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Clubroot confirmed in Saskatchewan

Plants in two canola fields in north-central Saskatchewan have been confirmed with a notorious soil-borne disease not seen in the province’s crops until now.

“Industry and government personnel” advised the Saskatchewan Canola Development Commission (SaskCanola) on Friday that plants carrying the disease had been found in both fields, chairman Brett Halstead said in a release Tuesday.

“The confirmation of clubroot in Saskatchewan, although extremely unfortunate, is predictable given the nature of the disease and its eastward movement” from Alberta, he said.

The disease’s appearance in plants in Saskatchewan was made even less surprising when soil samples from a random field in the west-central region of the province turned up positive in July 2009. Clubroot symptoms did not appear on any plants in the province at that time.

Because the disease transfers through soil, properly sanitizing equipment used in infected fields is crucial to prevent clubroot from spreading, said Kristin Hacault, agronomy research manager with seed company Pioneer Hi-Bred in Calgary.

Proper crop rotation is also a must, she said. Even for canola growers who have clubroot-resistant genetics in their seed, it’s recommended that infected fields be used for canola only one year in four.

Scouting for the disease is also important, she said, noting infections tend to appear first in fields’ margins, near the approaches where vehicles enter the field, or on the headlands where equipment first contacts the soil.

Above-ground symptoms to watch for in susceptible crops such as canola include wilting, stunting, yellowing and premature ripening.

Clubroot spores can also survive livestock digestion, so growers will want to avoid use of straw, hay, greenfeed, silage or manure from infested or suspect areas.

Severity of infection can also depend on soil moisture, as the microbes can travel on water running within a field, Hacault said, noting farmers with vulnerable crops under irrigation will want to be particularly vigilant with sanitation, rotation and scouting.

Pioneer, she noted, was the first seed company to have a clubroot-resistant canola variety, the hybrid 45H29, which resists several races of the microbe.

Earth tag

Clubroot affects the roots of canola and other cruciferous field crops (mustard, camelina, oilseed radish, broccoli, cabbage et al) and field weeds (stinkweed, shepherd’s purse, wild mustard). Warm soils, high soil moisture and low soil pH favour the spores’ germination, infection and development.

Once the microbe infects a host plant’s roots, it alters hormone balance and speeds up cell division and growth, creating deformed clubroot galls, which reduce the roots’ ability to absorb water.

Infected plants’ roots eventually disintegrate, releasing resting spores into the soil to travel on wind, water erosion, animals or their manure, people’s shoes or clothing, vehicles and their tires, or earth tag on farm or industrial field equipment.

Resting spore numbers can decline over time without a favourable host crop, but a small proportion of resting spores can survive in soil for up to 20 years.

Fungicides are not considered a practical solution against clubroot in canola and no foliar products or seed treatments are yet registered for control of clubroot on canola in Canada. The risk of spread through contaminated seed or plant material is much less than through transporting contaminated soil, but seed with earth tag from infested areas should still be avoided.

Within Canada, clubroot is established mainly in vegetable-producing regions of British Columbia, Quebec, Ontario and Atlantic Canada, and turned up in canola in Quebec in 1997.

Even after several decades of large-scale canola production in Western Canada, the disease did not hit Prairie canola until it showed up in spots near Edmonton in 2003.

— With information from the Saskatchewan Clubroot Initiative. For more on clubroot, growers can visit the Canola Council of Canada’s clubroot website.

Related stories:

Traces of clubroot confirmed in Sask. field, July 22, 2009

Alta. counties aggressively address clubroot, Dec. 13, 2007

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