HERBICIDES in Asian rice - IRRI books - International Rice ...

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ECONOMIC AND TECHNOLOGICAL INFLUENCES ON HERBICIDE USE IN THE LESS DEVELOPED COUNTRIES OF ASIA K. Moody Production and consumption of rice are closely associated with the nations of South, Southeast, and East Asia. In 1991, 520 million tons of rice were produced on 148 million hectares (IRRI 1993). Current production, however, cannot be sustained, much less increased to the level needed within the next 25 yr, without greatly increasing the productivity of current cropland (Barbier 1989). Improved weed control will be an essential component of the technology needed to achieve that objective (Williams 1992). Herbicides are currently the most widely used method to control weeds. This agrochemical can be expected to be a major growth area in the pesticide industry of less developed countries for at least the next decade. For example, the rice herbicide market in China and India could increase from a total of US$67 million to more than $550 million (Woodburn 1993). Over the next 6-8 yr, average global expenditure on rice herbicides could exceed US$10 ha -1 , compared with the current US$7.50 ha -1 . In the Philippines, sales of pesticides during the 5 yr 1985-89 grew an average 19.8% for herbicides, 13.8% for insecticides, and 2.9% for fungicides. Most of the herbicide (85%) was applied to rice, with more than 1 million ha treated nationwide (Cruz 1990). Herbicide use on rice increased from 54% of all herbicide sales in 1981 to 82% in 1987 (Rola and Pingali 1993). In India, herbicide use during the 1980s dramatically outstripped use of other pesticides. Herbicides were only 2% of total pesticide use in the 1970s; they now account for 12% of the herbicide market. About 2,000 t of herbicides are used annually on more than 4 million ha of rice (Mehta 1992). In the Punjab area alone, herbicide use in transplanted rice increased almost 600%, and 90% of the ricelands are now treated with herbicides (Brar and Randhawa 1992). Herbicide use also is increasing in less favorable rice-growing areas. In Thailand, the rice herbicide market has increased dramatically. Products such as bensulfuron-methyl, pretilachlor, and fenoxaprop-ethyl have benefited; older her-
icides such as 2,4-D and butachlor continue to be important as well (Woodburn 1993). In Malaysia, herbicide use in rice in the Muda irrigated area increased 700% in 9 yr, from 166 t in 1980 to 1,318 t in 1989 (Ho et al 1990). FORCES PRESSURING HERBICIDE USE The increasing use of rice herbicides can be attributed to the substitution of chemical weed control for manual weeding in irrigated rice and to a growing preference of farmers for direct seeding their rice instead of transplanting. Labor availability Manual weeding of rice has a high labor requirement. A major factor affecting rice culture and weed control technology in many countries is the steady movement of labor from rural to urban areas, as industrialization creates more attractive employment opportunities. Crop establishment practices As transplanting costs increase, farmers increasingly are switching to labor-saving direct seeding of their rice crops. Weeds become a more serious problem, and farmers adopt herbicides (Tan et al 1992). Erguiza et al (1990) reported that farmers who wetseeded their rice relied more heavily on herbicides to control weeds than did farmers who transplanted. Shifts in weed flora In Peninsular Malaysia, increased weed problems and the shift in weed flora that resulted from adoption of direct-seeded rice have boosted use of herbicides, and the type of herbicides used has changed. In transplanted rice, phenoxy herbicides were applied 10-14 d after transplanting to control broadleaf weeds and sedges. With direct seeding, grass weeds have become dominant, resulting in a shift to residual herbicides applied soon after sowing (Hamzah and Ramasamy 1993). Herbicides were introduced in Sabah, Malaysia, along with wet seeding. Molinate is used to control increased grass problems in wet-seeded rice in Kota Marudu. In Cho Moi District, An Giang Province, Vietnam, weed species shifted as crop establishment changed from transplanting to wet seeding. Sedges dominate in transplanted rice due to standing water in the field; in wet-seeded rice, grasses dominate. This has changed the herbicide used, from 2,4-D to pyrazosulfuron-ethyl. COST-BENEFIT OF HERBICIDE USE Herbicides are a highly productive input, with the marginal return for every dollar invested strongly positive. As a general rule, the higher the wage rate or the more 234 Moody
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DEDICATION To Keith Moody WEED SCIE
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The International Rice Research Ins
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Bioherbicides and weed management i
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ful insects caused adverse response
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The need to raise yields and mainta
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ACKNOWLEDGMENTS Any volume that dra
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Overview
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as more lucrative, full-time job op
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Table 3. Herbicide use in rice prod
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only 3.3:1. The benefit-cost ratio
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EFFECTS ON SOCIETY AND ECOSYSTEMS S
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mulate in soils and in water tables
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unds from the field into canals and
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tion. Even if herbicide mixtures ar
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plant pathogens for controlling gra
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spectrum herbicides glufosinate-amm
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De Datta SK. 1981. Principles and p
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Li KM, Li PZ. 1996. Effect of herbi
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Vongsaroj P. 1994. Weed control in
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i ce env ironments and how they res
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Soil fertility. Monochoria vaginali
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Such problems could be avoided by a
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Ho NK, Md Zuki I. 1988. Weed popula
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HERBICIDES IN UNITED STATES RICE PR
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LOSSES TO WEEDS IN U.S. RICE US. ri
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propanil, which remains the backbon
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4. U.S. rice yields and adoption of
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6. Use of herbicides to control bro
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8. Thiobencarb and molinate transpo
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oping programs that curtail negativ
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Dunshee CF, Jones JW. 1924. Results
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Impacts of herbicides
