So far relatively low levels of sclerotinia infection are being reported in most areas. Blackleg is appearing in eastern Manitoba and southern Alberta.
Scouting and identifying disease(s) present can be a valuable tool for assessing this year’s production practices and preparing for next years. Here’s what to look for with blackleg: symptoms showing up at this stage of the season are greyish lesions on the stem with the black picnidia spots, and also basal lesions (cankers) — which are the most serious. Basal lesions can’t really be properly identified until you cut through the base of the stem and look for blackened infection. This infection will eventually grow through the stem, cutting off nutrient flow. If you see plants drying up, cut a few open at the base of the stem with clippers to check. With sclerotinia look for white lesions or fuzzy rot on the main stem or on branches. Sometimes the plant may look healthy at the base, but there will be dead branches. Infected stems and branches will have white-grey tissue (not green) and will often start to shred apart easily. Click here for more information and photos to help with identification.
If sclerotinia is present, assess the % of infected plants since half of this number will give a yield loss estimate. If fungicide was applied, evaluate that decision. Was a check strip used to determine if the disease was at least suppressed? Is it obvious infection occurred late in the flowering period, suggesting a later or split application may have been more effective? Was a fungicide not applied and perhaps should be under similar conditions in the future?
If a high incidence (anything greater than 15% of plants) of blackleg is found, then this field should not be used in a tight rotation – consider rotations of one in three or one in four years. Also, the next time canola is planted on this field, ensure it is not the same variety, especially in tight rotations.