Analysis of weather, microclimate, and canopy density on Sclerotinia stem rot disease in canola

Abstract

Sclerotinia stem rot disease (SSR) in an increasingly important disease in the Canadian prairies creating unpredictable yield losses ranging between 5 and 100 percent in Manitoba. Management is extremely important due to the little commercially available resistant canola varieties. Caused by the fungus Sclerotinia sclerotiorum, sclerotinia begins its life cycle as sclerotia in the soil. Under specific environmental conditions sclerotia germinates and eventually releases ascospores into the surrounding atmosphere. Ascospores land on senescing flower tissue of the canola plant and subsequently land on the leaves and stems and begin to kill the entire plant. Canopy density and weather are important factors known to influence disease incidence of SSR as they are capable of modifying the microclimate and creating various environments that affect all levels of the disease cycle. Several researchers have proven that moderate temperatures and moisture is required for sclerotia germination, increasing temperatures and decreasing relative humidity is required for day time release of ascospores and moisture and humidity is required within the canopy for spore germination on petals and for further infection. This study attempts to validate these findings and more accurately depict the specific environmental conditions, and canopy densities most favourable to disease development and incidence. By understanding the environmental requirement for SSR, cost effective management strategies can be implemented based on the findings obtained within this study. More importantly, weather can be used as an indicator of risk in canola crops in Manitoba which can be used to determine appropriate fungicide application rates and timing.