The Canola Council of Canada (CCC) has researched sclerotinia stem rot that occurs due to moisture and has concluded that this dilemma facing growers leads them to hold off on using spray.
The CCC reports that dealing with lower rainfall this year must consider conditions as they change flowering.
"Given the low moisture situation and lower canola yield potential in many areas of the prairies, growers wonder if they need to spray fungicide to manage sclerotinia stem rot," CCC vice president of crop production and innovation Curtis Rempel said. "It may be more of a last-minute decision this year, requiring close attention to the risk during early flowering when fungicides are applied."
Even, if rainfall is below normal, moist soils and a humid canopy can lead to infection. Even if soil has become dry under a thin canopy, rains at the start of flowering will get the apothecia germinating and plants filling in.
"A few mid-season rains can completely change the risk forecast," Rempel said.
Frost, flea beetles and other stresses on stand establishment affect canola fields throughout a variety of stages. Some plants are flowering, some are just coming into bud and some are still at the five-leaf stage. This renders difficulty in determining when to make a fungicide application.
"Assess a few small areas and look at 100 plants in each. Base fungicide timing on the group that represents the highest proportion of plants across the field," Rempel said. "If half are flowering and half are just budding, this might be a situation for a split application -- if conditions are right for disease development."
Sclerotinia stem rot remains the most widespread and expensive disease for canola growers across Canadian prairies. It causes significant yield loss in any region, and growers often factor spray costs into their budgets rather than trying to guess when yield loss might occur.
"Many growers will second-guess whether to spray fungicide this year. Growers in this situation may want to leave a few check strips in each sprayed field," Rempel said. "Mark those strips, take them to yield and compare results to the sprayed results. This will help with future decision-making in similar conditions."
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