Hail on seedlings: Early season hail rarely has an impact on canola yield potential. Hailed seedlings usually come back very well. If hail breaks off both cotyledons or snaps the stem, these plants usually do not survive. But even in these severe cases, while individual plants may die, a whole canola crop is fairly resilient to early season hail when it comes to overall yield potential.
An average stand can be reduced to fewer than 40 plants per square metre (4 per square foot) before yield losses exceed 10%. The crop recovers its yield potential because the remaining seedlings take advantage of the reduced competition for light, moisture and nutrients. As a result, plants grow larger, produce more branches, and develop more pods and seeds per pod, compensating for the lost plants. However, with fewer plants, crop maturity can be delayed, and maturity throughout the field can be more variable between hailed and unhailed plants. This can present challenges for fungicide timing for sclerotinia stem rot and harvest timing, for example.
Hail on 4- to 6-leaf plants: The later hail occurs, the higher the chance of yield loss, given that the plants have less time to recover. Plants at the 6-leaf stage, for example, that lose most of the leaf area on the main stem can still live, but these leaves will not regrow. The plant will be delayed, and more of the yield potential — which will be lower than before the hail — will come from side branches.
There is no evidence that foliar nutrition or fungicides will help the recovery. However, we do know that crops hailed at this 4- to 6-leaf stage or earlier can get more blackleg. Fungicide might help, but use it only if you were considering using it in the first place. If the field was already at high risk of blackleg, hail damage increases that risk. If blackleg was not a major risk, fungicide probably won’t help much. Blackleg lesions on leaves or pseudothecia on canola residue are indicators of risk.
Losing leaves also represents an immediate loss of nutrient reserves within the plant. A top dress of nitrogen fertilizer to be taken up by the roots may compensate, but keep in mind that the yield potential of the crop is also lower — so the question is how much more do you want to invest in this crop?
An important step with hail damage at any time of the season is to call your hail insurance provider and keep them in the loop.