Beware of blackleg

It's an unfortunate fact that diseases can mutate and evolve to overcome genetic resistance. What's more unfortunate is that tightening up canola rotations can speed that evolution. Recently, new strains of blackleg have been showing up in canola — strains that are unaffected by current genetic resistance. While plant breeders are hard at work developing new resistant varieties, the Canola Council of Canada is reminding farmers about several things they can do to combat the disease and preserve what genetic resistance we do have now.

Agronomists, plant pathologists and this editor will tell you that the first step in controlling blackleg is keeping canola to a one-in-four year rotation. But if everyone did that, we likely wouldn't be having this discussion, so let's move on to other steps you can take to manage blackleg, according to the Council's latest release on the topic.

1. Choose a variety with an MR or R rating for the disease. The tighter the rotation, the more important the R rating.
2. Rotate varieties. This works because different lines carry different sources of resistance, according to the Council's release.
3. Scout early for signs of the disease and again just prior to maturity. Cankers or lesions that form at the base of the plant are responsible for significant yield loss.
4. Control volunteers in the years in between canola crops. This includes any host crop, such as wild mustard. Volunteers act as host to the disease, setting back any advantage to rotating away from canola.
5. Use certified seed to ensure genetic uniformity
6. Fungicide acts as protectant only, and must be sprayed in anticipation of the disease, not after infection is wide-spread. According to the Canola Council, research at AAFC Melfort found fungicide use made the most difference on those varieties with a less than R rating.

In addition to all this, remember to keep growing conditions in mind. Warm and wet weather can speed along development of the disease. And because blackleg spreads by wind, it's important to scout the field margins between last year's and this year's canola field (if growing side by side). The Canola Council also says that burning stubble is not effective control — the thick base of stalks which carries so much inoculum rarely burn completely.