leason et al., 1982), 

resulted in worsened protein synthesis and nitrogen metabolizm with raised 

ammonia concentration in the plant cell and, therefore, its raised 

phytotoxicity. Certain species of the family Streptomyces produce tripeptid 

bialafos as well as an enzyme protecting the host plant from detrimental 

effect of its own metabolite. 

Further, the so–called BAR gene, isolated from Streptomyces 

hygroscopicus, is responsible for the tolerance to bialafos, while the gene 

isolated from S. viridichromogenes encodes the synthesis of 

phosphonotricin–acetyl–transferasis (PAT gene) for detoxifying 

phosphinotricin. Both genes are encoding an enzyme for detoxifying 

glufosinate–ammonium through acetylization of amino group, the first 

metabolite N–acetyl–glyphosinate being found to have no herbicidal activity. 

Glufosinate–ammonium – tolerant crops have been attained using BAR or 

PAT genes (De Block et al., 1987, Donn et al., 1990 a, b). This is referred to 

as a breeding basis with an array of glufosinate–ammonium–tolerant crops, 

canola, maize, soybean and sugar beet being the major ones. 

Compared with standard herbicides in sugar beet, soybean and spring 

canola, glufosinate–ammonium provided better efficiency (Rasche et al., 

1995), Rasche and Gadsby, 1997). While studying weed control potential 

with glufosinate–ammonium –tolerant maize under inland conditions, 

glufosinate–ammonium was estimated to have achieved an effect being at 

least at the level of standard hebicide combinations if not better when 

controlling the dominant weeds (Malidza, 2003). 

75


Imidazolinon– and sulfonilurea–tolerant crops 

A larger number of crops is deemed intrinsically resistant to a range of 

acetolactate synthesis (ALS) inhibitors because their enzymatic system is 

able to metabolize these herbicides prior to seriously inhibiting the targeted 

enzyme. Obtaining the imidazolinon- and sulfonilurea–tolerant crops is 

considered feasible via standard selection modes, coupled with inducing 

mutations and direct gene transfer. Two modes were used to obtain 

imidazolinon-tolerant maize. First, pollen mutagenesis helped obtain maize 

hybrids (the so–called IT) with ALS enzyme being altered, which, as a 

characteristic, was controlled with one dominant gene (Greaves et al., 1993). 

Second, contrary to the first mode, the selection in tissue culture with no 

mutagenous substances used resulted in the highly imidazolinon–resistant 

maize (IR) as well as in the crossed sulfonylurea– and triazolopirimidin– 

resistant one (Siehl et al., 1996). IT maize hybrid tolerance in the field 

conditions was tested using imazetapir in four times higher amount than 

required for weed control, without noticing adverse effects on the yield 

(Shaner et al., 1996). IT and IR maize hybrids are commercially used with 

tendency to grow only IT maize for allowing new genotypes to be bred with 

ease. In addition, the difference in withstanding acetolactate synthesis 

between the sensitive and imazetapiron-tolerant IT maize hybrid was sevenfold, 

with that in IR maize hybrid estimated to be one thousand times higher. 

The crucial enzyme in IT maize hybrid showed no tolerance of 

chlorsulphuron and flumetsulam, whereas IR maize hybrid withstood their 

200 to 2200 times higher dose rates than the sensitive maize hybrid did (Siehl 

et al., 1996). Further, the mutagenesis of microspores allowed the 

imidazolinon–tolerant spring canola to be obtained, thereby, evolving a new 

epoch in weed control not only for this plant species but also for the weeds 

from the family Brassicaceae. Also, wheat seems to be highly economically 

significant, tolerance of which to imidazolinon was attained through seed 

mutagenesis (Shaner et al., 1996). Of the leading grown crops, imidazolinon– 

tolerant sunflower has also paved the way for improving weed control using a 

wide–range–impact herbicides after crop and weed emergence. A wild 

sunflower originating from the USA helped breed the imidazolinon–tolerant 

sunflower, having developed resistance after seven years of using imazetapir 

on end (Al–Khatib et al., 1998), possessing a key enzyme resistant several 

times higher to imidazolinon. The mode of inheritance was partial dominance 

(Miller and Al–Khatib, 2000; Jocic et al., 2001), the total tolerance being 

attainable only if both hybrid components were homozygous to this trait. 

