While brown stem rot, Phytophthora root rot, sudden death syndrome and the soybean cyst nematode generally are regarded as the most significant diseases of soybean in the North Central States, Sclerotinia stem rot, also called white mold, has been a problem in Minnesota, Wisconsin and Michigan for many years. Beginning in 1992, and again in 1994, Sclerotinia stem rot developed throughout the northern range of the North Central Region. Nationally, the disease is considered to be minor because it has not involved a high percentage of the national soybean acreage. Possibly this situation has changed and Sclerotinia stem rot will be an annual threat to soybean production in more of the Region. Chamberlain (1951) was the first to make a detailed report on Sclerotinia stem rot in the mid-west after he observed localized, but severe outbreaks of the disease in lllinois in 1946. Chamberlain (1951) summarized his findings by the following quote; 'There appears to be no ready explanation as to why Sclerotinia stem rot, certainly one of the least prevalent of soybean diseases, can cause such severe but localized damage". After almost 50 years, more is known about factors that impact on the incidence and severity of this disease, but an element of mystery still remains as to why sudden outbreaks occur.