Forecasting diseases caused by Sclerotinia spp. in eastern Canada: fact or fiction?

Abstract

Diseases caused by Sclerotinia sclerotiorum and Sclerotinia minor are responsible for economically important losses on several crops in eastern Canada, including canola, cabbage, carrots, celery, lettuce, snap beans, soybeans, and white beans. For crops such as cabbage and celery, the etiology of these diseases is known, but little information is available on the epidemiology. In these crops, disease avoidance and cultural practices are the primary methods of disease management, although fungicides are sometimes applied after symptoms are observed. For other crops such as beans, canola, carrots, lettuce, and soybean, the epidemiology has been described and at least partially quantified. Based on these epidemiological studies, disease-forecasting systems have been developed for canola, lettuce, and beans, and another is currently being developed for carrots. Epidemics in snap beans are associated with ascospores infecting petals as the primary inoculum, and forecasting is based on soil moisture, rainfall, crop flowering, canopy enclosure, and apothecia. Epidemics in carrots are bicyclic and represent a different situation. Epidemics in the field are associated with infection on senescing leaves in contact with moist soil under the carrot canopy. Forecasting is based on soil moisture, canopy enclosure, senescing leaves, air and soil temperature, and the presence and number of apothecia. Epidemics in storage are associated with air temperature, rate of cooling, surface wetness, and preexisting infection. Despite the availability of forecasting systems for diseases caused by Sclerotinia spp. on several crops, there are no examples of organized monitoring or forecasting programs for these diseases in eastern Canada. Anecdotal comments suggest that the reasons for the lack of development and implementation of forecasting models include the variable severity of epidemics, a lack of registered fungicides, little or no infrastructure to deliver disease-forecasting systems, and declining prevalence of integrated pest management (IPM) programs.