Apart from being resistant to imazamox, sunflower could tolerate imazetapir 

and imazapir, but could not sulfonylurea herbicides (Malidya et al., 2000). 

Imazamox in the imidazolinon–resistant sunflower has proved to be efficient 

in controlling dominant annual broad–leafed and grassy weeds (Malidza et 

76


al., 2002, 2003). Mutant selection ensured a larger number of the 

sulfonylurea–tolerant plants (Sebastian et al., 1989; Dekker and Duke, 1995). 

The sulfonylurea–tolerant soybean (STS) only registered on the US 

market in 1992 has spread and been applied most widely as yet. The STS 

crops can simultaneously metabolize herbicide and have higher tolerance to 

acetolactat synthetase. The increased rates of chlorimuron–ethyl and 

thiphensuphuron–methyl can be used for weed control in STS soybean 

(Young, 1997). The active matter of these herbicides may also be applied to 

the conventional weed control system in the USA, but in lower rates due to 

lower selectivity. The merit of STS soybean is the higher herbicide dose rates 

are applied, the higher efficiency is achieved. Moreover, urea and 

imidazolinon are considered to have suitable ecotoxicological properties, the 

lower rates of which can be used over a longer period, but invariably 

effectively protecting from weeds. Limiting factors of using the 

imidazolinon- and sulfonylurea–tolerant crops are assumed resistant weed 

growth and rather a constrained crop transfer caused by certain herbicides. 

Weed resistance develops swiftly and even several years of applying 

herbicides are required. Thus, in Lactuca serriola, resistance was exerted 

after five (Mallory–Smith et al., 1990) and in Helianthus annuus after seven 

years of the unilaterally used herbicide inhibitor ALS–e (Al–Khatib et al., 

1998). 

Cycloxidim– and setoxidim tolerant maize 

The herbicides from aryloxiphenoxipropionate and cyclohexandion 

groups are being used to control annual and perennial narrow–leaved weeds 

in broad–leaved crops. The mode of herbicide impact is inhibiting acetil co– 

enzyme being carboxilasis in monocotiledonous plant species. Maize 

tolerance of setoxidim, cycloxidim and haloxifop was achieved by selecting 

mutants in tissue culture via altering sensitivity of the key locus exposed to a 

herbicide (Marshall et al., 1992; Somers, 1994). The mode of inheriting this 

trait is partial dominance (Parker et al., 1990). Maize hybrids resistant to 

setoxidim are being commercially used in the USA (Poast Protected Maize) 

and establishing those resistant to cycloxidim is on its way in Europe. The 

herbicides used in the cycloxidim–tolerant maize are paving the way for a 

more flexible and efficient controlling of Sorghum halepense from rhizome 

and grassy weeds in maize (Malidza, 2001). 

Bromoxinyl–tolerant cotton 

Cotton resistance to bromoxinyl was attained introducing the gene 

intrinsic to bacterium Klebsiella ozaenae, encoding synthesis of the enzyme 

bromoxinyl, of a specific nitrilasis, responsible for bromoxinyl detoxification 

(Stalker et al., 1988, 1994, cit. Dekker and Duke, 1995). The presence of this 

77


gene ensures a high crop resistance to bromoxinyl, withstanding even ten– 

fold higher herbicide rates than practiced ones. Importantly, this approach 

contributed significantly to broad – leafed weeds control in cotton due to a 

shortage of chemical measures and an onset of phototoxicity caused by the 

existing herbicides. 

