Earliest canola is starting to flower this week, which means the sclerotinia spray decision looms. Spray timing, if a grower decides to go for it, should be within the window from 20% to 50% bloom. (Some products are registered for only 20% to 30% bloom.) At 20% bloom, no petals have dropped and no pods are forming. At 30% bloom, petal drop has just begun and side branches are just starting to bloom. Canola can reach 20% flower in 4-5 days after first flower, so prepare to assess the sclerotinia stem rot risk as soon as flowering starts.
Boron. We have limited research on the benefits of a boron application at flowering. Ontario research is inconclusive on the benefits of boron, which is often applied in southern Ontario to help reduce flower abortion during summer heat waves. Tank mixing boron with a fungicide in the sclerotinia window will reduce boron application costs, but check with fungicide companies about compatibility.