A suspected severe case of clubroot just across the border in Cavalier County, North Dakota is a wake-up call for Manitoba farmers.
“I’m drawing attention to this because it’s at high levels right there so you can probably expect it’s at high levels close by and there is greater risk in those areas (close to the border),” Angela Brackenreed, the Canola Council of Canada’s Manitoba agronomy specialist said in an interview last week.
Thirteen Manitoba fields in 10 rural municipalities have clubroot (Plasmodiophora brassicae), a soil-borne disease, which can decimate canola yields, but mostly at low levels.
Clubroot was discovered in North Dakota last fall. But earlier this month a canola field near the border was discovered to have plants with large clubroot galls, which in pictures looks similar to those found in severely clubroot-infected Alberta fields, Brackenreed said.
“That would indicate those clubroot spores are at a much higher level than we anticipated and it has been around longer than we anticipated,” she said, but added she hasn’t seen the infected field herself.
“This place in North Dakota is very close to the Manitoba border. Manitoba farmers close to the border should be particularly diligent, but as I say, if we look hard enough I assume it’s there in some level in most areas in Manitoba. That’s just an assumption.”
Resistant varieties or not?
That’s why the Canola Council of Canada recommends Manitoba farmers grow clubroot-resistant canola varieties even if they don’t have clubroot. Several varieties are suitable for Manitoba, although seed supplies will vary, Brackenreed said.
Anastasia Kubinec, oilseed specialist with Manitoba Agriculture, Food and Rural Development, agrees farmers need to be vigilant, especially in areas where clubroot has been detected. But Kubinec advises farmers not to grow resistant varieties until their fields have tested positive to avoid a breakdown in genetic resistance.
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“I think farmers should test their soils to see whether or not they have clubroot,” Kubinec said. “If they do then use those clubroot-resistant varieties. They shouldn’t use that tool when they don’t need it because then they may lose that tool and not have access to it when they have a real severe case.”
Ultimately it’s up to the farmer, she added.
Brackenreed said if a field doesn’t have clubroot then growing a clubroot-resistant variety is not at risk of breaking down because it isn’t exposed to the pathogen. And if there are low levels of clubroot present the variety will resist infection.
“Grow it before you even think you have clubroot there at all and you reduce your risk of getting it,” she said. “What we’ve seen in Alberta is really no action was taken until things got quite severe… and now we are dealing with the breakdown of clubroot resistance. We can greatly reduce the breakdown of clubroot resistance if we grow those varieties when there is a very low spore population there.”
Both agree the best protection is discovering it early before it’s widespread in a field and spore levels are relatively low.
In addition to growing resistant varieties after the disease is found, farmers should clean equipment before moving to other fields and grow canola less often in their rotation — ideally one year out of four. But even a two-year break will help, Kubinec said. Many farmers still grow canola every other year in the same field.
“If you grow a clubroot-resistant variety and grow wheat-canola, wheat-canola and think you’re never going to get clubroot, it’s a dream,” Kubinec said.
Lengthening canola in the rotation will also reduce yield losses due to other pests, including blackleg, a fungal disease, which this year will rob more canola yield than clubroot in Manitoba, she said.
Some have clubroot but the symptoms aren’t visible yet. That’s why soil testing is recommended.
“We have been doing this canola disease survey for six years,” Kubinec said. “We have only found one field that had severe infection and it was in a very small portion of the field. We have surveyed every RM but not every field in every RM, but we do look at different fields every year too. So I think between the soil sampling and surveying we do, and if farmers start surveying, we will find more (infected) fields.”
Clubroot-infected canola will appear to be ripening prematurely. But other diseases such as blackleg and sclerotinia can cause that too.
Clubroot was first discovered to be damaging canola crops in the Edmonton area about 10 years ago and has since spread to thousands of fields, advancing by about 25 kilometres a year.
Clubroot spores can persist in the soil for 20 years.
In 2012 clubroot DNA was confirmed in two Manitoba fields sampled in 2011.
MAFRD reported in 2013 plants from two unrelated fields showed symptoms of clubroot galls on their roots and tested positive for clubroot DNA.