Managing Blackleg and White Mold in Canola


In the U.S., blackleg and white mold are two of the most challenging diseases in canola production. Below find some tips for dealing with both of these diseases.

  • Blackleg is a fungal disease. Spores can infect a crop that's exposed to rain early in the growing season. If it's too dry early in the growing season, growers usually won't see much blackleg pressure.
  • Damage from hail and/or insects can allow the fungus to invade young plants.
  • Canola is most vulnerable to yield loss if the spores infect plants before the six-leaf stage. Once plants get to the 8- to10-leaf stages, less impact on yield is seen.
  • Leaf infection is not directly damaging to plants, but as infection moves to the stem, severe cankers can develop.
  • If the plant develops a stem canker due to blackleg infection, hot weather can cause severe harm by further restricting water and nutrient availability.

New Races Threaten

Until recently, planting resistant varieties or hybrids provided reasonable protection. However, new races of the disease have appeared. According to Dave Charne, Pioneer research director for canola, some of the traditional sources of resistance aren't as effective against these new races.

Pioneer screens new hybrids in disease nurseries, exposing them to the predominant local strains of blackleg. This provides a good indication of how these potential hybrids will fare in the real world. Pioneer uses two forms of resistance to protect canola hybrids. The non race-specific resistance provides adequate protection to the disease regardless of the races present. While it doesn't prevent leaf infection, it reduces the amount of damage at the stem level.

Pioneer also is adding new and unique forms of resistance to provide race-specific resistance that can stop leaf infections from developing. While it can be more complex to combine these two forms of resistance, race-specific resistance is valuable. The best protection comes from combining both types of blackleg resistance into a hybrid.

White Mold

White mold, or sclerotinia, is a difficult disease to control in canola production. It can survive in the field for many years under certain conditions. Because it has a wide range of host plants, crop rotation isn't an easy solution.

A long rotation to keep susceptible plants out of the field for several years is not a practical option for most producers.

The disease thrives in lush, heavy and humid canopies. It also does well in soils with plenty of nitrogen. Growers may want to consider hybrids that resist lodging to avoid plant-to-plant spread of sclerotinia. Generally, thinner canopies with plenty of air movement help thwart white mold. That's why it's important not to exceed plant population recommendations.


The only options to control white mold historically have been long rotations and fungicides, notes Charne. However, Pioneer is offering a resistance trait that reduces the impact of white mold by 50 percent.

This in-the-bag resistance provides flexibility for growers who can't always get into the field to spray when they need to. Charne notes Pioneer has better products with higher levels of resistance in the research pipeline.