The merits of growing genetically modified herbicide–tolerant crops 

The glyphosate– and glufosinate–tolerant crops seem the most 

promising thanks to a wide–range impact of such herbicides. Also, the crops 

resistant to other herbicides (imidazolinon, sulfonylurea, cyclosidim), the 

resistance of which was built in through conventional breeding modes are 

promising, too. In general, the genetically modified herbicide – tolerant crops 

(GMHT) have the following merits: a facilitated and an economically more 

suitable weed control; a more effective weed control due to weed 

uncontrollability with herbicides used within the conventionally produced 

grown crops; herbicide use with higher flexibility; suitability of using 

herbicides after emergence allowing for a critical period and weed 

detrimental level; additional potential of controlling weeds resistant to other 

herbicides and parasitic weeds; potential for achieving higher yields for 

increased grown plant tolerance to herbicides; lower hazards to the 

environment through putting the ecotoxicologically more favourable 

herbicide-tolerant crops into production, and potential of involving 

alternative production systems (no–till and the like). 

A facilitated and economically more suitable weed control 

One of the most emphasized reasons for increasing (Dewar et al., 

(2000) areas under the individual genetically modified herbicide–tolerant 

(GMHT) crops is considered a facilitated weed control along with its lower 

cost rather than being with alternative weed control measures. Using one 

wide–impact-range herbicide on GMHT crops allows controllability over a 

large number of weeds without adding any herbicide to extend the existing 

impact-range. In most cases, the application of solely one herbicide in 

soybean, maize and sugar beet gives if not better, then at least equal effect to 

that with combined herbicides in the conventional production. Thus, in the 

conventional production system of sugar beet, several herbicides are 

combined reiteratedly, while the GMHT sugar beet receives an equal or even 

a better effect of glyphosate or glufosinate-ammonium. In addition to being 

facilitated, weed control costs have also been cut down as well as those 

relating to glyphosate with soybean, maize and sugar beet, being lower than a 

much more expensive alternative system of the chemically controlled weeds. 

78


Thus, as suggested by Dewar et al. (2000), the costs of weed control 

with sugar beet were estimated to be from 119 and 110 pounds per hectare in 

Great Britain in 1998 and in 1999, those of glyphosate and gluphosinate– 

ammonium, used in maximal rates for weed control, from 30 to 60 pounds 

per hectare. Even though the GMHT seed expenses are higher, their 

introducing will, hopefully, enable economically more acceptable weed 

control in the future. Furthermore, areal expansion under the glyphosatetolerant 

soybean in the USA gave rise to much reduced costs of the 

herbicides to be used in the conventional weed control system (Carpenter et 

al., 2002). 

More effective weed control on account of its uncontrollability with 

the herbicides used within mainstream crop production 

Among crucial reasons for introducing GMHT crops lies an answer to 

the recent problems encountered in weed control, such as resistance of weeds 

to dominant herbicides and weeds, belonging to the same family as the grown 

crop does, on which the available herbicides have no or poorer effect than 

those efficient with GMHT crops. Therefore, introducing GMHT crops will 

be promising for controlling a range of perennial and other weeds similar to a 

grown crop, rather than lowly efficient existing selective herbicides used in 

the mainstream crop production. Dewar et al. (2000) pointed out the 

significance of the glyphosate-resistant sugar beet in which self-emerging 

potato will be effectively controlled and the number of nematodes in the 

succeeding crops reduced at lower costs. As suggested by May (2003), within 

a crop, it is easier to control Cirsium arvense as well as other weeds at lower 

costs. Also, Sorghum halepense, Asclepias syriaca and other problematic 

weeds with the glyphosate-tolerant soybean have been proven controllable 

with notable success in the USA (Culpepper et al.; 2000; Pline et al., 2000). 

Numerous examples substantiate an effective controllability of problematic 

weeds, such as those from the family Brassisaceae in canola (Merker et al, 

2004), followed by Xanthium strumarium in sunflower after emergence 

(Malidza et al., 2003), Cynodon dactylon in maize (Malidza and Bekavac, 

2001) etc. Evidently, weeds could be highly controllable in GMHT crops, 

which is illustrated best by the fields under the crops considered. 

Herbicide use with higher flexibility 

The higher GMHT crop tolerance of herbicides allows their delayed 

application since the crops exhibit tolerance to them in later phases of the 

grown crop development (glyphosate, setoxidim, cyclosidim, gluphosinate– 

ammonium). For example, glyphosate in glyphosate–resistant maize may be 

used last of all the available herbicides (Carpenter et al., 2002). As far as 

herbicide use timing and crop and weed growing phase are concerned, the 

79


flexibility of glyphosate and glufosinate–ammonium use in the GMHT sugar 

beet seems significantly advantageous rather than being with other herbicides 

in this crop (Dewar et al., 2000). 

