Sclerotinia management: What is 20% flower?

Fungicide to protect the crop from sclerotinia stem rot infection must be applied to petals before infected petals start to drop into the canopy. Petal drop starts after 30% flower, so the best time to apply is at or just prior to 30% flowering to cover as many flowers as possible. This is assuming conditions have been suitable for spore production and sclerotinia infection at this early flowering stage.

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.

To assess flowering progress, concentrate on the main stem only. Count all flowers, including aborted flowers and developing pods.
—15 flowers main stem, the field is around 20% flower.
—20 or more flowers on the main stem, the field is at roughly 50% flower. This is when the field is at its most yellow.

Click here to read NDSU’s complete factsheet on sclerotinia stem rot management and canola flowering stages.