Wheat Production Guides.pdf - Pannar Seed
PANNAR SEED (PTY) LTD
Production Guide Series
Wheat
TABLE OF CONTENTS
A) INTRODUCTION ............................................................................................................. 1
B) CULTIVAR INFORMATION – FIRST STEP TO SUCCESSFUL
WHEAT PRODUCTION .................................................................................................. 2
1. Introduction ......................................................................................................... 2
2. Plant Breeders’ Rights ........................................................................................ 2
3. Certified seed is the key to success ................................................................... 2
4. Cultivar selection ................................................................................................. 2
C) SOIL PREPARATION ................................................................................................... .8
1. Conventional tillage seedbed preparation ........................................................ .8
2. Conservation tillage seeding systems ............................................................... 9
D) YIELD PLANNING ......................................................................................................... 9
E) FERTILISING GUIDELINES FOR WHEAT PRODUCTION ....................................... 10
1. Soil acidity ...................................................................................................... 11
2. Nitrogen fertilisation ........................................................................................ 12
3. Phosphate fertilisation .................................................................................... 16
4. Potassium fertilisation .................................................................................... 18
5. Micro-elements ............................................................................................... 19
F) WATER QUALITY AND WEED HERBICIDES ........................................................... 20
1. Factors that affect the salt antagonism of herbicides .................................... 20
G) INSECT CONTROL ...................................................................................................... 21
1. Aphids ............................................................................................................. 22
2. Other insect pests ........................................................................................... 24
H) DISEASE CONTROL .................................................................................................. 26
1. The risk of fungal infection ............................................................................. 26
2. Chemical control of fungal diseases .............................................................. 26
3. Root diseases ................................................................................................. 28
4. Stem, leaf and spike diseases ....................................................................... 29
5. Smut ................................................................................................................ 33
I) GRADING AND QUALITY ............................................................................................ 34
J) BIBLIOGRAPHY ........................................................................................................... 35
A) INTRODUCTION
In South Africa, wheat is produced in both the summer and winter rainfall regions.
Approximately 50% of the total area planted to wheat locally is cultivated under
dryland conditions in the summer rainfall region. Although production under irrigation
in the summer rainfall region amounts to less than 15% of the total area cultivated
locally, as much as 30% of the total wheat harvest is produced under irrigation due to
the higher yield potential.
Dryland wheat production in South Africa is distinctive for its low average yield in
comparison with most of the major wheat producing countries. The stringent quality
requirements for newly released cultivars are often blamed for slower than expected
progress in yield increases of local breeding programmes. Other limiting factors such
as variable climate conditions (including dry, warm winters) and low soil fertility,
however also have an effect. Yield losses were also caused by the introduction of
new diseases such as yellow/stripe rust (Puccinia striiformis) in 1996 and the
subsequent emergence of new pathotypes, as well as the introduction of the Russian
wheat aphid in 1978 and the emergence of a new biotype in 2005. The indirect
consequence thereof was that breeding programmes discontinued many promising
germplasm lines with higher yield potentials due to susceptibility to new diseases such
as yellow/stripe rust or more virulent disease-causing organisms or pests. This
resulted in local breeding programmes making more progress in creating specific
resistance or quality characteristics as opposed to improving yield performance. Farm
saved seed as well as the illegal sale of wheat seed has reduced the profitability of
wheat breeding programmes and if these practices continue unabated the profitability
of future wheat production will be significantly reduced, as the development of new,
improved cultivars will lag behind.
Notwithstanding these considerations, the local wheat producer must be able to grow
wheat profitably and stand in direct competition with imported wheat. To increase
profits per area unit, producers continuously improve their planning and seek more
information regarding best management practices. This guide is aimed at helping the
producer make more informed decisions for profitable wheat production.
Figure 1: Botanical Diagram of Wheat Plant
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B) CULTIVAR INFORMATION – FIRST STEP TO SUCCESSFUL WHEAT
PRODUCTION
1. INTRODUCTION
Cultivar selection is one of the most important considerations in risk management and
maximising yields. Cultivars differ in characteristics such as area adaptability, yield
potential and stability, agronomic characteristics and in terms of tolerance to
diseases, pests and aluminium toxicity. Although there is no perfect cultivar, the
producer can put together a package to minimise or neutralise the riskiest aspects of
wheat production in the specific area or farm.
2. PLANT BREEDERS’ RIGHTS
The aim of this Act (Act No. 15 of 1976) is to protect companies that invest millions of
Rands in cultivar development and provide legal protection to cultivar breeders and
owners. The rights of the cultivar breeder or owner include that no party may multiply,
prepare for planting, sell, export or keep seed in stock without the necessary
authorisation or licence from the holders of the rights. Upon conviction, the guilty
party shall be liable to a fine or imprisonment. There are several examples of
successful persecutions under this law.
3. CERTIFIED SEED IS THE KEY TO SUCCESS
The primary objective of seed certification is the maintenance of genetic purity in
seed. All requirements and standards of certified seed production are prescribed by
seed laws and regulations. The ultimate objective is to create seed with high genetic
purity, which is binding for cultivars listed on “Table 8”. Cultivar authenticity and seed
quality is therefore guaranteed. This offers a buyer protection and peace of mind as
well as a system for the follow up of complaints and possible claims.
4. CULTIVAR SELECTION
The selection of a cultivar is principally an economic decision, where the producer
must find a balance between risk and yield potential. Cultivar selection should be
based on reliable long-term data and should be revised annually to make provision for
new, improved cultivars. This should ensure the highest average profit per production
unit in the long term. A summary of the important considerations in cultivar selection is
provided below. The PANNAR product catalogue provides a comprehensive
summary of the most up-to-date information available on the PANNAR range of wheat
cultivars. This information is based on perennial research results and is given in good
faith. Producers must be aware that the development of new rust pathotypes and new
Russian wheat aphid biotypes may influence cultivar reactions within a given season.
The product catalogue is updated annually to ensure that the most recent information
is available to producers.
Yield potential:
Wheat cultivars differ in terms of yield potential; certain cultivars only perform at low
yield potential levels, while others are only adapted for high yield potential levels.
Where spring rainfall is the yield-determining factor, the ideal cultivar is the one that
produces competitive results under both high and low yield potential levels. In
general, the long growing season cultivars are less suited to areas with a low yield
potential, either due to shallow soils or long-term climate conditions. The selection of
cultivars should therefore be based on the long-term yield potential of a specific land
area or farm where soil, climate and manageability should be the determining factors.
