The discovery of a new clubroot strain not controlled by traditional resistant canola varieties underscores the need to be proactive in keeping clubroot spore numbers low.
“This is yet another cue for the industry to continue to take this disease seriously and implement clubroot management plans,” said Dan Orchard, agronomy specialist with the Canola Council of Canada. “We still have an opportunity to get ahead of this disease and limit the impact it has on canola producers and the industry.”
The canola council said Manitoba Agriculture’s discovery of a 3A clubroot pathotype in one field in the province’s south-central region “should encourage all canola growers to implement clubroot management strategies, including scouting fields now for symptoms of the disease.”
“Outside of Alberta, very few fields have been found to contain novel pathotypes like this, and this is the first finding in Manitoba,” the council stated in a release.
The symptoms of clubroot are most evident in fall — either during or after harvest — and producers should be actively scouting by pulling roots and looking for galls, it said. And every grower should be working to contain the devastating disease, the council stated.
“All canola producers are encouraged to grow clubroot-resistant varieties, limit the movement of soil, extend rotations to at least a two-year break between canola crops, control canola volunteers and other brassica hosts, and diligently scout.”
The discovery of the 3A clubroot pathogen is significant because it “is able to overcome some first-generation sources of genetic resistance in commercial canola cultivars,” said Manitoba’s agriculture department.
“Varieties that contain resistance specifically to pathotype 3A are limited,” said provincial oilseed specialist Dane Froese. “There are only two varieties that I am aware that claim specific resistance to 3A that are commercially available. There are another three that contain second generation-type resistance meaning… they don’t specify (that they have resistance) to 3A… so you need to take it with a grain of salt if you choose to grow it in a field with that pathogen.”
He also said taking a two-year break is critical.
“The No. 1 recommendation is crop rotation — having at least two different crops between a canola crop,” Froese said. “That’s a one-in-three-year rotation.”
Greenhouse tests show half of clubroot spores in soil die over four to six years, he added. A field with a million spores will drop to 500,000 after four to six years of being canola-free.
“Once you drop below 100,000 (spores) based on those same greenhouse studies we tend to see less infection of plant root material,” Froese said. “That’s the aim — to draw down the spore load so it’s less aggressively affecting plant roots so you might not notice field loss or visual infection.”
A three-year canola rotation also helps control other pests, including blackleg, a fungus disease that can also decimate canola yields.
Alberta has been the epicentre of clubroot on the Prairies, but the same pattern of its spread is starting to occur in Manitoba. The province’s first case was found in 2013 and the next year there were 13 cases (but 11 were based just on soil samples showing spores, with no visible signs of disease). But so far this year, 40 fields with visible clubroot infection have been confirmed in seven Manitoba municipalities, Froese said.
Unlike Alberta, Manitoba has not made clubroot a reportable disease, but it is encouraging farmers who suspect an infection to let it know. Manitoba Agriculture is also encouraging them to do soil tests for clubroot, even if canola crops aren’t showing signs of infection.
“What we really want is proactive clubroot testing,” said Froese. “Once we have galls (on canola plant roots) in the field it’s not as useful because if we can see symptoms we know the spore load is high enough to cause that.”
Along with a three-year rotation and planting clubroot-resistant varieties, growers should control volunteer canola and other host plants, and clean equipment between fields to avoid spreading clubroot spores.
Cleaning equipment takes time, but is worth the effort while clubroot still isn’t widespread in an area, Froese said.
“If the soil is dry… you can remove about 90 per cent of the soil and that removes 90 per cent of the risk from moving infected soil into a non-infected field,” Froese said. “If you use the pressure washer or air gun to clean it off completely, 99 per cent of the problem is removed. The more we can be proactive with sanitation and managing patches — clubroot usually appears as patches in a field — that really does reduce the spread and the risk overall.”