Suitability of using herbicides after emergence allowing for a 

critical period and weed detrimental treshold 

Speaking about crop growing phase, herbicide application in GMHT 

plants is likely to be highly flexible, with herbicides applied after emergence 

only if meeting economical requirements. Such a lawfulness applies not only 

to the conventionally used herbicides, but also to the individual GMHT crops 

for potential herbicide use throughout later GMHT crop and weed growing 

phases (Hurle, 1998; Martin et al., 2001). 

Additional potential of controlling weeds resistant to other 

herbicides 

Dominant herbicides used in the leading grown plant species embrace 

the representatives of triazin, chloracetamid, carbamide, sulphonilurea, 

imidazolinon, aryloxiphenoxipropionate, cyclohexandion groups, with a huge 

number of the weed resistant biotypes evidenced so far (Heap, 2004). 

Considering that glyphosate and gluphosinate–ammonium were not used on 

considerable areas in the crop production in the past, they may additionally 

help control weed resistance to the remaining herbicides. The potential of 

controlling Helianthus annuus resistance to acelolactat synthetase may serve 

as an illustration. That soybean has developed its resistance to the herbicides 

dominating this weed is a well-known fact in several countries of the USA, 

glyphosate more efficiently controlling soybean than all the alternative 

herbicides do in the glyphosate–resistant soybean (Allen et al., 2001). 

The potential of achieving higher yields for increasing grown plant 

tolerance to herbicides 

Under stressful environmental conditions, herbicides cause no adverse 

effects in the GMHT crops unlike frequent ones relating to the 

conventionally produced crops (Burnside, 1996). With the imidazolinone and 

sulphonilurea herbicide groups resistant crops, the risk of extended adverse 

effects caused by more persistent herbicide representatives to the succeeding 

crops may be reduced over their setting (the imidazolinone-resistant canola, 

maize and sunflower as well as the sulphonilurea–resistant soybean and the 

like). 

The potential of parasitic weeds control 

The parasitic weeds from the family Orobanche and Striga occupy over 

100 million hectares in the African and Mediterranean countries, thereby 

80


largely constraining the production of a greater range of sensitive grown 

crops (Gresset, 2000). Introducing single HT crops and using glyphosate and 

acetolactat synthesis inhibitor can visibly reduce the adverse effects of the 

weeds considered (Gressel, 1996). More than 100 million farmers in Africa 

have been found to loose more than a half of the total maize production due 

to weeds from the family Striga (Berner et al., 1995). Growing the 

imidazolinone–resistant maize and seed treatment with imazapir confirmed 

the potential for controlling parasitic weeds Striga hermontica and S. asiatica 

and 3–4 times higher increase in yield (Abayo et al., 1998, Kanampiu et al., 

2003). In addition, introducing the imadadozilinone–resistant sunflower 

favoured the control of Orobanche cernua. The potential of concurrent 

controlling this parasitic weed and the dominant weeds in the imidazolinoneresistant 

sunflower was also substantiated (Malidza et al., 2003). 

Lower hazards to the environment by putting the ecotoxicologically 

more favourable herbicide-resistant crops into production 

Glyphosate, glufosinate–ammonim, imidazolinons, sulphoniluree and 

cyclohexandions are considered to have suitable ecotoxicological properties, 

which will, when coupled with the previously mentioned ones, contribute to 

lower hazards to the environment. As calculated by Wauchope et al. (2001), 

replacing atrazin and alachlor with glyphosate and glufosinate–ammonium 

when introducing the genetically modified maize toward these herbicides, is 

likely to reduce the risk to groundwaters contamination. Since as lower 

glyphosate and glufosinate–ammonium dose rates as possible were 

attempted, only one fifth up to one tenth of the alachlor and atrazin 

concentration was therefore leached into deeper soil layers. 

