Producers usually scout canola fields for sclerotinia in late June or early July, when the crop starts to bloom.
But scouting later in the year, when the crop is being swathed, can also yield valuable information that might save thousands of dollars down the road.
Randy Kutcher, a plant pathologist with the Crop Development Centre in Saskatoon, said at a recent field day at Agriculture Canada’s Melfort Research Farm that deciding whether to spray canola for sclerotinia can be frustrating and expensive.
Maintaining records of past infections can remove a lot of the guesswork.
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According to Kutcher, producers should spend an extra 15 minutes in each field during swathing, to assess sclerotinia infection and make notes for future reference, he said.
“I think you’ll be much better off, getting off the swather at maybe five places in a quarter section, maybe more if you can, pulling out 10, 15, 20 plants at each (stop) and counting how many have sclerotinia,” Kutcher said.
“If you do that for five years on most of your fields, you’ll have a much better feel for (whether you) have sclerotinia … and how significant (it) was.”
Canola growers normally base their fungicide application decisions on several factors.
Market prices influence the decision, as do application costs, precipitation immediately before and during the crop’s early flowering stage, field conditions, yield potential and risk of infection.
The last factor, risk of infection, is often the hardest to assess. Determining the risk begins with an assessment of whether disease inoculum is present in the crop.
Locating tiny sclerotia bodies in the soil is next to impossible. The bodies are black and roughly the size of a mouse turd. It’s easier to locate apothecia, the small tan-coloured mushroom-like structures that produce infectious sclerotinia spores.
The apothecia are shaped like miniature golf tees and their heads are usually smaller than the head of a two-inch nail.
Presence of apothecia is a good indication that spores are present.
Petal tests are another effective assessment tool.
Petal test kits can be acquired from Discovery Seed Labs in Saskatoon and should be used when canola crops are in the 15 to 20 percent flowering stage, said Bruce Carriere, president at Discovery Seed Labs.
A field’s past infection history is another critical factor in determining infection risk.
Fields that had heavy infection rates in the past are more likely to require fungicide treatments.
Conditions appeared to be ideal this year for the development of sclerotinia but in many areas, the disease did not emerge as expected.
In some cases, recurring and abundant rainfall may have inhibited growth of apothecia, Kutcher said.
In other cases, heavy rain may have washed fallen petals off the canola stems, he said.
