Prevention best weapon against sclerotinia

Weather related | Canola is susceptible to the disease if it receives moisture during the flowering period

There were several reasons for disappointing canola yields across Western Canada this year, and sclerotinia was one of them.

The fungal disease, which thrives in hot and moist conditions, robbed farmers of 10 percent of their yield in Alberta and Saskatchewan and five percent in Manitoba.

Clint Jurke, an agronomy specialist with the Canola Council of Canada, said the rule of thumb for yield loss due to sclerotinia is to halve the incidence.

That means 20 percent of Alberta and Saskatchewan crops and 10 percent of Manitoba crops suffered from the disease this year.

“Sclerotinia was very big, particularly through central and northwest Saskatchewan. It was probably the number one yield robber in that area,” said Jurke.

“Sclerotinia is the one disease that is almost entirely controlled by the weather pattern that you have. Crop rotation, previous crop history, things like that don’t really matter very much with this disease. It’s all about how much moisture you’ve had, particularly around that flowering period.”

Randy Kutcher, former oilseed specialist with Agriculture Canada, recommended using the canola council checklist to determine whether fungicide spraying is worthwhile. The list includes assessments of recent weather, forecast, crop canopy and yield potential.

Scouting at first flower and then using a petal test kit will also give guidance on spraying, but Kutcher said few producers use the kits. 


“Even if you don’t think you have much inoculum in your field, you can still get spores coming in from adjacent fields,” said Kutcher, who now focuses on cereal and flax pathology at the University of Saskatchewan.

“The more growers deal with the disease, the better feel they get for it and the years that it’s going to be a problem.”

Sclerotinia is tricky.

Spraying is unlikely to be effective in preserving yield by the time it is visible in the crop. Prevention is the main weapon in farmers’ arsenal.

Kutcher said his best recommendation is to scout at swathing time to gather information on potential load in the soil. The data can be useful the following year if weather conditions favour the disease.

“Get off the swather, three or four or five places in a quarter section, and figure out how much sclerotinia (you) have. It’s a pretty easy disease to recognize.”

Alberta Agriculture oilseed specialist Murray Hartman said some canola varieties are tolerant to scler-otinia but they work best when disease pressure is low. Even then, fungicide spraying will likely be required if conditions favour the disease.


“I would say there hasn’t been a high uptake on those varieties,” said Hartman.

Abundant sclerotinia in one crop year is not a guide to conditions in the following year because of the disease’s weather dependence. 

However, Hartman said the disease’s apothecia bodies can remain in the soil for three or four years and cause problems when conditions are right. 

That’s why crop rotation is not a huge factor in control, agreed Jurke. Sclerotinia is not particular about its host.

“Any dicot plant is a host for this disease, so it doesn’t matter if you’re growing canola or you’re growing peas or you’re growing lentils or you’re growing even alfalfa or Can-ada thistle. They all will produce sclerotia.”

The bright side is that there are many effective fungicides.

Sclerotinia has developed resistance to benomyl, the most popular fungicide used in the 1990s, so that is a warning to producers to vary products and modes of action.