Plant disease and pests:
The prevalence of a specific disease or pest in the area should be the determining
factor here. In areas of high disease or pest prevalence, the producer should
consider a more tolerant or resistant cultivar. This affords the producer the opportunity
to manage input costs over the long term and reduce the risk of crop damage and the
associated yield losses that may result from poor timing of spray applications. The
ability of disease-causing organisms and pests to adapt and therefore to overcome
the resistance must also be kept in mind. Wheat cultivars classified as resistant must,
as with susceptible cultivars, be monitored for the occurrence of diseases or pests
and susceptible reactions on resistant cultivars should be reported to the owner of the
cultivar concerned.
Seed price:
The price of seed is often an important factor when producers exercise their choice of
cultivar(s). More important is the use of independent long-term yield and grading data
when considering whether a more costly wheat cultivar is worthwhile growing in the
particular area.
Agronomic traits:
Agronomic traits such as straw strength and standability are of the utmost importance.
The selection of an unsuitable cultivar or the application of incorrect management
practices may result in significant yield losses. Under irrigation, chemical agents
which work against lodging are used with success on cultivars with a high yield
potential and an inclination to lodge.
An important factor in cultivar selection is aluminium tolerance, especially where the
topsoils and/or sub-soils reach AI 3+ levels that are toxic to sensitive cultivars.
PANNAR offers a range of wheat cultivars for dryland cultivation with strong
aluminium tolerance. This offers producers a short-term solution when lime cannot be
administered on time.
Shattering refers to the measure of how well the ripe kernel is attached to the spike,
as well as to what extent the husks covers and protects the kernel. Under both
irrigation and dryland conditions certain cultivars are more susceptible to bird damage
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and losses during harvesting. These cultivars must be considered with caution in
areas where birds are a potential threat.
Preharvest sprouting tolerance refers to the tolerance a cultivar has against
germination in the spike prior to harvesting. Under normal circumstances newly
released cultivars should not sprout in the spike. Spring types are more prone to
preharvest sprouting than winter types and some cultivars may also be more inclined
to do so than others under conditions of incessant rain during harvesting time.
Grading:
The grading of bread wheat is determined by hectolitre mass, protein content and
falling number. Environmental conditions such as heat and moisture stress during
grain filling and incessant rainfall during harvesting may affect the grade of the grain.
Management practices such moisture conservation and fertilisation may also make
significant contributions to the grade achieved. Although with the release of new
cultivars little deviation from the biological standard of grading characteristics is
allowed, there are genetic differences between cultivars for which the producer must
be prepared. Price differences between the various grades of wheat may negatively
affect the producer’s income per production unit if the cultivar does not compensate
with a higher yield.
Millers’ list:
The National Millers’ Chamber distributes its preference list on an annual basis. The
list must be taken into account during cultivar selection. All wheat cultivars marketed
by PANNAR appear on the millers’ preference list.
5. WHEAT CULTIVAR RECOMMENDATIONS
The selection of a suitable planting date is one of the aspects within the farmer’s
control. Unfortunately, the optimum planting date may vary over seasons due to the
complex interaction between the environment, soil and the plant. One of the most
important determining factors with regards to the optimum planting date is the soil and
air temperature. Good wheat germination will occur at a soil temperature of 4°C to
25°C. The maximum temperature for seedling development is 34°C while the
minimum is approximately -2°C. Thus, wheat is widely adaptable where seedling
development is concerned, which makes for a wide choice of planting dates.
The minimum temperature for leaf, stem and root development is 5°C while the
maximum temperature is 43°C with an optimum of 26°C. The temperate
requirements of the wheat plant during the spike development, pollination and grain
filling stages has a significant bearing on the choice of a suitable planting date as
temperatures outside the physiological limits at these stages may significantly affect
yields. Spike-elongation increases linearly when the air temperature increases from
10°C to 30°C. The optimum temperature for pollination is between 10°C and 25°C
with a minimum of 10°C and a maximum of 32°C. Temperatures outside these limits
result in yield losses due to pollen sterility and the deformation of the pistil and
stamens.
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In the summer rainfall region temperatures rise drastically during September and
October. During this period temperatures may rise higher than the physiological
tolerance limit of the wheat plant with associated yield loss. At the other end of the
spectrum, the reproductive stage is most sensitive to cold stress. When determining
the planting date for a particular cultivar, days to flowering must be taken into
consideration in order to lower the risk of frost occurrence during flowering.
Wheat cultivars are classified as winter, intermediate or spring types according to their
cold requirements. Winter wheat has a high cold requirement (vernalisation) that
must be met before it will produce grain. Spring types on the other hand have no cold
requirement and reach the flowering stage approximately 100 – 114 days after
planting. Wheat remains a cool-weather crop and cool weather conditions in
combination with sufficient moisture is favourable for the determination of yield
potential and optimal spike and grain filling of all wheat types. Winter types (long
growing season) must be planted early to meet their greater cold requirements.
Winter types tiller more readily and can therefore be planted at a lower plant density.
A major challenge for optimal dryland wheat production is the prevention of drought
and cold damage. The planting dates for each production area provided in the
PANNAR catalogue serve as guidelines and are no guarantee against frost and cold
damage. To keep the impact of such damage to a minimum, wheat must not flower
before the cut-off date of high frost risk in the various production areas, regardless of
the planting date.
As new, improved cultivars are released from time to time, it is recommended that the
latest PANNAR brochure or the local PANNAR Representative or Agronomist be
consulted for information regarding the most recent cultivars and recommendations per
production area.
Figure 2: Distribution of the Various Dryland Wheat Production Areas
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Figure 3: Introduction of the Wheat Production Regions under Irrigation
Irrigation areas
Cooler irrigation areas
Warmer irrigation areas
Mpumalanga
Eastern Free State
KwaZulu-Natal
Fish River
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C) SOIL PREPARATION
With the rising fuel prices, soil preparation has become the largest input in
wheat production. This has led producers to consider alternatives such as
chemical weed control to lower their input costs. Unpredictable weather
conditions make it increasingly difficult for wheat producers in the summer
rainfall region to establish a fixed recipe for soil preparation, due to the change
of climatic conditions. For these reasons, it is necessary for producers to plan a
preparation strategy with specific objectives in mind. Some of these objectives
include:
Conservation of groundwater – the most important objective for
successful dryland wheat production
Alleviate soil compactions – necessary for optimal water and root
penetration
Liming – neutralising of acidity
Seedbed preparation – firm seedbed for optimal seedling establishment
Weed control – to minimise moisture loss
Plant disease control – self-sown wheat or grass that may pass on
diseases.
Controlling of wind and water erosion
By striving for specific objectives, producers can try to keep the number of
preparations to a minimum. Soil preparation for small grains is divided into two
basic approaches, namely conventional tillage seedbed preparation and
conservation tillage seeding systems.
1. CONVENTIONAL TILLAGE SEEDBED PREPARATION
The conventional approach is recommended for a wheat-on-wheat
cropping system in which the risk of wind and water erosion is low and
there is a history of root diseases.
