Nutrient and fungicide top dress treatments have been promoted to help heal and restart canola after hail. We don’t have published studies on using these or any treatments for this purpose in Western Canada, so it’s buyer beware. Leave a check strip to see if they improved yield.
For products that require foliar uptake to work properly, severe hail damage may have striped the leaves, reducing the surface area available for absorption by the plant.
Top dressing N and S on hailed crop. Nitrogen and sulphur are taken up through roots, for the most part, and so lost leaf area is not a concern for uptake. A treatment of 10-15 pounds of N and 5 pounds of S may replace nutrients lost to defoliation, but check that the crop has a good chance of recovery before investing more into it. Look for new leaves from the growing point or for resumed flowering. This may take a few days to show up after a hail storm. Remember that a crop that does recover from hail will be delayed, and that a nitrogen top up could delay it further. Consider whether the crop still has enough time to mature in a typical season.
Canola recovers from early hail: 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 maturity of the crop can be delayed.