Blackleg disease, caused by the pathogen Leptosphaeria maculans, is common in canola across the Prairies. It can cause very high yield loss in cultivars susceptible to the predominant blackleg races in a field. While high yield loss is rare on the Prairies, mostly because farms grow resistant cultivars, blackleg levels are increasing due to shifts in blackleg races and tighter canola rotations. Canola growers can keep blackleg levels low with the following management steps.
The 6 basics
Check canola stems before or during harvest to assess blackleg infection levels. Use the blackleg calculator to assess yield and economic loss associated with blackleg. If economic loss exceeds an acceptable level, move to the next steps. This guide has scouting tips.
Test for blackleg races
Various labs will test stem pieces for blackleg and can provide analysis of blackleg races present. These results will help growers choose the best canola R-genes to use the next time canola goes on that field.
Choose resistant cultivars
This is the most effective management step. Genetic resistance is the reason blackleg is, for the most part, well managed in Canada. When blackleg pathogen levels increase and race populations shift within a field, growers have the option to choose cultivars with resistance to the specific blackleg races in a field. List of cultivars with R-genes identified. Watch the how-to video at the bottom of this article.
Extend the break between canola crops
A break of two or more years between canola crops on the same field will give most blackleg resting spores time to degrade, greatly reducing the risk. When canola is grown back to back or with a one year break, blackleg risk escalates considerably. In tight rotations, scouting is essential and it becomes more important to use cultivars with genetic resistance to the most common blackleg races in a field. Seed treatment will also reduce the risk.
Ask for enhanced seed treatment
Recent research shows that cotyledon infection results in higher disease incidence and severity at canola maturity. Certain advanced seed treatments can protect seedlings from early infection. See Table 1 here for seed treatments that work on blackleg. Ask your seed provider which seed treatments they recommend. Agriculture and Agri-Food Canada research shows that seed treatment provides an economic benefit only when used on susceptible cultivars. Resistant cultivars see no benefit from seed treatment because their blackleg severity levels are very low.
Apply foliar fungicide
A number of foliar fungicides can protect canola from blackleg. See Table 2 here for foliar fungicides that work on blackleg. Fungicide needs to be applied before infection, and economic benefit, if it is to occur, will come from early applications at the one- to two-leaf stage of the crop. Like seed treatments, economic benefit occurs only when used on susceptible cultivars.
Verticillium stripe bonus. Researchers have shown a connection between blackleg severity and verticillium stripe severity. One way to reduce verticillium risk is with a strong blackleg resistant cultivar.