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The decision to spray petals to prevent sclerotinia stem rot depends on 3 key questions:
1) Have conditions been moist over the past few weeks for apothecia development and survival?
2) Is the canopy thick and is yield potential high?
3) Does the forecast call for more rain and/or humidity in the next week?
If the answer is “yes” to all 3, it’s a no brainer to spray. If only 2 questions have “yes” answers, then the decision is more difficult. Consider canola price and overall profit potential of the crop before investing more in it. Canola with yield potential of less than 30 bushels/acre is not likely worth spraying. Crops with an open canopy could be at lower risk, particularly if warm and windy weather allows them to dry out in the afternoons. However, if frequent rains and high humidity keep the plants wet there is still a threat.
Does hail raise the sclerotinia risk? Broken stems and leaves along with lodging after a hail may increase the risk of sclerotinia stem rot infection. Regrowth after a hail may also extend the flowering period, which also increases the sclerotinia risk. But should a grower automatically spray fungicide on a hailed crop? That depends. If yield potential is still high and if conditions favourable to sclerotinia stem rot persist, then a fungicide spray may pay off.