Yield loss from hail will depend on crop stage and severity of the damage. In addition to physical injury, hail damage allows a point of entry for diseases such as alternaria black spot and blackleg to infect canola plants.
Many people wonder about applying crop enhancement products such as fertilizer and micronutrient blends or fungicides on hail-damaged crops. There is little data available on the efficacy of such products under these extreme conditions, so if trying them leave appropriate check strips in order to make an accurate yield comparison at harvest. Fungicides may help reduce the development of diseases but make sure the remaining yield potential warrants protection and conditions remain conducive to disease development. Also consider the possible impact of delayed maturity, as fall frost damage could negate the potential benefits of the fungicide application.
To estimate yield loss, click here and scroll down to Table 7.