Wheat Production Guides - Pannar · PDF file2 B) CULTIVAR INFORMATION – FIRST STEP TO SUCCESSFUL WHEAT PRODUCTION 1. INTRODUCTION Cultivar selection is one of the most important

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

1

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

2

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.

3

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 AI3+ 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

4

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.

5

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.

6

Figure 2: Distribution of the Various Dryland Wheat Production Areas

Irrigation areas Cooler irrigation areas

Warmer irrigation areas

Mpumalanga

Eastern Free State

KwaZulu-Natal

Fish River

7

Figure 3: Introduction of the Wheat Production Regions under Irrigation

8 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:

Wheat production guide series Copyright 8 PANNAR SEED (PTY) LTD

9 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.

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.

D) YIELD PLANNING

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.


10 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 planting1 (mm)

Moisture depth2 (cm)

30 60 90 120 150 1803

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

1Expected rain after planting refers to all the rainfall expected from planting time until physiological maturation. 2Moisture 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. 3This 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.


11 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 Contents1

% 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

1Information 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.”


12 ∆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:


13 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 Region1

Producing area Planned yield

(ton/ha) Nitrogen fertilisation

Kg N/ha

Southern Free State 1.0 10 1.5 15 2.0 25

North-west Free State

1.0 10 1.5 20 2.0 30 2.5 45 3.0 55

3.5+2 65+

Central Free State 1.0 15 1.5 25

2.0+ 35+


14Table 4 (continued): Nitrogen Fertilisation Guidelines (kg N/ha) under Dryland Conditions According To Production Area and Planned Yield in the Summer Rainfall Region1

Producing area Planned yield

(ton/ha) Nitrogen fertilisation

Kg N/ha

Eastern Free State

1.0 15

1.5 30

2.0 40

2.5 50

2.5+ 60+

North-west

1.0 5

1.5 15

2.0 25

Mpumalanga

1.0 10

1.5 20

2.0 30

2.5 40

Limpopo (Springbok Flats and Dwaalboom)

1.0 0

1.5 10

2.0 15

Eastern Cape coastal area (East of Humansdorp3)

1.0 15

1.5 20

2.0 30

2.5+ 45+

1Information 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.” 2Valid for the areas around Wesselbron – Viljoenskroon, where a high water table and good moisture provision can lead to higher yield planning. 3West 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.


15

Table 5: Nitrogen Fertilisation Guidelines (kg N/ha) under Irrigation According To Planned Yields1

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 +

1Information 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 Levels1

Yield (ton/ha)

Nitrogen division (kg N/ha)

Planting until tillering stage

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

1Information 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.”


16

On soils with lower clay percentages of <15%, nitrogen applications can be further subdivided during planting and the tillering stage, depending on the practicality thereof such as whether the irrigation equipment is adapted for applying nitrogen. When the clay percentage is >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 Methods1

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.”


17

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 Method1

Planned yield

(ton/ha) Soil phosphate quality (mg/kg)

<52 5 – 182 19 – 30 >30 1.0 6 5 4 4 1.5 9 8 6 5 2.0 12 12 8 7

2.5+ 18 15

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.” 2Minimum 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 Method1

Planned yield (ton/ha) Phosphate soil quality (mg/kg)

<10 10 – 18 19 – 30 >30

4 – 5 36 28 18 12

5 – 6 44 34 22 15

6 – 7 52 40 26 18

7+ >56 >42 >28 21


18 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.” 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 <35%, only maintenance fertilisation is needed. Potassium can be band placed in a mixture with nitrogen and phosphate.

Table 10: Potassium Fertilisation Guidelines (kg K/ha) under Dryland Conditions According To the Soil Potassium Status and Planned Yield1

1Information 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.”

Potassium Fertilisation under irrigation: Potassium fertilisation guidelines for irrigated wheat are provided in Table 11 according to the soil potassium status and planned yield. Potassium fertiliser can be broadcasted and worked in as a mixture with nitrogen and phosphate. Potassium application can be divided throughout the growing season on soil with a clay percentage of <35% to ensure continuous availability on the topsoil.

Planned yield (ton/ha) Potassium analysis (mg/kg)

<60 61 – 80 81 – 120* 120+

1 – 2 20 15 15 0

2 – 3 30 20 20 0

3+ 40 25 25 0


19

Table 11: Potassium Fertilisation Guidelines (kg K/ha) under Irrigation According To Soil Potassium Status and Planned Yield1

1Information 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

Micro-elements play an essential role in the physiology of the plant. Deficiencies can lead to underdevelopment and non-functioning, which could lead to yield losses. Micro-element deficiencies also have distinctive symptoms. Symptoms indicate that the damage has already been done, whether a decrease in biomass at an earlier growth stage or yield losses at more advanced growth stages. However, if deficiencies can be rectified early, yield loss can be kept to a minimum. Micro-elements are not generally recommended under dryland conditions given that the risk of cost recovery is too large. In cases where micro-elements are in fact the yield limiting factor, especially under irrigation, and the specific deficiency is justified by means of a plant analysis, rectification can be considered. A summary of plant analytical values for the various micro-elements at the flag leaf stage follows in Table 12. Moderate deficiencies can be corrected with a single leaf spray between the stooling and flag leaf stages. When significant deficiencies appear, a second spray should be applied at the flag leaf stage.