Step 1: Harvest December – January.
Step 2: Usually includes a preparation with a disk implement to
cut the rest of the previous harvest finer.
Step 3: Primary preparation with a plough. This preparation
must be carried out in the drier parts between January and the
end of February to ensure that sufficient rain falls on the ploughed
soil and supplements the groundwater. The timing of the
preparation will be determined by the groundwater and the
prospect of rain. The later this preparation can be postponed
due to a possibility of later rains, the fewer preparations are
necessary to control weeds and the less compaction will occur.
Step 4: The preparation is aimed at sealing the soil. It is carried
out by means of a harrow or a sweep cultivator.
Step 5: When necessary, weeds must be controlled with sweep
cultivator preparations. These preparations also serve as
seedbed preparation.
Step 6: Plant according to the guidelines. Where possible, use a
tined planter for the following reasons:
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1. Effective band placing of fertiliser in wet soils to improve the
uptake of nutrients.
2. Breaking up of shallow compact levels.
It is important that the spring pressure on planting equipment is adjusted
according to the soil conditions. The drier the soil, the heavier the pressure
that should applied; the wetter the soil, the lighter the pressure.
2. CONSERVATION TILLAGE SEEDING SYSTEMS
Conservation seeding systems are recommended in all areas where the rainfall
is low and where the risk of wind and/or water erosion is high as a result of the
low clay content of these soils. If conservation systems are implemented
(whether a high or low rainfall region) they should be applied in a crop rotation
system to minimise the risk of soil- or residue-borne diseases.
D) YIELD PLANNING
Step 1: Weed control (when wet enough) with a rolling rod or
sweep cultivator, depending on the amount of hay that must
remain on the surface.
Step 2: Deep cultivation with a tined implement, to break up
compact layers must be done in March or April. The timing
hereof must be of such a nature that the minimum further
preparation is necessary as each further preparation will
contribute to re-compaction and a loss of hay.
Step 3: Seal the soil directly after cultivation with a tined
implement with a sweep cultivator, harrow or V-blade.
Sept 4: Control weeds with shallow preparation (sweep
cultivator or V-blade) if necessary.
Step 4: Plant according to guidelines and preferably use a tined
planter.
The calculation of the planned yield is one of the first steps to successful wheat
production. The planned yield is defined as a realistic yield that is achievable
in the long term.
Important aspects to consider when calculating the planned yield include
the following:
Available groundwater at planting time. Determining factors include the
amount of rainfall and the distribution thereof before planting time, soil
preparation practices and soil characteristics (such as soil depth and
clay content which have an effect on water storage capacity and rooting
depth).
The amount of supplementary spring rainfall that can be expected.
The general production and management practices applied.
The long-term production history of the specific area.
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Now determine a realistic planned yield according to Table 1. Evaluate the
soil analysis in terms of fertilisation requirements and use the fertilising
guidelines for the specific situation to compile a fertilisation programme.
Table 1: Yield Potential for Dryland Wheat (kg/ha)
Expected rain after
planting 1 (mm)
Moisture depth 2 (cm)
30 60 90 120 150 180 3
10 0 0 158 460 763 1 065
20 0 0 259 561 864 1 166
30 0 57 360 662 964 1 267
40 0 158 460 763 1 065 1 368
50 0 259 561 864 1 166 1 468
60 57 360 662 964 1 267 1 569
75 208 511 813 1 116 1 418 1 720
100 460 763 1 065 1 368 1 670 1 972
1 Expected rain after planting refers to all the rainfall expected from planting
time until physiological maturation.
2 Moisture depth refers to the total depth that can be drilled using an auger or
dug using a spade (up to 1.8 m). The soil should be moist (not merely damp) at
planting time. Regardless of the soil texture, there should be 100 mm/m of
water available to the plant.
3 This table makes no provision for soil with a high water table.
E) FERTILISING GUIDELINES FOR WHEAT PRODUCTION
Fertilising guidelines aim to establish a frame of reference that can be used for
planning a fertilisation programme for a specific situation.
When fertilisation programmes are planned according to guidelines, it is
important that the following be kept in mind:
The prescribed guidelines must be seen as a frame of reference rather
than a recipe for a specific situation. Variations in soil, climate, soil
preparation and management may justify deviations from the guidelines.
These deviations must be motivated by facts.
It is accepted that production practices and managerial capacity is
maintained at a healthy level and that chemical and physical soil
conditions are not limiting factors.
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Soil analyses are necessary and should be carried out before every third
wheat harvest.
1. SOIL ACIDITY
Soil acidity is one of the principal influences for good or bad wheat
production in the summer rainfall area. Fertilisation programmes for
wheat can only be fully effective if the soil acidity does not impede soil
fertility. Acidic soil has a disadvantageous effect on the wheat plant due
to the associated high levels of aluminium in relation to other cations in
the soil. This results in excessive aluminium uptake, which is toxic to
the wheat plant. The root system of the wheat plant very clearly exhibits
the effect of aluminium toxicity. Typical symptoms include the thickening
of the root tips, brittle lateral roots and roots with a brown discolouration.
These symptoms indicate an ineffective root system which restricts the
uptake of water and plant nutrients. The affected plants show typical
drought and nutrient deficiency symptoms and may die off.
Guidelines for liming:
The pH (KCI) and the textural class of the soil are used to obtain an
indication of the lime requirements for wheat production. If the pH (KCI)
is lower than 4.5, pH (CaCl) lower than 5.0 or pH (H2O) lower than 5.5, a
complete analysis must be performed to determine the lime requirement.
The lime requirements are provided in Table 2. The concentration of
aluminium in relation to other cat ions in the soil plays an important role
in determines the reaction of the wheat plant. If the pH values are lower
that 4.5 and/or the percentage of acid saturation is greater than 8%, lime
should be administered.
Table 2: Lime Requirement (ton/ha) for Soils with Variable Acidity Levels
and Clay Contents 1
% Clay
∆ pH > 0.5
∆ AS > 32
∆ pH 0.5 – 0.4
∆ AS 32 – 23
∆ pH 0.4 – 0.3
∆ AS 25 – 15
∆ pH 0.3 – 0.2
∆ AS 15 - 10
∆ pH 0.2 – 0.1
∆ AS < 10
5 – 10 3.9 3.0 2.2 1.4 0.5
10 – 15 4.1 3.3 2.5 1.6 0.8
15 – 20 4.4 3.5 2.7 1.9 1.0
20 – 25 4.6 3.8 2.9 2.1 1.3
25 – 30 4.8 4.0 3.2 2.3 1.5
30 – 35 5.1 4.2 3.4 2.6 1.7
1 Information on determining the lime requirement as published by the ARC
Small Grain Institute in “Guidelines for the Production of Small Grains in the
Summer Rainfall region, 2006.”