Potential of introducing alternative production system 

Tending to use as economically acceptable production system as 

possible, the farmers in North America have been massively adopting some 

of the GMHT crops, highlighting their suitability for improving no–till 

production system. Thus, the areas using no–till production system have been 

expanding in the USA since the glufosat–resistant soybean came into life. 

The glyphosate – tolerant soybean grown in no–till production mode allowed 

weed control in the crop per se, to be more effective, whereas prior to 

introducing glyphosate–tolerant soybean, glyphosate had been used before 

sowing and emergence for controlling the existing weeds. Within no–till 

production system, the glyphosate- and glufosinate–ammonium resistant 

maize did not exclude using other herbicides and the best results have been 

accomplished combining glyphosate and soil herbicides before sowing with 

herbicides used after emergence (Helwig et al., 2003). In addition to no–till 

system, the tendency of producing soybean with a higher number of crops per 

81


unit area is increasing. So cultivated glyphosate–resistant soybean requires a 

lower number of treatments with herbicides due to different conditions under 

which weeds grow (Norsworthy and Oliver, 2001; Reddy, 2003). Also, 

introducing some of the GMHT crops will allow herbicides to be used when 

cultivating combined crops tolerant of the same herbicide, such as cyclo– 

oxide–tolerant beans and maize. 

Potenatial hazards to the genetically modified herbicide-tolerant crops 

Despite numerous advantages of GMHT crops, encouraging their 

cultivation does not necessarily mean a complete absence but inevtiably 

present hazards. Increasing dependence of farmers on herbicides is becoming 

a serious concern which will either set other measures back or put them out 

of practice. Moreover, new mainstream of herbicides and other policies 

developed for weed control are expected to be legging behind and ignored. 

Importantly, the gravest anxiety related to GMHT crops is associated with 

gene transfer to wild allies as well as with resistant weeds growth. Therefore, 

due to genetic variability of crops and chemical variability of herbicides, we 

cannot generalize hazards. As in previous cases, each case (crop, herbicide, 

wild allies and the like) should be regarded per se in light of the potential 

hazards and within single cases taking the following into account: 

• Which advantage over production of every single crop affords an 

additional character of tolerance to a particular herbicide 

• What is the likelihood and which are the consequences of gene 

transfer responsible for weed and wild allies resistance 

• What is the likelihood and which are the consequences of selfemerging 

plants or weeds on the rudumentary habitats as the problem 

encountered in the agroecosystem 

As suggested by previous authors, gene source is unimportant for its 

tolerance to herbicide when assessing the hazards considered, i.e. whether 

tolerance resulted from mutations within a grown crop or from the gene 

coming from another organism. From the other stakeholders’ points of views, 

such as consumers and producers, neither gene source nor the herbicide – 

tolerant crop mode production is that relevant for such hazards for the time 

being. The transfer of genes responsible for tolerance of herbicides may 

enhance weeds viability and adaptability to farming and non-farming areas. 

In addition, weeds are likely to receive the characters intrinsic to 

invading species, which is however more relevant to the genes responsible 

for insect resistance or disease causals. 

82


Development of resistant weed biotypes as a result of GMHT 

grown areas expansion and of intensified use of lower herbicide number 

on larger areas 

Weed resistance to herbicides is a genetic phenomenon, being an 

example of weed expedited evolution and their intrinsic power to survive. 

The process had a long genesis before herbicide–tolerant genetically 

modified crops. Expanding GMHT canopies using several wide range– 

impact herbicides suggests a faster developing potential of the weed biotypes 

resistant to dominant herbicides. 286 resistant biotypes have been recorded in 

171 weed species in the world so far (Heap, 2004). An evidence about weed 

biotypes resistant to glyphosate in 6 weed species (Heap, 2004) may be 

threatening when considering a future crop ranking tolerance to this 

herbicide. Lolium rigidum and Eleusine indica developed tolerance to 

glyphosate prior to introducing GMHT crops (Powles et al., 1998). Thus, the 

first resistant biotype Conyza conadensis was registered in the USA after 

three years of glyphosate application in soybean (VanGessel, 2001). More 

resistant weed biotypes can be precluded or delayed using combined 

herbicides of different impact fashion (Diggle et al., 2003). The same authors 

suggest this strategy being more efficient than herbicide rotation of different 

exhibiting effect manner. More frequently occurring resistant weed biotypes 

over the recent years entail a serious threat to individual GMHT crops, 

suggesting their sustainability to be tended over a longer period of time, but 

solely as the part of an integrated weed control management (Knezevic and 

Cassman, 2003). 

