Canola-High Temperatures and Drought

Heat injury to seedlings occasionally occurs on hot sunny days, with air temperatures in the range of 85-95 F and soil temperatures of 120 F have been recorded. Heat injury is commonly associated with drought injury, but excessive heat will also injure or kill plants even if moisture is plentiful.

When in the blooming stages, heat blasting and or flower abortion is a strong possibility. This can vary from field to field and is very dependent on time of flowering, soil moisture and humidity during the hot periods. Usually in this situation one would see no or limited pod growth and thus no seed. It will usually be in patches on the main stem and branches as related to time of flowers and the heat stress. With good soil moisture under canola usually flower abortion will be minimized. 

Both low and high temperatures can adversely affect development prior to and during flowering. Low, but non-freezing, temperatures just prior to flowering slow the rate of plant development. The start of flowering is delayed or, if begun, the rate of flower opening is slowed and the amount of pollen shed is reduced. High temperatures at flowering will hasten the plant's development, reducing the time from flowering to maturity. High temperatures during flowering shorten the time the flower is receptive to pollen, as well as the duration of pollen release and its viability. This can decrease the number of pods which develop and the number of seeds per pod, resulting in lower yields. It appears that Brassica rapa (Polish) is more susceptible to this type of damage than Brassica napus (Argentine). Very hot weather combined with drought may cause bud blasting wherein the flower clusters turn brown and die resulting in serious yield losses.

Once pods are formed, canola is more tolerant than at flowering to high temperatures. Cool night temperatures at this time also help the plant recover from extreme heat or dry weather.

However, during this stage, a combination of heat and extreme drought will severely affect the pod and seed development including formation of seeds, seed size and oil content. The seed oil content is highest when seeds mature under lower temperatures (50 to 70 F). High temperatures during seed maturation result in reduced oil content. High temperatures, drought and long days hasten maturity and in combination, can reduce yield through fewer pods, with fewer lighter seeds per pod.