Wheat production guide series Copyright 8 PANNAR SEED (PTY) LTD
∆pH – Change in the pH (KCI)
∆AS – Change in the % acid saturation
Soil with a pH of 4 and with a 12% clay content will, in this case, require
3.3 tons of lime per ha to attain a pH of approximately 4.5. If the lime
requirement is greater than 4 ton/ha, it must preferably be applied over
two production seasons. The equation below can also be used to
determine the lime requirement by inserting the desired change in pH
and the actual clay content.
Lime requirement = ∆pH*8.324+0.0459*clay-1.037
Cultivar selection as a short-term solution:
Given that wheat cultivars differ with regards to their levels of aluminium
tolerance, cultivar selection can be used to minimise yield loss. This
must be viewed as a short-term solution and producers must keep in
mind that although aluminium tolerant cultivars will perform better than
cultivars with a weak tolerance to acidic soils, tolerant cultivars also
respond positively to the application of lime. For classification purposes,
wheat cultivars are divided into three groups according to their
aluminium tolerance (Table 3). These groups are referred to as follows:
Excellent tolerance
Reasonable tolerance
Poor tolerance
Table 3: Classification of Wheat Cultivars According To Their Aluminium
Tolerance
Excellent tolerance Reasonable tolerance Poor tolerance
PAN 3355 GARIEP BAVIAANS
PAN 3377 PAN 3434
PAN 3349 PAN 3364
PAN 3118 PAN 3368
PAN 3120
2. NITROGEN FERTILISATION
Nitrogen fertilisation under dryland conditions:
In Table 4 the nitrogen fertilisation guidelines are outlined on a regional
basis as opposed to the planned yield. When using these guidelines,
the following important aspects must be kept in mind:
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All guidelines apply to the cultivation of a wheat crop after a
wheat crop with the assumption that all hay is worked back into
the soil.
Nitrogen fertiliser must be applied at planting time and surface
fertilising is not normally recommended.
High nitrogen fertiliser applied along with the seed may be
unfavourable to germination and therefore also to the final plant
stand. It is thus recommended that no more than 20 kg N/ha is
placed with the seed. Applications higher than 20 kg N/ha must
be applied shortly before planting time or band placed away from
the seed at planting time.
Cultivars with strong seedling vigour should be considered where
wind problems are experienced rather than adjusting the nitrogen
fertilisation to keep the wheat out of the wind.
Although theses recommendations are already adapted to ensure
that the protein content of the grain is satisfactory, adaptation can
be considered when new cultivars with a significantly higher yield
potential than the existing cultivar are planted.
Above average yields accompanied by higher volumes of harvest
residue may contribute to the occurrence of undecayed residue in
the soil at planting time. Late soil preparation and/or wet
conditions during soil preparation could cause a negative nitrogen
period and the associated weakened growth. This may result in
lower yields and downgrading due to lower protein content. With
the appearance or expectance of this situation, the fertilisation
programme must be adapted by increased nitrogen applications
at planting time, or the application of nitrogen (± 15 kg N/ha) and
lime (0.5 ton/ha) during late soil preparation to speed up the
breakdown process.
Table 4: Nitrogen Fertilisation Guidelines (kg N/ha) under Dryland
Conditions According To Production Area and Planned Yield in the
Summer Rainfall Region 1
Producing area
Southern Free State
North-west Free State
Central Free State
Planned yield Nitrogen fertilisation
(ton/ha)
Kg N/ha
1.0 10
1.5 15
2.0 25
1.0 10
1.5 20
2.0 30
2.5 45
3.0 55
3.5+ 2 65+
1.0 15
1.5 25
2.0+ 35+
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Table 4 (continued): Nitrogen Fertilisation Guidelines (kg N/ha) under
Dryland Conditions According To Production Area and Planned Yield in
the Summer Rainfall Region 1
Producing area
Eastern Free State
North-west
Mpumalanga
Limpopo (Springbok Flats
and Dwaalboom)
Eastern Cape coastal area
(East of Humansdorp 3 )
Planned yield
(ton/ha)
Nitrogen fertilisation
Kg N/ha
1.0 15
1.5 30
2.0 40
2.5 50
2.5+ 60+
1.0 5
1.5 15
2.0 25
1.0 10
1.5 20
2.0 30
2.5 40
1.0 0
1.5 10
2.0 15
1.0 15
1.5 20
2.0 30
2.5+ 45+
1 Information on area adaptations as published by the ARC Small Grain Institute
in “Guidelines for the Production of Small Grains in the Summer Rainfall region,
2006.”
2 Valid for the areas around Wesselbron – Viljoenskroon, where a high water
table and good moisture provision can lead to higher yield planning.
3 West of Humansdorp fits in with the winter rainfall area’s southern coastal area
where seed is sown.
Nitrogen fertilisation under irrigation:
Guidelines for fertilising under irrigation such as those included in Table
5 must be adapted when wheat is followed by a leguminous crop as well
as when large amounts of harvest residue is worked back into the soil.
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Table 5: Nitrogen Fertilisation Guidelines (kg N/ha) under Irrigation
According To Planned Yields 1
Planned yield (ton/ha) Nitrogen fertilisation (kg N/ha)
4 – 5 80 – 130
5 – 6 130 – 160
6 – 7 160 – 180
7 – 8 180 – 200
8 + 200 +
1 Information on Nitrogen fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
Under irrigation, applying nitrogen in instalments throughout the growing
season may realise higher grain yields and grain quality with reference
to protein content. A further advantage of applying nitrogen in
instalments is that the planned yield can be adapted throughout the
season depending on climate conditions, yield potential during a given
growth stage or on the water applications. The division of nitrogen
fertilisation across various yield targets on soil with a clay content of 15
– 25% is provided in Table 6.
Table 6: Distribution of Nitrogen Fertiliser throughout the Growth Season
at Various Yield Levels 1
Yield
(ton/ha)
Planting until
tillering stage
Nitrogen division (kg N/ha)
Tillering to
internode
elongation stage
Flag leaf to
flowering stage
4 – 5 80 – 100 30 0
5 – 6 100 30 30
6 – 7 100 – 130 30 30
7 – 8 130 – 160 30 30
>8 160 30 – 60 30 – 60
1 Information on Nitrogen fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
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On soils with lower clay percentages of 25%, the
divisions such as those in Table 6 can be followed.
The application of nitrogen during the flag leaf to flowering stage of plant
development is important to ensure that sufficient nitrogen is available
for kernel growth and development, and for acceptable levels of protein
in the grain. Depending on the yield potential, between 30 and 60 kg
N/ha must be applied in an attempt to increase the protein content of the
grain to above 11%.
