In wet soils, root rot may be a problem affecting soybean. Pathogens such as Pythium species, Rhizoctonia solani, and Fusarium oxysporum can cause root rot in soybean and cause considerable yield loss. Registered seed treatments are recommended as are use of resistant varieties to reduce the risk.
Sclerotinia sclerotiorum or white mould may infect soybean especially in wet years. Initially, flower petals are infected and the disease continues to grow affecting the stem and pods, eventually causing the top of the plant to die. Rotations with non-host crops might help reduce the incidence of this disease. However, many crops and weeds are hosts to this disease. Closely spaced plants that form a canopy quickly, early in the season are at increased risk.
Powdery mildew is also a potential problem in cool years, however, it will generally only cause yield reduction if it occurs in July.
Information adapted from the Saskatchewan Ministry of Agriculture.