Gene transfer from the GMHT to wild allies and weeds 

Weed resistance is mainly the onset of selection within a particular 

weed population in conditions of reiteratedly used herbicide, where gene 

transfer from a grown crop tolerant to a particular herbicide to plant allies is 

an additional possibility. Those who deny GMHT crops mainly stress that 

such a risk stems from the very centre of origin of grown crops in single 

cases. This instance of risk has appeared in maize in central America, but 

appears to be insignificant in other areas. Gene transfer is likely to occur only 

between the sexually congenial plant species. Keeler et al., (1996) listed only 

11 of 60 grown plant species worldwide not to possess any wild allies. Of 13 

leading grown plant species, 12 were proven to natuarlly hybridize with wild 

cognates (Ellstrand et al., 1999, cit. Wolfenbarger and Phifer, 2000). 

Cultivating GMHT crops can increase crossing potential with compatible 

species, thereby enhancing the adaptability of the latter to farming and nonfarming 

ecosystems. In general, most of the grown crops are regarded unable 

to remain viable unless helped by man, with their abilities to survive being 

however differing from species to species. Being as much adaptable to the 

83


ecosystems as the herbicide-unresistant crops are, the herbicide–resistant 

ones bear no advantages over the other crops in the absence of herbicides 

within an ecosystem (Thill, 1996). Further, as a result of gene transfer, a wild 

ally of a grown crop is likely to acquire the traits intrinsic to the invading 

species. The herbicide–tolerant grown crops do not possess more expressed 

traits of the invading species than their non–transgene forms and wild allies 

do. Accordingly, direct or indirect impact and control over invading species 

have been estimated to roughly 137 billion dollars solely in the USA per 

annum (Pimentel et al., 2000, cit. Wolfenbarger and Phifer, 2000). Since 

2003, the grown sunflower resistant to imidazolinonim has been cultivated in 

the USA. Transfer of the gene, responsible for tolerance of sunflower to 

imidazolinonim, to a wild ally was confirmed by Massinga et al., (2003). 

Wild sunflower (Helianthus annus) served as a gene donor for 

tolerance to imidazolinonim while breeding the grown sunflower, only the 

spontaneity of gene transfer in the opposite direction being currently stressed. 

Also, that gene for tolerance of wheat (Clearfield) to imidazolinonim may be 

transferred to the weed Aegilops cylindrica through hybridization in natural 

conditions was revealed by Snyder et al., 2000; Andesron et al., 2004. The 

resistance of Aegilops cylindrica in monoculture of the wheat resistant to 

imidazolinonim was found by Hanson et al., (2002) to develop in less than 10 

years without and in a much shorter time than that with wheat hybridization. 

Genetically modified and herbicide-tolerant crops as volunteers in 

succeeding crops 

This is often emotionally referred to as „super–weed“ by extreme 

opponents, emphasizing the risk this technology bears. That grown crops 

becoming weeds in the succeeding crops for being linked with each new 

herbicide introduced into plant production system, seems nothing of a new 

problem. The results obtained in controlling self–fertilized grown plants in 

the succeeding ones at the start of growing canola tolerant to glyphosate, 

glufosinate–ammonium and imidazolinone appeared to be encouraging. 

However, that the spring canola (Brassica napus), being simultaneously 

resistant to glyphosate, gluphosinate–ammonium and imidazolinone, had 

emerged by spontaneous crossing in Alberta (Canada) was substantiated by 

Hall et al. (2000). This is a good example depicting hazards due to an 

intermingled resistance toward several herbicides of the congenial foreign– 

fertilized crops that might be as problematic as self-fertile crops are in the 

ensuing crops. In this case, an integrated crop rotation and herbicide 

management along with combining herbicides and other measures for 

preventing further progress of such occurrences and adverse effects of self – 

fertile crops, B. napus, with multiple resistance to herbicides may be 

recommended. 