3. PHOSPHATE FERTILISATION
There is a variety of phosphate analysis methods available. A
comparison of the analytical values obtained with the various methods
appears in Table 7. The approximate ratios such as those provided in
Table 7 will be valid for most soil types.
Table 7: Ratios (mg P/kg) Determined According To Various Analytical
Methods 1
Ambic 1 Bray 1 Bray 2
Citric acid
1:20
Olsen
6 6 9 10 4
8 10 13 15 6
11 14 18 20 8
13 17 22 25 10
16 20 26 30 12
20 24 31 35 14
23 28 36 40 16
26 31 40 45 18
30 34 45 50 20
1Information on phosphate fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
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Table 8: Phosphate Fertilisation Guidelines (kg P/ha) under Dryland
Conditions According To Planned Yield and Quality of Soil Phosphate
using the Bray 1 Analysis Method 1
Planned yield
Soil phosphate quality (mg/kg)
(ton/ha)
30
1.0 6 5 4 4
1.5 9 8 6 5
2.0 12 12 8 7
2.5+ 18 15
1 Information on phosphate fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
2 Minimum amounts that should be applied at the lower levels of soil phosphate.
With the interpretation of the phosphate fertilising guidelines for both dryland
and irrigation wheat, the following must be kept in mind:
With phosphate fertilisation, reference is made to citric acid or water
soluble sources.
Guidelines are compiled in accordance with economic principles and the
amount of phosphate fertiliser as included in the guidelines is the
amount on at which the maximum gross profit should be earned.
The guidelines make provision for a moderate accumulation of soil
phosphate at low levels of soil phosphate – if the wheat hay is not
removed from the land. A gradual, rather than a once off accumulation
process is supported by band placing phosphate fertiliser during the
planting process.
The higher phosphate fertilisation recommendations in the guidelines
correlate with the lower analytical values and vice versa. For the
analytical values between these limits, the correct phosphate fertilisation
must be deducted within the given amounts of phosphate fertilisation.
Under acidic soil conditions yield increases may be realized when
applying phosphate although high soil phosphate levels exist due to the
relatively lower availability of residual soil phosphate.
Table 9: Phosphate Fertilisation Guidelines (kg P/ha) under Irrigation
According To Planned Yield and Quality of Soil Phosphate using the Bray
1 Analysis Method 1
Planned yield (ton/ha)
Phosphate soil quality (mg/kg)
30
4 – 5 36 28 18 12
5 – 6 44 34 22 15
6 – 7 52 40 26 18
7+ >56 >42 >28 21
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1 Information on phosphate fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
4. POTASSIUM FERTILISATION
Local soils are reasonably rich in potassium and an increase in grain
yields is seldom realised by an increase in potassium fertilisation.
Conditions under which a potassium deficiency may appear include:
High alkaline sandy soil with low inherent soil potassium.
Cold and/or wet and/or dry soil conditions.
Very high content of magnesium and/or calcium levels in the soil.
Potassium fertilisation under dryland conditions:
The analytical values of soil potassium (as opposed to the planned yield)
are listed in Table 10 to illustrate the necessary potassium fertilisation.
The recommendation applies to soils with a clay percentage of >35%.
Where the clay percentage is
19
Table 11: Potassium Fertilisation Guidelines (kg K/ha) under Irrigation
According To Soil Potassium Status and Planned Yield 1
Planned yield (ton/ha)
1 Information on potassium fertilisation as published by the ARC Small Grain
Institute in “Guidelines for the Production of Small Grains in the Summer
Rainfall region, 2006.”
5. MICRO-ELEMENTS
Potassium analysis (mg/kg)
Table 12: Plant Analyses Values of Wheat at the Flag Leaf Stage 1
Element Low (deficient) Marginal High (sufficient)
N (%) 4.2
P (%) 0.5
K (%) 1.6
S (%) 0.4
Ca (%) 0.2
Mg (%)
21
Conditions during and just after application:
Environmental factors such as air moisture and plants that are under
stress are determining factors in the effectiveness of herbicides.
Favourable environmental conditions during spraying will oppose the
detrimental effect of antagonistic salts in the water. In contrast,
unfavourable conditions will compound the harmful effect of salt in the
water. Environmental conditions therefore play a large role in the uptake
of herbicides and the effectiveness thereof. Very poor weed control can
be expected when salt sensitive herbicides are mixed in poor quality
water and sprayed on stressed plants under low air humidity conditions.
Water volumes:
The higher the water volume per hectare with which the herbicides are
applied, the more salt there is to react with the herbicide. The opposite
applies with low water volumes. Although lower water volumes in theory
mean that the herbicide should work more effectively when there is salt
in the water, producers should rather adhere to the recommended water
volumes as far as possible.
Herbicide dose:
The dosage recommended on the label must be used.
Adjuvants:
On the labels of some herbicides the water quality is quantified in terms
of the pH of the application water. The pH is an expression of the
hydrogen-ion concentration in the water. If the herbicide is pH sensitive,
an efficient buffer or acidifier must be added until the optimal pH levels
are obtained.
Buffers or acidifiers are usually added to the irrigation tank before the
other components.
Threshold values:
As a guideline, antagonism can be expected if the combined calcium
and magnesium concentration of the water exceeds 100 mg/l (100
d.p.m.). The same norm can be used for the sodium concentration.
These threshold values are only estimates and depend on how the
abovementioned factors vary.
G) INSECT CONTROL
Wheat cultivation is subject to the appearance of various insect pests. Pests
not only differ in their economical importance, but the stage of development of
the wheat plant can also be a determining factor in deciding whether control is
necessary or not.
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1. APHIDS
The Russian wheat aphid is considered the most important aphid where
dryland wheat is cultivated, especially in the central and eastern Free
State. Aphids can reach plague proportions if the necessary control
measures are not in place. Other plant aphids such as the common
wheat aphid, oat aphid, brown ear aphid and rose grain aphid occur
sporadically and are seasonal in nature.
Russian wheat aphid:
The Russian wheat aphid is a small (30% which may occur on late/spring plantings in the eastern
Free State or under very dry conditions in the western parts of the Free
State. Re-infestation of wheat that was sprayed early may occur during
the susceptible period and subsequently need a follow-up spray, while
spraying after GS 12 is too late and damage will only be partially
avoided. The infestation levels at specific yield potentials that justify
spraying are shown in Table 13. There are seed treatments and
systematic soil agents registered for the control of early aphid
populations and some of these agents are effective for a period of
approximately 100 days.
