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June surface soil moisture conditions indicate that much of the Prairie canola growing region currently has sufficient soil moisture to support germination of Sclerotinia sclerotiorum sclerotia (Fig. 1). Cumulative rainfall from May 30 – June 28 was the highest in the Edmonton, Lethbridge, Winnipeg areas, and lowest in northern Saskatchewan and the Peace River area of Alberta (Fig. 2). When rainfall over the whole growing season (April 1 – June 28) was considered, the Edmonton area was much higher than average (Fig. 3). Recent heavy rains across the Prairies have significantly increased these amounts. Temperature over the May 30 – June 28 period was highest in southern Manitoba and eastern Saskatchewan and lowest in western Alberta (Fig. 4). For the whole growing season temperatures have been approximately normal, except in eastern Saskatchewan where they have been below normal (Fig. 5). Where temperatures remain moderate (10–20°C) these high moisture conditions will promote the germination of S. sclerotiorum sclerotia and raise the risk for Sclerotinia stem rot. If these conditions persist, apothecia development andascospore release are expected to continue in many areas.
Many canola fields have now reached or passed 50% flowering, reducing the window for fungicide application. Growers with crops still within the recommended application window should continue to monitor local rainfall, canopy humidity, and field conditions, particularly in fields with a history of stem rot or dense crop canopies. While regional soil moisture maps indicate favourable conditions for pathogen development, localized rainfall and field-specific canopy moisture remain the key drivers of infection risk and should be considered when making fungicide decisions.
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