Primary symptoms

Excessively high or low temperatures or moisture stress at heading indicate a possible problem of sowing date. Wheat is most sensitive to temperature and water stress during the flowering and heading stages.

Sowing at the wrong time exposes the crop to temperature and moisture extremes.

Summary

There is an optimum time for sowing for every location determined primarily by weather and availability of the field and irrigation water, but also by the variety that is being used and the likely timing of serious disease in the area. The best sowing time is that which gives the highest yield within the local limitations. It is usually decided on by working backwards from the date that is best for anthesis (see points listed below). Once the best sowing time has been determined, any delays in sowing at that date can reduce yield. Yield loss from delays will generally be greater in hotter regions.

The most suitable variety will be one that fits its growth stages into the available time. When deciding on variety and calculating your sowing date you should bear in mind the following risks:

• Frost from spike emergence (Z5.1) through early grain filling should be avoided.
• High temperature during anthesis and early grain filling is best avoided.
• Avoid very overcast and misty conditions during 2 weeks before to 1 week after anthesis - solar radiation should be high for this period.
• Irrigation water should be available from stem elongation through anthesis to early grain filling.
• Avoid varieties that run to head too quickly before producing tillers unless the available season demands a very short duration crop.

Think not only of the current crop. Work out the best compromise planting times for all sequential crops in the rotation so that annual production is optimised.