84


Increasing hazard of damaging untargeted plants using a wide– 

impact–range herbicide 

Increasingly cultivated GMHT crops have also increased hazards of the 

wrongly used herbicides to the crops, not being resistant to a particular 

herbicide, and those of the herbicide solution drift on the susceptible ones. 

Damages to crops due to wrongly applied herbicides (the application of 

herbicide to which crop is not resistant) will occur, but the reasons for this 

should not be sought in increasing areas under the genetically modified crops 

tolerant to herbicides. Herbicidal drift on untargeted plants appears to be 

constant, which, with optimizing water amount for herbicide use, may be 

minimized (Ellis et al., 2002). 

Potential influence on biodiversity 

GMHT crops are gravely threatening biodiversity. If largely grown, 

such crops may even change the existing biodiversity of the agroecosystems 

subjected to an intense and biased use of the individual cropping practices. 

Thus, the relationship between growing genetically modified sugar beet 

tolerant to glyphosate and the number of birds, the species Alauda arvensis, 

was studied in Great Britain. It is expected that further decline in the number 

of this species will depend on a better controllability of Chenopodium album 

in the GMHT sugar beet, the seed of which provides this species an important 

food source (Watkinson et al., 2000; Dewar et al., 2002, 2003). Of 13 million 

hectares, 98% accounted for the glyphosate–tolerant soybean grown in 

Argentina in 2003 (James, 2003), its immense growing, giving rise to a fall in 

glyphosate prices (3 dollars per litre of glyphosate) expanding its application 

to non-farming areas. Over– and recap use of glyphosate (even of up to 16 

l/ha/year) caused weeds to entirely disappear not only around the soybean 

field and in the soybean crop itself, but also in all the areas treated with 

glyphosate being temporarily unused for plant production. In 2000, more than 

100 million litres of glyphosate were applied accordingly in Argentina. 

Biodiversity is assumed to have largely been jeopardized by an excessively 

used glyphosate on the larger areas rather than by the genetically modified 

glyphosate–tolerant soybean (Leguaizamon, 2001). 

Changes in weed flora 

Having created their own systems in weed control, agricultural 

producers are using those measures which, in their opinions, render optimal 

results. Since weeds adapt to every production system, a good farming 

practice may well postpone their adverse effects and the would–be lost 

advantages of recent technologies. Unless GMHT crops are used as the part 

of integrated weed control system, an expected scenario will be an altered 

weed floral composition and growth of its resistant biotypes (Knezevic and 

85


Cassman, 2003). Being so, the best optimality will be ensured by co– 

presence of the GMHT crops, the herbicides, to which crops exhibit 

tolerance, other herbicides and weed control measures, too. Even though a 

wide–impact–range herbicides (glyphosate, gluphosinate-ammonium) are 

being applied to the individual, presently, commercialized GMHT crops 

worldwide, weed flora is being likely to change by encouraging the naturally 

more resistant weeds to such herbicides and by increasing weed sharing, too 

(VanGessel, 2001). When introducing individual crops, farmers risk resting, 

primarily, on the herbicides, so putting the mainstream weed control 

measures out of use. 

Prospects and future of the genetically modified crops in Europe 

The herbicide–tolerant genetically modified crops entail an additional 

option to farmers when controlling weeds, which would be appropriately 

used only if incorporated into integrated weed control management (Malidza 

et al., 2005). 

A rapidly increasing area stretch underneath the herbicide–tolerant 

genetically modified crops envisages changes to be on their way in Europe 

(Agrow, 2003). 

That genetically modified crops are advantageous is doubtless. 

However, their use should be approached with utmost care because little is 

known about possible implications and adverse effects such crops may imply. 

The use of transgenic crops for scientific purposes is allowable in the 

country, their further ranking hugely depending on the EU one. 