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Resistant cultivar opposed to susceptible cultivar
Table 13: The Maximum Acceptable Infestation Levels at Various
Yield Potential Levels of Wheat
Yield potential (ton ha -1 )
Aphid infestation at GS 12
(% Plants)
>2.5 ≥4
2.0 – 2.5 ≥7
1.5 – 2.0 ≥10
1.0 – 1.5 ≥14
Other aphids: Aphids that appear sporadically in the summer rainfall
areas are the oat aphid, English grain aphid and rose grain aphid.
These aphids usually flourish under damp conditions and thick plant
densities that appear in irrigation fields, but may also appear during high
yield potential years under dryland conditions. The general guideline for
the application of control measures for these aphids is when 70% of the
tillers are infected with 5 to 10 aphids per tiller. In practice, these aphids
often only appear in severely infected spots within a land from where the
entire land can then be infected. Aphids are also often associated with
the carry over of viral diseases such as the yellow barley dwarf virus to
the wheat plant that in turn leads to the dwarfing and yellowing of the
plant and the consequent lowering in yield potential. Suggested
threshold values for the control of these aphids do not always take the
aforementioned into consideration. To ensure effective control and to
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avoid possible yield loss, the label prescription must be followed during
chemical control of aphids.
The oat aphid is a dark green, pear-shaped aphid with a reddish area
between the siphunculi on the rear end of the aphid, whereas the
English grain aphid appears in two forms, a brown and a green. The
prominent distinction here is that the siphunculi at the rear end are long
and pitch-black in colour. The rose grain aphid is light green in colour
with a dark green line on its back and the siphunculi are long and the
same colour as the body.
2. OTHER INSECT PESTS
Here follows a summary of insects that are regarded as secondary
plagues that appear sporadically on small grains in the summer rainfall
region.
Brown wheat mite:
The brown wheat mite is a small, dark brown, slightly oval shaped mite
with a pair of front legs visibly longer than the hind legs. Mites spend
the evening in or under the soil and inspections must be carried out
during the warm afternoon when the mites are normally most active.
Eggs are laid in the soil and remain dormant until the first light rains
appear in July to August. Dry conditions, after the eggs have hatched,
are favourable for the appearance of large numbers of mites. Speckled
leaves are an indication of infestation as the feeding mechanism of the
mite is designed to remove plant sap from the leaves. With severe
infestations, leaves may turn a yellow/ brown colour; chemical control
can be considered with the appearance of yellow and/or brown spots.
Damage caused by the brown wheat mite is more noticeable when the
plant is under stress. These conditions are detrimental to the uptake
and translocation of insecticides. Producers must be aware that rain
storms of 12 mm or more can drastically lower the mite population,
which makes chemical control unnecessary.
False wireworm:
The false wireworm is the larva of large, black coloured beetles with long
legs which allow them to run fast on the soil surface and hide under
plant material. The larva is the most damaging stage of this pest and
feeds on the seed, roots and seedling stems. Secondary infestation by
fungi such as Fusarium on damaged plant parts may lead to crown and
root rot. The false wireworm larva can be as long as 20 mm and is
distinguished by a hard, smooth body with a gold-brown to dark brown
colour and a sharp tail that points upwards. Seed treatments can be
effective where seedlings grow actively in moist soil.
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Bollworm:
The adult moths are light brown to grey in colour and have a wing span
of approximately 20 mm. The moths fly at sunrise and sunset and lay
their eggs directly on the plant. The young larvae of previous
generations feed on the chlorophyll of the leaves and later migrate to the
spike to feed on developing grain. The colour of the final stage larva
can vary from bright green to brown and it has a distinct white lateral line
on both sides. The larva can get as long as 40 mm and can cause
considerable damage. Direct as well as indirect yield losses can occur
on account of damaged grain with the consequent downgrading of the
grain. The presence of the bollworm is usually only noticed in the spike
when the larva reaches the mid-instar stage. Producers must regularly
inspect their lands for young larvae as the larger, older larvae are
usually less susceptible to insecticides and can cause considerably
more damage. Under dryland conditions, chemical control can be
considered when three to four larvae are found per walking meter.
Under irrigation, the threshold value is six to seven larvae per walking
meter. Only registered chemical agents must be applied and the label
instructions must be followed.
Black maize beetle:
The adult beetle is black, approximately 12 to 15 mm long with strongly
developed wings that enable the beetle to fly over long distances. The
female beetle lays approximately seven to ten eggs in the soil and the
larvae develop in three instars, followed by a pupal stage. The adult
beetles inflict the most damage. The larvae survive on organic material
in the soil. Beetles chew on the base of the seedling stem which causes
a decline in the stand. Given the mobility of the adult beetle, seed
treatment agents are registered as a pre-planting method of adult beetle
population management.
Leafhoppers:
The plague status of leafhoppers is greatly attributed to the fact that
these insects can transmit maize streak virus from infected maize or
certain grass species. Virus transmission usually occurs on early wheat
plantings that are planted near infected grass, maize or self-sown maize.
Young wheat plants that are infected with this virus have a dwarfed
appearance with curled leaves that have thin, well defined chlorotic lines
running parallel to the leaf veins. There are no chemical agents
registered for the control of leafhoppers on wheat. Infestation can be
avoided by later planting away from maize. The alternative is to
consider wheat cultivars that are tolerant to maize streak virus,
especially in areas or under practices where the risk of virus
transmission is high.
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H) DISEASE CONTROL
Fungal diseases on wheat can be controlled by planting resistant cultivars or by
the use of chemical agents. Chemical control can be applied when susceptible
cultivars are planted as well as when once resistant cultivars loose their
resistance due to the development of new pathogenic types of a specific fungal
disease with the ability to overcome the resistance mechanism of a cultivar.
The use of certified seed that is treated against seed-carrying diseases such as
loose and stinking smut also play an important role in the control of seedcarrying
diseases in wheat.
THE RISK OF FUNGAL INFECTION
It is very important that producers are aware of the risk of fungal infection in the
various production areas. The risk in high risk regions can be minimised by
including resistant cultivars in the cultivar package. When susceptible cultivars
are planted in high risk areas, producers must be aware of the disease
symptoms, favourable environmental conditions and threshold values for
chemical control of the various diseases.
Table 14: The Risk of the Occurrence and Outbreak of Rust Epidemics in
the Wheat Production Areas of the Summer Rainfall Region
Production area Stem rust Leaf rust Stripe rust
Western Free State LR 2 LR LR
Central Free State LR LR LR
Eastern Free State LR LR HR
KwaZulu-Natal HR 3
HR HR
Mpumalanga LR HR HR
Gauteng LR LR LR
Limpopo LR LR LR
Northern Cape LR LR LR
1 Where wheat is planted under full or supplementary irrigation the risk of the
development of leaf disease such as leaf rust and stripe rust is heightened.
