An extra year off can make all the difference in managing diseases in canola, according to a recent study by Manitoba Agriculture.
Debbie McLaren, an integrated pest management specialist with Manitoba Agriculture’s soils and crops branch, said results from the first year of a canola crop rotation study show the incidence of disease in canola drops as rotation is increased.
The study, funded by the Manitoba Canola Growers’ Association, was conducted to examine the relationship between crop rotation and integrated pest management.
Both sclerotinia and blackleg, canola’s worst disease enemies, were most prevalent in a two-year rotation, McLaren told producers during a seminar at Ag Days in Brandon.
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“We’re seeing as you lengthen the rotation out of canola, you will have less disease and that was probably the most significant finding.”
Diseases in canola can be managed most effectively in a four-year rotation, she said.
McLaren said most producers know there is a link, but they have to balance the risk with the benefits of today’s high canola prices.
“I think producers are aware but with canola they’re under increasing economic pressure to shorten their rotations,” she said in an interview following the seminar.
McLaren said sclerotinia turned up in 80 percent of the fields studied.
And any field that was infected 20 percent could see yield losses up to 10 percent, she said.
Both virulent and avirulent blackleg were present in fields, she said. The more aggressive virulent strain has been in Manitoba since 1984 and can result in losses of more than 50 percent.
The study used samples from 183 fields across Manitoba, or about 40 fields from each soil region.
Researchers sampled 100 plants from each field to examine for insects and disease.
Of the 100 plants, 30 were cut, washed and prepared for storage to be sent to an entomologist and examined for root maggots.
Once a disease has set in, McLaren advised producers to factor in environmental factors before making a management decision, including monitoring soil conditions, moisture level and using sclerotinia risk mapping available from Manitoba Agriculture.
“Hopefully by using all these measures you are decreasing your risk of disease and you might not have it as often, but there’s a lot of sclerotia out there in the soils so you have to be careful,” she said, adding blackleg spores can survive for several years in the soil.
The study will continue this year.
