Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorumis endemic to North Dakota canola production areas. Development of ascosporic epidemics caused by S. sclerotiorum occurs in three stages: apothecia formation, flower/leaf colonization, and stem colonization.The objective of this study was to model the second stage as function of leaf wetness duration and incubation temperature. The study was conducted twice in growth chambers using a randomized complete block design with three replications. Fresh canola flowers were dry-inoculated with S. sclerotiorumascospores and placed on leaves of individual plants. Each plant constituted a replication and received ten inoculated flowers.Inoculated plants were incubated at 10, 25, or 30º C with 6, 10, or 18 h of wetness daily for six days. The number of foliar lesions formedon each plant was recorded daily and expressed as percentage. Results of fitting five temporal models of disease progress to this data will be presented. Modeling the temporal progress of disease development as a function of leaf wetness duration and temperature will improve our understanding of how SSR epidemics progress in field conditions.