Predicting diseases caused bySclerotinia sclerotiorumon canola and bean — a western Canadian perspective

The majority of the life cycle of Sclerotinia sclerotiorum is spent in the soil as sclerotia. Depending on various environmental factors, the sclerotia germinate to form either apothecia or mycelium. Ascospores formed within the apothecium are spread by air currents and initiate infection when they contact a susceptible host. After invasion of host tissue, sclerotia are formed and eventually return to the soil environment, survive adverse environmental conditions, and await the next susceptible crop. In economically important crops such as canola (Brassica spp.) and bean (Phaseolus vulgaris), S. sclerotiorum causes considerable damage, and fungicide application is a recommended disease management strategy. In recent years, a general awareness concerning disturbance and pollution of the environment as well as the difficult economic conditions facing many producers has led to an increasing interest in optimizing the use of pesticides. Using pesticides only when needed requires effective disease-forecasting systems. In this paper, we review that portion of the life cycle dealing with the development of apothecia, production of ascospores, and host infection with respect to the prediction and management of diseases caused by S. sclerotiorum. The current disease-forecasting systems for S. sclerotiorum that are available to growers in western Canada, as well as those that are in the process of development, will also be discussed.