2 LR = Low risk; 3 HR = High risk
CHEMICAL CONTROL OF FUNGAL DISEASES
A variety of fungicides are registered for the control of leaf diseases in wheat.
The active ingredients of the agents are divided into three groups, namely
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triazole, imidazole and benzimidazole. Rust and leaf-blotch diseases are very
effectively controlled by most triazoles. Certified seed is treated with
fungicides, which are registered as seed treatment agents for the control of
loose and stinking smut.
To successfully apply chemical control measures in wheat, producers
should take the following factors into account:
Climate conditions play a very important role in disease development.
Consecutive favourable periods for disease development will contribute
to disease progression and subsequent epidemic development on
susceptible cultivars. Most fungal diseases flourish in wet years when
there is good bio-mass development and the potential is high.
Chemical control must not be delayed unnecessarily when wheat is at
the flag leaf stage, especially with leaf diseases that progress rapidly,
such as stripe rust. The degree of cultivar susceptibility, yield potential,
growth stage and the incidence of the disease in the field or in the region
as well as prevailing climate conditions must be taken into consideration.
The residual effect of most fungicides that are applied as foliar sprays is
about three to four weeks. The efficacy of fungicides can be placed
under pressure when effective control is not achieved with spraying due
to poor spraying conditions or under conditions of continuous disease
pressure from nearby lands.
In the case where an earlier application (before the eight leaf stage) was
necessary, a second application may be necessary should the
environmental conditions continue to be favourable for disease
development after the three to four week residual effect.
Diseases are not all equally damaging and the economic importance of
diseases such as powdery mildew for example must also be taken into
account.
When wheat is planted in a high risk area of a specific disease,
consideration can be given to more disease tolerant or resistant
cultivars.
If a specific disease appears on a cultivar that is marketed as a resistant
cultivar it must be reported to the company involved. The appearance of
more severely infected spots of a disease such as stripe rust in a land
that is planted with a resistant cultivar, can suggest that the pathogen
overcame the resistance. Resistant cultivars must therefore, as with
susceptible cultivars, be monitored for the appearance of disease
symptoms.
Chemical control as seed treatment is often not effective against soilborne
diseases due to the extended growing period in which the wheat
plant is exposed to such soil-borne pathogens. Soil-borne diseases can
be managed by applying crop rotation and by ensuring that soil factors
such as compaction, which may place stress on the plant, is neutralised.
Self-sown wheat and wheat stubble that appears on the soil surface
often serve as carriers of leaf diseases.
Keep to the registered dosage and further label prescriptions to increase
the effectiveness of chemical control.
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ROOT DISEASES
Take-all (crater rot):
Take-all is an important root disease in wheat and is caused by a soil-borne
fungus. The disease is especially prevalent where wheat is cultivated in
monoculture systems under irrigation. During wet seasons take-all can also
appear on dryland wheat. Large yield losses can occur when the necessary
management practices are not in place to prevent take-all. The symptoms
include plants with fewer tillers, plants that die before the flowering stage and
the appearance of plants with white spikes in spots in the land. The roots and
crowns of infected plants are black in colour and break off easily due to the
rotting that has taken place. The risk of take-all can be reduced by crop
rotation with alternative crops such as lupin, canola and oats. Grass weeds
and other crops such as barley can also serve as carriers of the take-all
fungus.
Take-all at an advanced stage
Crown rot:
The disease emerges when fungi from the Fusarium genus infect the crowns of
the wheat plant and thereby causes crown rot. Although these fungi are
naturally present in soils, they will proliferate under a monoculture wheat
system. The first above-ground symptoms of this disease often only become
evident after flowering when tillers and spikes die off early. Crown rot mainly
emerges on dryland wheat that is under moisture stress. The disease can also
emerge secondarily on plants that are under stress as a result of primary root
infection by the take-all fungus. Spikes that die off early appear white and will
either not be filled at all or contain shrivelled grain. The crowns of infected
plants appear dark brown in colour and, with variable moisture conditions, the
leaf veins of infected crowns show a conspicuous pink to purple discolouration.
No chemical agent is registered against crown rot. Although all cultivars are
susceptible, there can be differences in their tolerance to crown rot. Crop
rotation and cultivation practices aimed at moisture conservation can lessen
the risk of the occurrence of crown rot.
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STEM, LEAF AND SPIKE DISEASES
Stripe rust or yellow rust:
The disease-causing fungus is an obligate parasite and can therefore only
survive on living plant material. This disease is airborne. Typical symptoms
include elongated, bright yellow to orange stripes which consist of rust pustules
that run parallel to the leaf veins. The stripe formation is less distinguishable
on the younger leaves and the rust pustules appear more in spots on the leaf.
Under very favourable conditions for the development of stripe rust, the leaf
veins, glumes, beards and young kernels can also be infected. The fungal
spores need moisture and low temperatures for germination and subsequent
infecting of susceptible plants. Areas with night and/or day temperatures of
less than 15°C which is coupled with regular dew, mist, rain or over-head
irrigation during the wheat season is regarded as a high risk area. Evening
temperatures above 15°C, with associated day temperatures of 25°C to 30°C,
will have an inhibiting effect on stripe rust development. Various triazolecontaining
agents are registered against stripe rust. Chemical control must be
applied after correct disease identification, confirmation of cultivar susceptibility
and with accompanying favourable environmental conditions for the spreading
of the disease.
Typical symptoms of stripe rust
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Resistant cultivar opposed to susceptible cultivar
Leaf rust or brown rust:
The leaf rust-causing fungus is air-borne and can be identified by the reddish
brown rust spots that appear on the leaves and leaf veins of the wheat plant.
This disease develops rapidly on susceptible cultivars when periods of dew or
misty conditions prevails which last longer than six hours with accompanying
temperatures of 15 to 22°C. During consecutive favourable periods for
infection the epidemic outbreaks can appear within a few weeks of the first
infection of susceptible cultivars. The risk of leaf rust can be managed by
cultivar selection. When chemical control is used, it is important to protect the
flag leaf.
Stem rust or black rust:
The fungus responsible for stem rust is air-borne and distinguished by the
appearance of large, elevated reddish brown rust spots on the leaves, leaf
veins, ears, beards and stems of susceptible cultivars. A more typical symptom
of stem rust is the appearance of elevated, oval shaped, reddish brown spots
on the wheat tillers and/or peduncle. Infection will take place when dew and/or
misty wet conditions are accompanied by temperatures of 15°C to 24°C. Due
to its preference for higher temperatures, stem rust usually appears later in the
season when the wheat plant is already in the grain filling stage. Under
favourable conditions for the development of stem rust an entire yield loss can
occur. The risk of rust infection can be minimised by planting resistant
cultivars. Chemical control of stem rust can only be successful if the tiller area
is covered properly with the fungicide.
