ECOLOGY AND EPIDEMIOLOGY OF SCLEROTINIA WILT OF WHITE BEANS IN ONTARIO

Abstract

The distribution of sclerotinia wilt (Sclerotinia sclerotiorum) in commercial white bean (Phaseolus vulgaris L.) crops was determined by a three-stage sampling of plants three times in each of two growing seasons. Crop growth characteristics, soil conditions, and agricultural practices in crops with and without the disease were compared. The disease has not previously been reported on dry bean seedlings in Ontario. It was found in 1969, 5 days after an unusually warm rainy period. The disease usually appeared after flowering and when the first pods were at least 8 cm long. Infected crops were distributed throughout the bean-growing area, except in the lee of Lake Huron, where the disease occurred only in crops planted in north–south rows. In general east–west (and southwest–northeast) planted crops had less disease. Other conditions significantly associated with the presence of disease were early date of planting, low plant populations, high dry weight per plant, high crop canopy density, and soil pH. Soil fertility, soil texture, and recent cropping history of the field were not associated with disease occurrence. Sclerotinia wilt reduced yield 1.3% in Ontario in 1969–70.