VIEW ARTICLE

Ecology and Epidemiology

Epidemiology of Sclerotinia Stem Rot of Soybean in Ontario. G. J. Boland, Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1; R. Hall, Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1. Phytopathology 78:1241-1245. Accepted for publication 6 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1241.

The epidemiology of Sclerotinia stem rot of soybean in Ontario was investigated in 1981 and 1982. Apothecia of Sclerotinia sclerotiorum appeared after the development of a crop canopy during mid to late July and were present for 5–6 wk thereafter. Soil matric potentials were generally ≥ –5 bars during the 2 wk preceding the occurrence of apothecia. Epidemics started in early to mid August and continued until near crop maturity. Disease first appeared after closure of the crop canopy, after crop flowering had started, after apothecia appeared within the crop, and after rain had initiated periods of plant surface wetness lasting for 40–112 hr. Mean daily air temperatures were in the range of 12–24 C. Disease development required 70–120 hr of continuous plant surface wetness at 20 C in controlled-environment inoculations with ascospore suspensions.