The development of Sclerotinia blight, caused by Sclerotinia minor Jagger under various environmental conditions, was studied in field plots of peanuts (Arachis hypogaea L.). The peanut plant canopy was modified to produce desired environmental parameters. The modifications included the thinning of canopy foliage to allow air circulation that would decrease canopy humidity and the addition of water-filled troughs under an unthinned canopy that would increase humidity. Canopy relative humidity and soil moisture under the canopy was decreased by canopy thinning. Following infection by S. minor, the number of infection foci and disease development was reduced in the thinned canopy; however, thinning also reduced pod yield. Disease development was not increased, nor was yield affected by the addition of the water-filled troughs which increased humidity levels in the canopy. Soil moisture and canopy light interception were important variables in multiple linear regression models for the disease severity index and longest lesion length in the thinned and unthinned-trough plots.