WINNIPEG – While sun bathers may have been looking for warmer weather the past couple of weeks, the fungus that causes stem rot on canola has been basking in the cool, moist conditions.
The same weather has sent farmers to their fields in droves to spray for sclerotinia, according to provincial agriculture departments.
“An awful lot (of fungicide) has gone down by air and by ground equipment,” said Ieuan Evans, a research scientist with Alberta Agriculture.
Evans said conditions are good to ideal for sclerotinia outbreaks in 90 percent of canola-growing areas, which stretch from north of Calgary and east of Stettler.
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Model-based estimates used by Statistics Canada showed the 2025/26 crop year has seen increases in canola, corn for grain, oats and lentils production while seeing dips in spring wheat, durum wheat, soybeans and barley in comparison to 2024/25.
Farmers near Grande Prairie and Fahler in the northern Peace River district have also been spraying, he said.
Farmers in Manitoba and Saskatchewan have sprayed about one million acres, estimated Gary Platford, a plant pathologist with Manitoba Agriculture.
“Some of the growers are just sort of doing it routinely, much in the way you’d buy insurance,” he said.
In severe years, Platford said some growers have experienced 30 percent yield loss from the disease. In average years, they lose about five percent.
Platford has been putting out a sclerotinia forecast every three days for the two provinces based on Environment Canada data.
He said much of the canola-growing area in Manitoba and eastern Saskatchewan is highly susceptible, except for parts of southwestern Manitoba. Southern and parts of northwestern Saskatchewan have a low to moderate risk of a disease outbreak, he said.
Risks vary
Platford said risks within an area may vary, depending on crop rotation, the history of the field, and whether adjacent fields have ever been infected.
To germinate, sclerotinia spores need about 10 days of moist surface soil and temperatures in the range of 20-25 C.
Evans said producers need to spray when the fields are “at their yellowest” to hit the maximum number of petals.
“They (the petals) are the tinder that gets infected with the fungus,” Evans said. “Without the fungus, the disease can’t get going.”
Platford said farmers can confirm whether the fungus is present with a culture or chemical test. Because of the late start this spring, agrologists said spraying was also delayed.
During hot, dry weather farmers typically have two to three days where fields are at the right blossom stage, Evans said. This year, they’ve had as much as a week.
Platford said about 20 percent of the fields in northwestern Manitoba and northeastern Saskatchewan are still at the right stage for spraying.
Alberta Agriculture distributes a fact sheet which helps farmers make their own predictions about the likelihood of infection in their fields.
