The more we use blackleg-resistant canola in a rotation, the more we encourage the buildup of blackleg populations that can successfully overcome that resistance trait. The risk is especially high in regions where conditions for disease — early season rain and humidity — are present most years.
Ideally, in areas where blackleg is present, rotations should include at least two or more non-host crops between canola crops. For growers who choose to include canola in the rotation more often, here are a few disease management tips that may help delay resistance breakdown:
- Grow varieties with an “R” or “MR” rating for blackleg.
- Rotate varieties. Blackleg resistance depends on a number of genes. Growers don’t know which varieties have which resistance genes, but rotating varieties will likely bring a mix of resistance genes to the field over time.
- Scout for disease. Look for blackleg early in the season and just prior to crop maturity. If you see damage on small plants, you may be able to prevent the spread with fungicide. Scouting later in the season gives growers an idea of disease presence and severity in their fields, which is useful for future disease management.
- Control volunteers. Canola volunteers and related weed species such as wild mustard can host blackleg and other canola diseases, making non canola years less effective at reducing disease.
- Use certified seed. With certified seed, each canola plant should have the same genes and be equally resistant.
- Consider a fungicide, but recognize they tend to provide a greater benefit on susceptible varieties.
Click here for more detail on these points and others, including results from Saskatchewan studies showing how rotation influences blackleg and how tillage and burning are not usually effective for blackleg management. See the graphs below for blackleg survey results for the past eight years. Incidence is based on an average of all fields, including those with no blackleg. Some individual fields had higher levels.