Survey shows 36 counties and municipalities have found 383 new infected fields
Four new Alberta municipalities reported clubroot for the first time last year, bringing the total to 28 with confirmed cases of the disease.
The new municipalities are the Municipal District of Lesser Slave River and the counties of Clearwater, Smoky Lake and St. Paul.
It’s a sign that clubroot is continuing to spread across Alberta from its epicentre near Edmonton, said University of Alberta plant pathologist Steven Strelkov.
A 2014 survey of 36 counties and municipalities found 383 new clubroot-infested fields, which brought the total of number fields confirmed to have clubroot to 1,868 since the survey began in 2003.
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It is the second largest single-year increase in the number of new cases since the survey began.
The severity of clubroot infestation ranged from mild to severe.
All cases of severe clubroot were found in susceptible canola varieties or varieties of unknown resistance.
Of the 35 fields confirmed to be resistant hybrids, 12 had no symptoms of clubroot and 17 were very mild cases.
“It’s not surprising we found it in the fields, and it will not be surprising if more turns up,” said Strelkov.
In 2013, clubroot was found in a field of a resistant variety.
Strelkov said researchers tested samples from the infected field on all resistant canola varieties and found that the new strain was able to overcome resistance in most of the clubroot resistant varieties.
“Unfortunately, everything we tried it on, we could break down the resistance. It has overcome resistance to all the cultivars,” he said.
Pathogens found on six resistant cultivars last year will be tested in the greenhouse for virulence patterns.
Strelkov said discovery of more strains of clubroot overcoming resistant varieties is a worrying trend and cautions farmers not to grow resistant varieties in close rotation in heavily infested fields.
“Try to move to a healthier rotation,” he said.
Clubroot remains uncommon in southern Alberta, despite its increasing prevalence. Except for three unconfirmed reports of the disease in the County of Newell near Brooks, no other new clubroot infestations were identified south of the counties of Red Deer and Stettler last year.
The sole confirmed clubroot infestation in Cypress County was identified in 2009, just inside the city limits of Medicine Hat.
The disease was also discovered in the town of Stettler in 2013.
mary.macarthur@producer.com
