Sclerotinia crown and stem rot (SCSR), caused by Sclerotinia trifoliorum Eriks., causes serious spring losses in some fall=sown, no-tillage alfalfa fields. In microplots artificially infested with sclerotia, greatest numbers of apothecia were found during November and December. Temperature and rainfall had significant impact on apothecium development. A proposed prediction method for apothecium appearance considers monitoring mean soil temperature. For apothecium initiation to occur, it was necessary for sclerotia to be subjected to an estimated 17 days of temperature at or below 15 C before apothecium production occurred. Soil temperatures were usually below 10 C at the time of apothecium appearance. Greatest numbers of apothecia occurred between 5-10 C. Rainfall influenced the number of apothecia, with significant increases occurring early in the 1984-85 production period. / Master of Science