Hot days (28-30°C and up) and warm nights (16°C and up) from bud to mid-flowering stages can have a significant effect on canola yield. Cool nights offer some recovery from hot days. Warm nights do not provide a recovery period, and more flowers are aborted, producing blanks along the stem. Even with a few days of heat, it can take a week for hormone balance and regular pod formation to return. Most years, seeding early so canola flowers during cooler parts of the summer is an effective strategy for higher yields. Recently opened flowers with shortened stamens that don’t protrude above the petals can be a sign of heat damage. Click here to see Murray Hartman explain how heat affects canola reproduction.
How to ID heat damage? Heat is one cause for missing or stunted pods at the top or middle of stems. Heat can also cause pods to appear green on the ends and translucent in the middle. Other causes for missing pods.
Does boron help? One Ontario study showed that a foliar boron application may improve flower retention in hot conditions, but the yield benefit was marginal. An economic benefit from this application on the Prairies is not likely. A situation where boron may provide a return is when it’s added into a fungicide mix (when the fungicide is deemed necessary) for canola in sandy soils where there have been definite boron deficiency symptoms in the past. The combination of extended flowering and poor yield is often the result of boron deficiency. Check product labels before mixing boron with fungicide.