Weather, Microclimate, Canopy Density and Neighbouring Non-Host Crop Impacts on Sclerotinia Stem Rot Disease in Canola
Pernerowski, Reanne Jr
Sclerotinia stem rot (SSR) disease is one of the most devastating diseases of canola in the Canadian prairies caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary. Yield losses ranging between 5 to 100 percent can be experienced as a result of this disease. This study evaluated the impacts of weather and microclimate on SSR development in canola with varying canopy density. Ascospore dispersal and disease incidence were compared under modified canopy densities and misting regimes to alter microclimate. The effectiveness of crop rotation and the influence of neighbouring non host crops were also analyzed in this study. A randomized complete block design was used to compare values for canopy density, microclimate and disease development under 3 seeding rates and 3 fertilizer treatments. This design was implemented over 4 site-years, in Winnipeg and Carman during 2011 and 2012. Weather stations were installed to monitor environmental conditions at each site and compare these to disease. At each site, a wheat plot was created to examine ascospore release under a non-host crop to determine the influence such a crop may have on neighbouring canola fields. Results of this study showed that peaks in ascospore concentrations occurred simultaneously between Winnipeg and Carman fields during both years indicating that regional weather conditions are important for ascospore release. Disease development in canola fields occurred where adequate precipitation and relative humidity were present prior to ascospore release and dispersal. A decrease in relative humidity and an increase in temperature were required for spore release from apothecia. Disease development was greater in Carman, where relative humidity values overall were higher and temperatures remained lower compared to those in Winnipeg in 2011 and 2012. Ascospore release did occur under the wheat canopy and ascospores were dispersed to a distance of at least 7 meters from the plot.