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Pesticide users The pesticide user
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Table 3. Frequency of pesticide app
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Poly- Multiple Eye Pulmonary neurop
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(weight/height) had the expected ne
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Table 5. Anticipated health costs o
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When no consideration is given to h
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MAFF. 1991. Pesticides approved und
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and analyzed. We used this data bas
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soluble herbicide is distributed in
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of the rice herbicides thiobencarb
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germination because they compete fo
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in N 2 fixation and nitrate reducti
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Table 3. Effects of pesticides on n
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transformations in soils are studie
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Floodwater invertebrates Applicatio
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tally prevented photosynthetic acti
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CITED REFERENCES Almazan LL, Robles
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Mandal BB, Bandyopadhyay P, Bandyop
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Smith RJ, Flinchum WT, Seaman DE. 1
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IMPACT OF HERBICIDE USE ON THE ENVI
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Factors that reduce toxic risk Phys
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Table 3. Persistence in soil of ric
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One infamous herbicide spill occurr
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investigated because of the large,
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Given the current state of knowledg
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Way JM, Newman JF, Moore NW, Knaggs
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powder)—one-third the total amoun
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tants, however—such as cyanide an
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In both 1987 and 1988, 42 t of copp
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compounds such as the germicide Aso
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otation of one wet season, one dry
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ECOLOGICAL FORCES INFLUENCING CROP-
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may also vary with the resource use
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crease competitive ability into cro
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Tilman D. 1988. Plant strategies an
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Table 1. Important rice weeds in te
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2. Costs of production of rice and
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covered only about 7,500 ha in 1993
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Table 5. Herbicide-treated area in
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Table 6. Dominant weed species in K
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cides in the mix. Most mixtures, wh
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Kim KU, Shin DH. 1993. Development
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INTEGRATED WEED MANAGEMENT IN RICE
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after crop establishment) mostly co
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Table 2. Most common rice herbicide
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Table 4. Examples of rice herbicide
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portant where direct method options
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too wet. Optimum moisture is needed
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For direct-seeded rice, the availab
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visible effects. These methods are
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CITED REFERENCES Ampong-Nyarko K, D
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Jikihara K, Kimura I. 1977. Benthio
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Watson AK. 1992. Current status of
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1. Framework for planning and imple
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Baseline data The problems associat
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3. Filling vacant areas in the fiel
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emained the dominant weed, their in
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6. Cultural practices in the Muda a
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LESSONS LEARNED FROM THE PROGRAM St
Page 196: Ho NK, Md Zuki I, Asna BO. 1990. Th
Page 199 and 200: Using mycoherbicides involves apply
Page 201 and 202: Community education also is importa
Page 203 and 204: the crop of interest. This should i
Page 205 and 206: asically biological, technological,
Page 207 and 208: cause they are likely to be applied
Page 209 and 210: Similarly, the risks of bioherbicid
Page 211 and 212: Baki MM, Azmi M. 1992. Integrated m
Page 213 and 214: Matthews GA, Bateman RP. 1990. Appl
Page 215 and 216: Watson AK. 1985. Host specificity o
Page 217 and 218: vars as it was with very short-dura
Page 219 and 220: While it may not be possible to ide
Page 221 and 222: CITED REFERENCES Ahmad S, Majid A,
Page 224 and 225: USING BIOTECHNOLOGY IN GENETIC IMPR
Page 226 and 227: Molecular markers are being used ro
Page 228 and 229: use of herbicides as part of a rice
Page 230 and 231: A final strategy would be to use bi
Page 232: Rathore KS, Chowdhury VK, Hodges TK
Page 235 and 236: Putnam and Duke (1974) postulated t
Page 237 and 238: Visual ratings were made 7 wk after
Page 239 and 240: nels; and most of the genotypes tha
Page 241 and 242: Leaf Root Leaf Root Leaf Root Leaf
Page 243 and 244: One hypothesis is that rice plants
Page 246: Use of herbicides in Asian rice
Page 251 and 252: lems, it has resulted in quantitati
Page 253 and 254: Reasons for herbicide selection Far
Page 255 and 256: Carey VP III, Talbert RE, Baltazar
Page 258 and 259: EXPERIENCE WITH RICE HERBICIDES IN
Page 260 and 261: 2. Time spent weeding Japanese rice
Page 262 and 263: 3. Area of Japanese ricefields rece
Page 264 and 265: 4. Sequence of herbicide applicatio
Page 266 and 267: Table 6. Important weed species in
Page 268 and 269: CURRENT PROBLEMS IN WEED MANAGEMENT
Page 270 and 271: DEVELOPING A WEED MANAGEMENT STRATE
Page 272 and 273: (Timmer et al 1983, World Bank 1993
Page 274 and 275: gets of plant growth regulators and
Page 276 and 277: in their role of implementing agric
Page 278 and 279: clearly needed if farmers are to av
Page 280 and 281: Kuhrt WJ. 1992. The California grap
Page 282 and 283: Participants Dr. Heidi Albers Food
Page 284 and 285: Dr. Gurdev S. Khush International R
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