Planned yield (ton/ha) Potassium analysis (mg/kg)

<60 61 – 80 81 – 120* 120+

4 – 5 50 25 25 0

5 – 6 60 30 30 0

6 – 7 70 35 35 0

7+ 80 40 40 0


20 Table 12: Plant Analyses Values of Wheat at the Flag Leaf Stage1

Element Low (deficient) Marginal High (sufficient)

N (%) <3.4 3.7 – 4.2 >4.2

P (%) <0.2 0.2 – 0.5 >0.5

K (%) <1.3 1.5 >1.6

S (%) <0.15 0.15 >0.4

Ca (%) <0.15 0.2 >0.2

Mg (%) <0.1 0.15 0.15 – 0.3

Cu (mg/kg) <5 5 – 10 10

Zn (mg/kg) <20 20 – 70 >70

Mn (mg/kg) <30 35 – 100 >100

Fe (mg/kg) <25 50 – 180 >180

Mo (mg/kg) <0.05 0.05 – 0.1 >0.1

B (mg/kg) <6 6 – 10 10

1Information on plant analytic values of wheat as published by the ARC Small Grain Institute in “Guidelines for the Production of Small Grains in the Summer Rainfall region, 2006.”

F) WATER QUALITY AND WEED HERBICIDES

Costs related to weed herbicides include product cost and cost of application. To ensure that the product works effectively, producers should eliminate aspects such as salt antagonism that may have a detrimental effect on the effectiveness of the product. 1. FACTORS THAT AFFECT THE SALT ANTAGONISM OF

HERBICIDES: Sensitive herbicides: Producers must be aware that only certain herbicides are adversely

affected by salt in the water. These products mainly include post-emergence herbicides such as glyphosate-containing agents, hormone herbicides and certain products from the sulfonylurea group. The reason for poor weed control is that antagonistic salts in the application water may affect the amount and speed of uptake of the herbicide by the weed’s leaves. By regarding all herbicides as candidates for antagonism and by applying all the necessary precautions, the risk of poor control is limited. Herbicides must therefore always be mixed with clean water, which means that muddy water should preferably not be used for chemical spraying.


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.


22 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 (<2.0 mm), spindle shaped; light yellow-green to grey-green aphid with very short antennae and a double tail. Until 2005, only one biotype of this aphid, namely RWASA1, had been recorded in the Free State. A more harmful Russian wheat aphid was identified in 2005 when crop damage (and the associated yield loss) was experienced despite cultivating varieties with genetic resistance to the original RWASA1. The planting of once resistant cultivars is therefore no guarantee against infestation and producers will have to consider alternative control measures to avoid damage. The two biotypes cannot be differentiated with the naked eye and producers must rather concentrate on the nature of the plant’s reactions. The leaves of susceptible young plants roll up tightly and lie flat on the ground. Familiar, elongated white to white-yellow lines appear on the leaves of larger plants which sometimes turn purple after cold weather conditions. The leaves are rolled up tightly and the ears may be squashed during development. In contrast, only small white and yellow blotches and/or spots appear on the leaves of resistant plants and the leaves usually do not roll up tightly. Wheat fields should be regularly monitored to determine whether chemical control is to be applied or not.

The wheat plant is most susceptible to damage by the Russian aphid between the start of the flag leaf stage (GS 14) until complete spike development (GS 18). To avoid yield loss, the top two leaves must be protected against infestation. This is accomplished by spraying at GS 12. Spraying before GS 12 is only recommended in cases of severe infestation >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.


23

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


24 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.


25 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.


26 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 seed-carrying 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 LR2 LR LR

Central Free State LR LR LR

Eastern Free State LR LR HR

KwaZulu-Natal HR3 HR HR

Mpumalanga LR HR HR

Gauteng LR LR LR

Limpopo LR LR LR

Northern Cape LR LR LR

1Where 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. 2LR = Low risk; 3HR = 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


27 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 soil-borne 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.


28 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.


29 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 triazole-containing 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


30

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.


31

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.


32

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. Glume-blotch 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


33 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.


34

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


35 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

BREAD WHEAT – CLASS B

Grade

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.

Documents

Wheat Production Guides - Pannar · PDF file2 B) CULTIVAR INFORMATION – FIRST STEP TO SUCCESSFUL WHEAT PRODUCTION 1. INTRODUCTION Cultivar selection is one of the most important