John Basera and Tegwe Soko Time of Planting
The optimum time for planting winter wheat is between mid-April and the last week of May and even earlier in the Lowveld.

Sometimes planting time can be extended to mid-June but not normally recommended. Delayed planting results in a loss of about 50kg/ha/day after May.

The first two weeks of May tend to give the best yields in the Highveld areas.

Adhering to the optimum planting time has some agronomic benefits:

Early summer rain escape: Rains which come after the wheat has reached physiological maturity causes pre-harvest sprouting (grain germination in the ear) and results in down grading of the wheat due to a decline in baking qualities

Disease escape: Disease pressure especially for rust diseases, normally rises when temperatures start to warm up around August and an early planted crop would have gotten a good head start without disease pressure.

Pest escape: Likewise pest pressure, such as aphids, begin to increase when temperatures start to rise. An early planted crop will have a good head start ahead of pest pressure.

Early planting will result in early harvesting around September. One of the key considerations for the adoption of double cropping is early planting and early harvesting for both summer and winter crops. The farmer will come in with his summer crop on time when wheat is planted and harvested early.

Wheat critical stages such as crop establishment, tillering, flowering and grain filling will coincide with the optimum growth conditions when the crop is early planted. For instance, for robust tillering i.e. for the plant to produce secondary stems (4 – 5 weeks after crop emergence) requires very cool conditions that normally occurs in May and June while Flowering (60 – 90 days) and Grain filling (> 90 days) must not coincide with frosty conditions to avoid crop sterility.

Seeding Rates and population density management

The optimum plant population for wheat is 220-250 plants per square meter. Seed rate depends on the seed size, germination percentage, planting conditions and planting method. To achieve optimum population density, a seeding rate of about 125 kg/ha when drilling and 135-140 kg/ha when broadcasting. To ensure good crop standability and yield, farmers should adhere to these optimum population densities. Diseases such as Powdery Mildew are also minimized with adherence to optimum population levels.

Irrigation requirements and scheduling

The total gross amount of water required is up to 600 mm per ha (i.e. 6 mega litres per ha) depending on method of irrigation and must be applied as the crop requires it.

The key points are:

the soil must be brought to field capacity to the full potential rooting depth (about 1,2 m) at planting to emerge the crop;

a light irrigation must be applied at the 4th or 5th day after sowing, to remove soil capping and to ensure good crop emergence

a light irrigation must be applied at 14 to 17 days after emergence to stimulate crown root development and tillering.

irrigation thereafter must be applied to match crop water use. On sandy soils with low water holding capacities, irrigate frequently (7 to 9 day cycles with 30-35mm net).

On clays and sandy clays, with good water holding capacities, irrigation may be less frequent with larger amounts (10 to 14 day cycles with 40-45 mm net).

This is a general irrigation scheduling guide. For an informed irrigation scheduling, the use of a soil auger to evaluate the soil water content ahead and behind the irrigation line is a good aid to irrigation management.

Irrigation is terminated when the neck of the ears/spikes/head (peduncle) turn yellow ie physiological maturity.

Schedule irrigation at particular wheat crop growth stages. These for the Highveld are;

i. Germination and crop emergence

ii. Crown root development and tillering (3 – 4 weeks)

iii. Appearance of the first node and start of shoot elongation (6 – 7 weeks)

iv. Booting and flag leaf emergence (9 – 10 weeks)

v. Ear emergence and anthesis (Flowering) at about 12 weeks

vi. Grain filling from 13 – 15 weeks

Note that two most critical growth stages for wheat are crown root development and from booting (first node) to milk dough stage and scheduling should carefully target to suffice water requirements at these stages.

Crop hardening

This is when irrigation is temporarily withdrawn for 10 to 14 days in light and heavy soils respectively. After the crop has emerged, the hardening stage begins.

This induces crown root development as well as tillering.

Top dressing fertiliser and herbicide application is done after a light irrigation which follows the hardening period, generally about 21 days after emergence.

Fertilisation

The fertiliser regime management in wheat, like any other crop, must be tailored to the soil fertility status; the yield potential; and the grain quality requirements. Always sample soils for analysis to determine amount and types of fertiliser before crop establishment.

As a general guide, wheat requires a basal application of 300 to 500 kg/ha of a compound fertiliser (such as 7-14-7) and blends and a top dressing of 350 to 500 kg of Urea or Ammonium Nitrate per ha.

Basal dressing is broadcasted and incorporated before sowing. Generally, a total of 160 -190kg/ha of Nitrogen Units (N), 50 – 70 units of Phosphorous (P) and 30 – 50 units of Potassium (K) is adequate for optimum yield.

Top dressing is broadcasted after the hardening period.

The top dressing is usually applied in one application between 14 – 21 days after emergence on heavy soils, and in two applications of equal amounts at 14 and 35 days after emergence on sandy soils by broadcasting.

Top dressing is essential for good leaf and general plant growth and ultimately the yield but also importantly for attaining good protein levels.

Application of Nitrogen after flowering can also boost the Grain Protein Content of wheat.

All fertility management practices must be based on proper full soil analysis recommendations by approved laboratories.

Weed control

Farmers are advised to apply wheat specific post-emergence herbicides after a light irrigation which follows the hardening period (2 Weeks After Crop Emergence).

Pest and disease control

Aphids and stalk borers can attack wheat with aphids coming in early, soon after tillering, while borers can attack the plant from flowering onwards.

Farmers must also be on the look-out for “Fall armyworm” given that wheat is one of the host crops to the pest. These pests can be controlled with appropriate pesticide sprays after scouting.

During the late grain-filling period, Quelea birds may consume much grain and reduce yields significantly if not attended to. A pesticide called 9,10-Anthraquinone 50% WP (Bird Shield) has been developed, which can be used as a seed dressing or as a foliar spray at soft dough stage.

Efficacy of this pesticide molecule can be enhanced by applying with a sticker and also a rain-free period of at least 4 hours. This pesticide molecule will act as a bird repellent. This is the best and the most efficient option against Quelea.

The other option is bird-scaring using bells, tins, whistles, discs/reflectors etc. by bird scaring gangs.

Diseases such as Leaf Rust, Stem Rust, Powdery Mildew, Fusarium Head Blight and Take-All may cause significant yield reduction if not controlled. Farmers must seek professional advice on chemical control options of these diseases.

It is advisable to grow resistant varieties that are available in order to reduce fungicide costs and minimise environmental damage due to chemical use.

Be a crop doctor

A crop doctor is a farmer who takes time to investigate his fields in order to prevent problems and improve productivity. He walks his fields regularly, observing, thinking, inspecting and evaluating. He diagnoses problems and seeks solutions.

John Basera-Seed Co Agronomy and Extension Services Manager

+263 772 413 184/ [email protected]

Tegwe Soko-Seed Co Group Wheat and Small Grains Program Lead

+263 772 516669/[email protected]