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A vivid new video from the Canola Council of Canada zooms in on blackleg, showing how the canola disease infects a plant, how it spreads throughout a field, and what growers can do to protect blackleg resistance traits. The video, called “Blackleg Disease and Resistance Management,” is posted at www.youtube.com/canolacouncil.
The video explains how growing varieties with the same type of resistance in a short rotation increases the selection pressure for blackleg races that can overcome specific resistance genes. Rotation away from canola for two or three years is the best way to support genetic resistance in fields where management practices could have selected for virulent blackleg races.
The video arms growers and agronomists with the understanding of the blackleg disease cycle and encourages assessing the level of blackleg in this year’s canola. Pre-harvest scouting is an important step.
To scout, visit canola fields in the week or two before swathing or straight cutting. Pull up a few random plants and clip the stem just below ground level. Look for black discolouration of the cross section. A rating of “0” means no blackleg stem discolouration. A rating of “5” means the stem is completely discoloured and blackleg has killed the plant. A wedge of black that covers 26-50% of the cross section is considered a “2” on the severity scale.
Repeat this at a few sites within the field. If average severity is 1.5 or more, blackleg races in that field are likely starting to overcome the genetic resistance in that particular variety. Rotating varieties to bring a mix of blackleg resistance genes to the field over time can help prevent or delay the breakdown of resistance.
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