LETHBRIDGE — It pays to spray for sclerotinia when the crops are better than average and when the conditions are right.
Central to this is the presence of the disease’s inoculums and high humidity levels. Both are present in most areas of Western Canada this year.
“You need moisture ahead of bolting and then damp soils as the plants go into bolting,” said Murray Hartman of Alberta Agriculture.
“It doesn’t have to rain to cause problems. High humidity of 75 percent or so will do it.”
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The tiny mushroom apothecia develops from a cagy sclerote that comes alive only when exposed to wet soils.
As well, it waits until it is shaded by the crop’s canopy before developing a new wave of spores capable of infecting the canola.
The canola leaves provide the necessary cover from daytime heat and wind so that the fungal bodies can go to work. This coincides with flowering’s start.
Staging of plants are highly variable across the West this year, with plants from four leaf to 50 percent flower, so spraying strategies can still benefit most producers’ fields, said Ed Thiessen of Syngenta.
“In areas that have seen the disease before, there is a real risk of it being there this year,” he said. “Conditions are about as favourable as it gets.”
Spraying is most effective between 20 and 50 percent flower, said Russell Trisha of BASF.
Hartman said it’s not difficult justifying spraying this year.
“You only need a 25 or 30 bushel crop to warrant going with an application this year due to the high prices,” said Hartman.
Thiessen said many seed growers have adopted split applications of fungicide to ensure they avoid large losses and get a cleaner crop.
“(I can see) in the future, with the high yielding hybrids and prices we are getting now, it is worth protecting … for many growers by moving to split applications ,” he said.
Some of the most recent canola hybrids are sclerotinia resistant, but while that reduces the chance of serious wreck, it doesn’t eliminate losses during years when disease pressure is at it heaviest.
Kristin Hacault of Pioneer Hi-Bred said it makes sense to spray higher potential canola crops, depending on the sclerotinia threat, field conditions and whether sclerotinia is known to be present.
Thiessen said growers need to evaluate their fields, particularly areas that have highly variable development, and aim to spray when there is moisture under the canopy and flowering is underway for the largest group of plants in the at-risk flowering stage.
“And not just when you can get an aerial applicator,” he said.
Hacault said resistant genetics add flexibility to the timing.
Some growers are applying a herbicide and a fungicide in a tank mix, but Thiessen said this can cause problems in the sprayer tank.
“Try to make sure that if you’re loading up the tank with herbicide, fungicide, micronutrients and other stuff that you aren’t adding to the stress of an already stressed crop or yours by gumming up the sprayer.”
