The decision whether to spray a fungicide for sclerotinia stem rot always comes back to the disease triangle — a susceptible host, the presence of the pathogen, and a favourable environment — and many canola-growing areas currently have all three.
Under “favourable environment,” sclerotinia requires moist soil conditions to germinate. The last few years have been dry in much of Western Canada, but that does not mean the pathogen is not present. In fact, it could lead to a flush of spore-producing apothecia germinating, says Chris Manchur, agronomy specialist and sclerotinia lead with the Canola Council of Canada, in this Canola School episode.
“The presence of the pathogen in the soil is as sclerotia. They’re melanized, with kind of a hard, rind-like coating that unless you receive a lot of moisture usually won’t germinate. So even though we’ve had some very dry years, that sclerotia can still be present in your fields. And if it’s still present, and then we get a moist year, you could see that flush of germination happening from that,” he explains. (continues below)
The Canola Council’s Chris Manchur discusses the decision whether to spray a fungicide, the impact of drought on sclerotinia risk, how canola variety might factor into the decision, as well as the Canola Council’s decision tool that’s undergoing beta-testing in this Canola School video:
In addition to the weather itself, it’s important to consider the microclimate within the crop, especially when there’s a lush, dense canopy.
“Just walking through and having wet pants is usually a great indicator that the opportunity for that apothecia to actually germinate and spread spores is at its most,” notes Manchur.
A single sclerotia in the soil can produce up to 15 golf tee or mushroom-like apothecia, which will release the spores that infect the crop. (Above photo of apothecia courtesy Canola Council of Canada/SclerotiniaRiskCalculator.com.)
“Make sure that you’re actually getting on the ground throughout your canopy and looking for these little mushroom-like structures. If it’s very common to find your apothecia within your field, then that is a high likelihood that spores are going to be released. If you’re having a more difficult time finding it, then that risk is going to be a lot lower,” he explains.
The Canola Council is currently beta-testing a tool to help farmers and agronomists determine whether they need to apply a fungicide based on an algorithm that considers the range of factors that are conducive for the disease.
“Using that tool, you’ll be able to make your own assessment using the calculations provided whether a fungicide application is warranted or not,” says Manchur. (You can sign up to be a beta-tester at sclerotiniariskcalculator.com.)