Canola School: Manage blackleg well to manage verticillium better

(Justine Cornelson/Canola Council of Canada)

Verticillium stripe — a disease first discovered in Western Canada in 2014 — appears to be taking advantage of the stress to canola plants caused by an old, familiar disease pathogen.

While research to understand Verticillium longisporum in the Prairies is still in its early stages, there’s a hypothesis that its prevalence in a canola field could be linked with earlier infection from blackleg.

The combination of the two diseases may have been to blame for some disappointing yields in 2022, explains Chris Manchur, agronomy specialist with the Canola Council of Canada.

“The crop looked good, but then when it came to the weigh wagon, five to 10 bushels were missing. So likely, the culprit could have been that verticillium and blackleg,” he says, in this new Canola School episode, filmed near Winnipeg, Man.

(source: Canola Council of Canada)

While blackleg prefers wet conditions and infects plants from the leaves down, verticillium is a soil-borne pathogen that starts in the roots and thrives in hot, dry conditions, interfering with plant and nutrient uptake. Both can be diagnosed by examining plant stems — blackleg causes its signature black wedges when looking at a stem cross-section clipped at ground level, while verticillium leaves a grey-ish starburst pattern, with characteristic black dots or microsclerotia striping underneath the outer layer of the stem.

Since there are no fungicides registered for verticillium in Canada, the best way to manage it is to manage other canola stressors, including blackleg, says Manchur.

“We have to think of that canola plant and its overall plant health. Here in Manitoba, we had a lot of excess moisture, we had flea beetle feeding, and then we also had blackleg, which really favours some of those conditions. So if the canola plant is actually trying to mount a defense against those, then we’re going to see its ability to defend against other pathogens be reduced,” says Manchur. “That’s when verticillium may have that opportunity to strike.”

Selecting varieties with appropriate blackleg resistance — based on race testing samples from the field, ideally — should help minimize that opportunity for verticillium, he says.

Dr. Dilantha Fernando at the University of Manitoba has been working on comparing susceptibility to verticillium in existing canola germplasm submitted by seed companies. Manchur says growers should expect to see more information on how different canola varieties respond to verticillium in the future.

Check out this Canola School episode for more on what’s known about the one-two punch from blackleg and verticillium, with Chris Manchur:

Related: Go early or not at all on blackleg control

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