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Severe infection of stem rust
Fusarium head blight:
Fusarium head blight is caused by fungi of the genus Fusarium where
Fusarium gramenearum is identified as the primary disease-causing organism
under local conditions. This disease is especially prevalent in irrigation
systems where wheat is alternated with maize, but can also occur during wet
seasons under dryland conditions. Infection of one or more glumes in the spike
during flowering and further spreading of the fungus to adjacent glumes can
cause parts of the spike turn white or "bleach" and die off early. The result is no
grain at all or small, shrivelled kernels on infected parts of the ear. Under wet,
humid conditions, there may be a pink discolouration of infected parts of the ear
due to fungal growth. Optimal conditions for infection and spreading include
temperatures between 15°C and 25°C accompanied by wet conditions and
relatively high humidity. The most effective way to avoid Fusarium head blight
is by crop rotation with non-host crops as well as the destroying of wheat and
maize stubble. Preventative ear spraying during flowering can help to lower the
infection to inhibit disease development.
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Fusarium head blight infection
Glume-blotch:
Glume-blotch is caused by a fungus and symptoms may appear on the leaves
and ears. The disease is found mainly in the eastern Free State and KwaZulu-
Natal. Lesions usually appear on older leaves, are brown, lens shaped and
encircled by necrotic and/or chlorotic leaf tissue. Depending on cultivar
susceptibility the symptoms may differ from cultivar to cultivar. A characteristic
symptom on the ears is the appearance of brown spots. Conditions favourable
for disease development include periods of six to seven hours of dew and/or
rain accompanied by high humidity and temperatures above 7°C. Glumeblotch
is at its most damaging when infection occurs between flag leaf
emergence and flowering. Cultivar resistance, crop rotation, removal of harvest
residue by ploughing or burning and chemical control can help to control the
disease.
Maize streak virus (“Kroeskoring”):
Maize streak virus is transmitted to wheat by leafhoppers from infected maize
and/or grass species. The symptoms on susceptible wheat plants are
described as “kroeskoring”. Plants that are infected at an earlier stage have a
dwarfed appearance and will form fewer tillers with smaller spikes. Chlorotic
lesions that form on infected leaves later converge to form well defined yellow
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lines that run across the length of the leaf. Resistant or more tolerant cultivars
can be used to limit the damage caused by the maize streak virus.
Powdery mildew:
Symptoms of powdery mildew include white to grey cotton-like fungal growths
on aboveground plant parts. This fungal disease typically occurs on the leaves
of the plant, but may also be found on the stems and the spikes under epidemic
conditions. The disease will progress under cool, cloudy and humid
environmental conditions as well as within a dense plant population. Cool
temperatures (15°C to 22°C) and cloudy, humid conditions are ideal for the
development of powdery mildew. The disease can cause yield loss if infection
takes place at an earlier stage and conditions remain favourable for the
development of epidemic conditions before spike development.
SMUT
Karnal bunt:
Karnal bunt is caused by a smut fungus and is seed- as well as air-borne. This
disease is currently limited to irrigation areas of Douglas and Prieska.
Favourable conditions for the development of Karnal bunt include day
temperatures of 16°C to 23°C and night temperatures of 7°C to 11°C. A
relative humidity of more than 70% or a minimum relative humidity of more that
48%; rainfall or irrigation over a few consecutive days during spike
development will also contribute to infection. Typical symptoms include
infected kernels with a black appearance due to the presence of teliospores, a
distinctive weathered appearance and the smell of rotten fish. For the control
of Karnal bunt, it is important that producers use certified seed. Seed can be
treated with Anchor Red (active ingredient is carboxin). This fungicide has the
ability to kill spores which serves as a precautionary measure. Spike spraying
with triticonazole (Tilt ® or Bumper ® ) during the appearance of the spike can
suppress infection to acceptable levels. The first application must be applied at
25% spike appearance with a follow-up spray 10 days later.
Loose smut:
This fungal disease appears in all wheat production regions. Typical symptoms
of loose smut can be observed after spike appearance. Infected spikes are
visible as black to dark brown spore masses which have replaced the spikelets.
When spores have been blown or washed away only the rachis remain. Loose
smut development is favoured by cool, humid environmental conditions which
lengthen the flowering period of the plant. This disease can be avoided by the
use of certified seed that has been treated with a fungicide.
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Loose smut after ear appearance
Stinking smut:
Stinking smut occurs in all wheat production regions. The typical symptoms
are visible after spike appearance when kernels are replaced with greyish
brown coloured “bunt balls”. The smut ball consists of a mass of fishy-smelling
powder (spores of the stinking smut fungus). Infected spikes may also take
longer to ripen. Stinking smut can be avoided by the use of certified seed that
has been treated with the necessary chemicals.
I) GRADING AND QUALITY
Currently, according to the law on agricultural products, there is one bread
wheat class with four grades, namely B1, B2, B3 and B4, which is determined
according to the protein content of the grain, the hectolitre mass and falling
number (Table 15). Hectolitre mass and protein content are largely determined
by the area which includes management practices. Hectolitre mass as a
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density parameter gives a direct indication of the potential flour extraction of the
grain sample. The flour extraction is a critical parameter for the miller since it
has an influence on his/her profitability. A high protein content as well as
protein quality is necessary to ensure that the baker can successfully bake
bread that satisfies consumers’ requirement. Falling number is an indication of
the α-amylase enzyme activity in the grain. A high α-amylase activity (low
falling number) is an indication that the starch molecules have already been
broken down into sugars (maltose) to a large extent and such grain in large
volumes is unacceptable for baking purposes.
Table 15: A Schematic Introduction of the Various Classes and Grades of
Bread Wheat
Grade
BREAD WHEAT – CLASS B
Minimum
protein
(12% moisture
base)
Minimum Hlm
(kg/hl)
Minimum falling
number
(Seconds)
B1 12 77 220
B2 11 76 220
B3 10 74 220
B4 9 72 220
Utility 8 70 150
Other class
J) BIBLIOGRAPHY
Anonymous, 1989. Guidelines for crop production. General cultivation of
wheat.
Anonymous, 1989 – 1990. Guidelines for crop production. Fertilisation
guidelines for wheat production.
Anonymous, 1989 – 1990. Guidelines for crop production. Pest control in
wheat.
Anonymous, 1992 – 1993. Guidelines for crop production. General cultivation
of wheat. Co-ordinated instructions: Planned yield of wheat.
Anonymous, 1992 – 1993. Guidelines for crop production. Fertilisation
guidelines for wheat production.
Anonymous, 2006. Guidelines for the production of small grains in the summer
rainfall region. Composed by the ARC Small grain institute, University of the
Free State and SAB Maltings (Pty) Ltd.
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