Table 4. Forecast of GMHT crops participation in European Union to 2013 

(Agrow, 2003) 

Crop 

First year of 

production 

% of area planted to 

a particular crop in 

2008 

% of area planted 

to a particular crop 

in 2013 

Maize 2005–2007 10 35–45 

Oilseed rape 2006–2008 0–5 20–30 

Soybean 2007–2009 0–10 30–40 

Sugar beet 2006–2008 5–10 40–50 

Wheat 2008–2011 0 15–25 

Rice 2007–2009 0–5 30–40 

Cotton 2006–2008 5–10 40–50 

86


The issues considered are being discussed at meetings such as Codex 

Alimentarius, OECD Seed Schemes, Convention on biological divergence- 

CBD, with regulations varying from country to country, from complete 

prohibition of GMHT crops, GMO in Algeria to their full liberalization in the 

USA and in Argentina and de facto moratorium in EU countries (Masirevic 

and Bugarski, 2004). In light of GMHT crops, the EU countries deserve 

special mention. The fact that 22,000 ha of maize, i.e. 2,000 ha BT maize had 

been sown in Spain and France in 1998, was pressurized by public opinion, 

opposing not only the GMHT crops introduction but also the new 

transformant experimentation after the initiative had been made by Denmark, 

Greece, France and Luxembourg, so bringing them to a standstill (Phipps and 

Park, 2002; Bekavac et al., 2004). 

However, the moratorium in the EU countries due to application of 

GMHT crops was even more tangled when the USA said it would lodge a 

complaint to the World Trade Association, accusing the EU of having based 

such a moratorium on the entirely unscientific principles, giving no good 

reasons for it any longer. Still, denying GMHT crops by EU seems to have 

eased up with more optimism shown recently. In 2002, the EU legalized 

banning the moratorium, some of its members still hanging on of whether or 

not to accept the GMHT crops and pondering their being tightly linked with 

numerous factors. 

Despite the existing scenarios for the GMHT crop technology 

adaptation approaches, GMHT crops are expected to share 10% total EU 

agricultural areas in the next 5 years, during which time, GMHT crops ought 

to be validated, enlisted, some of their traits–introduced into the 

commercially most important varieties and hybrids (Bekavac et al., 2004). 

Overall, in the next ten years, the GMHT crops are expected to share 

EU areas, but depending on production specificities from region to region 

(weeds and pests) as well as on those from crop to crop (BioPortfolio, 1997– 

2003). 

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Instruction to Authors in Herbologia 

One copy of manuscript in English should be submitted by e-mail or 

as a hard (paper) copy and a floppy disc. 

Manuscripts should be computer typed in MS Word, single spaced, 

on the page (paper) format of B5, font of Times New Roman, font size 12 

(keywords and list of references with font size 10). The text lines should be 

justified. The length of the paper can be up to eight pages. 

The paper should start with the title of the article, the names of each 

author, his/her institution, address and e-mail address. 

Abstract would not exceed 300 words or 20 lines. Keywords, up to 

two lines long, should be listed below the abstract. 

Main text includes intruduction, materials and methods, results and 

discussion. Footnotes should be avoided. SI units should be used. Reference 

list should be ordered alphabetically. Examples: AUTHOR, X.Y. & Z.Q. 

AUTHOR, 2001: Title of article, Journal title in Italics, 12, 78-84. Or: AUTHOR, A., B. 

AUTHOR, 1998: Book title (ed. GH Editor). Publisher, Place, Country. 

Figures and tables should be numbered consecutively and should have 

an appropriate caption or legend. 

Scientific names should be in italic. When a plant name is repeated, it 

can be abbreviated, e.g. C. album. For crop plants, common English names 

are used, but the scientific name can be given in parentheses at the first 

mention in the main text, e.g. oats (Avena sativa). Both British and American 

forms of common names can be used (e.g. corn and maize, alfalfa and 

lucerne etc.), up to the choice of the author. For herbicides and other 

chemicals, in Materials and methods, one should state common approved 

names and trade names, e.g. glyphosate (Roundup 360 a.i. L -1 , Monsanto), 

and thereafter only trade names. Dose of herbicides should be expressed in 

terms of active ingredient (e.g. a.i. ha -1 ).

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