Canola growers get grim warning on clubroot threat

No varieties have strong resistance to new pathotypes, longer rotations are ‘the best management option left’

Alberta clubroot map 2014
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The Alberta Canola Producers Commission is urging producers to step up their efforts to contain clubroot in the province.

“Since new data indicates some forms of clubroot resistance are no longer functioning well against new clubroot pathotypes in some of the heavily infested fields, we encourage you to consider a comprehensive management plan that includes all of these aspects of clubroot management on your farm,” the commission said in a news release.

The news release contains an article from the April 2 issue of Canola Watch newsletter that states “the best management option left” is a four-year rotation as “no current varieties have strong resistance to (new clubroot) pathotypes.”

“If growers have used resistant canola two or three times already on fields that were moderately to highly infested with clubroot, these fields are at high risk for having one or more of the different pathotypes,” says the Canola Council of Canada newsletter. “Resistance breakdown is a numbers game, and with the number of spores a serious clubroot patch contributes to the soil, most bets would be placed on clubroot’s ability to adapt. Longer rotation is necessary to slow the pathogen shift that is occurring in these fields.”

It notes University of Alberta plant pathologist Stephen Strelkov tested soil samples from 27 fields in Alberta that were seeded to resistant varieties in 2014 and experienced higher-than-expected levels of gall formation.

“Of those 27 fields, 16 have clubroot pathotypes that suggest the clubroot population in those fields had shifted to overcome the resistance trait in the variety grown,” the newsletter says.

“These fields are at very high risk of developing high spore loads of a new pathotype that current resistance won’t control. The patches currently range from 10 acres to a few square feet, but can spread quickly without immediate rotation action, reduced tillage, and equipment sanitation. Even with a four-year break, these fields could still be at risk of increasing spore loads leading to an economic level of infection. What the four-year break provides, in the case of these fields with the new pathotypes and those with heavy spore loads, is time for a solution to come forward — hopefully.”

Growers in areas known to have clubroot should scout closely for clubroot when using resistant varieties; avoid tillage; and control canola volunteers and weeds that can host clubroot.

The newsletter also makes a renewed pitch for cleaning equipment before moving to another field.

“Few growers are taking time to disinfect (final misting with bleach, EcoClear, or HyperOx) equipment because of the time it takes. But growers in these higher-risk zones must at least knock the dirt off equipment before leaving fields. At least 90 per cent of clubroot spores that move from field to field can be stopped by scraping off dirt.”

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