Bullock: Weather-Based Assessment of Sclerotinia Stem Rot Risk
Date: July 2013
Term: n/a
Status: Completed
Researcher(s): Paul Bullock, University of Manitoba, Winnipeg MB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
In western Canada, Sclerotinia stem rot continues to be a serious disease of canola. Researchers at the University of Manitoba led a two-year study to assess the risk of sclerotinia stem rot disease on canola based on standard weather conditions and the canopy microclimate. The study showed that climate is a major contributor to disease development based on ascospore concentrations and disease incidence. Growers should be aware of the history of disease and inoculum levels in fields nearby. Fungicide applications may be required on susceptible crops located adjacent to fields with disease history. Application timing of fungicides can be facilitated through weather predictions focusing on precipitation and relative humidity.
In western Canada, Sclerotinia stem rot continues to be a serious disease of canola with a large acreage affected again in 2012. Weather and microclimate are important factors for both crop and disease development. Researchers at the University of Manitoba led a two-year study to assess the risk of sclerotinia stem rot disease on canola based on standard weather conditions and the canopy microclimate. Wind borne spores from within the canola field and from neighboring non-host fields were also monitored to evaluate the impact of spore dispersal on disease risk.
A plot study was conducted at two Manitoba sites, Winnipeg and Carman, during 2011 and 2012 growing seasons comparing high, medium and low density canopy treatments using high, medium and low seeding and nitrogen fertilizer rates. At each site in 2011, a duplicate set of replicated plots were established, with one set irrigated to maintain wet canopy conditions and the other rainfed only. In 2012, sites were rainfed only. Total precipitation during the growing seasons was higher in 2012. In 2011, plots were inoculated with sclerotinia disease after seeding. The 2012 plots were inoculated with sclerotinia during plot preparation in the fall of 2011.
Standard weather data was monitored during the growing season including air temperature, relative humidity, wind speed, solar radiation and precipitation. Within the canola canopy, air temperature, relative humidity, soil moisture, soil temperature and leaf wetness were monitored for each separate replicate for each treatment at both study sites and in both years. Ascospore sampling was conducted to monitor the spore dispersal from individual canola plots and adjacent non-host wheat crop strip. Petal sampling was conducted at early and late bloom stages of canola, canopy density, leaf area index (LAI) and disease incidence measured at all plots.
The study results showed that general overall weather conditions clearly play a critical role in the timing of ascospore release in both host and non-host crops. The timing of peaks in ascospore release were almost identical in both host and non-host crops, both misted and unmisted plots as well as at 2 different locations in eastern Manitoba. The study also found that ascospore production was not increased using a misting system to maintain leaf wetness in comparison to non-misted canola. This may have been a result of the wet growing conditions when the misting system was in use.
Comparison of average daily mean ascospore concentrations over the sampling period in misted (dashed lines) and non-misted (solid lines) plots in Winnipeg (grey lines) and Carman (black lines) in A) 2011 and B) 2012.
The study did not find any correlation between average daily temperature or relative humidity values with daily ascospore levels. Major peaks in ascospore concentrations mainly preceded prolonged periods of high relative humidity followed by a sudden decrease in relative humidity, which agrees with other study findings. This study showed very similar canopy air temperature in the high, medium and low density plots, however the low density plots displayed significantly lower relative humidity. Those plots showed no visible trends in disease incidence suggesting that variation in canopy relative humidity alone was not sufficient to create differences in disease levels. Wind direction played a slight role in the movement of spores away from an inoculated source.
The study showed that climate is a major contributor to disease development based on ascospore concentrations and disease incidence. Disease incidence remained lower in 2012, with mean infection percentages of 5.8% for Winnipeg and 21.6% for Carman, which had the highest values overall in the study. At Carman, the only significant difference in infection percentages was between high and low density plots. The highest disease incidence occurred in the plots with a previous history of disease, across all canopy densities, indicating that field history is very important in controlling sclerotinia.
*Note, the much higher level of infection in Carman 2011, which was the only site with a history of previous disease incidence. Here, even the low density plots had comparable or higher disease infection than any of the densities in Winnipeg the same year.
Growers should be aware of the history of disease and inoculum levels in fields nearby. Fungicide applications may be required on susceptible crops located adjacent to fields with disease history. Application timing of fungicides can be facilitated through weather predictions focusing on precipitation and relative humidity. Additional studies conducted in larger commercialized fields are required to determine the extent ascospores arising from non-host crops can travel and infect neighbouring host crops, and the range of microclimatic and weather conditions required for successful infection in commercial fields.
Full Report PDF: n/a