Crop rotation and maintaining proper potassium and phosphorus levels can aid in reducing disease. Sclerotinia Crown and Stem Rot Caused by Sclerotinia trifoliorum Sclerotinia crown and stem rot causes serious injury to alfalfa, crimson, red, and white clovers. This disease develops during periods of cool, wet weather. In Alabama this disease has been observed during February, March, and April. Sclerotinia rot generally occurs in patches, which can merge into larger areas if favorable environmental conditions last.
Initial symptoms are brown spots on leaves and petioles.
Later, leaves may turn brown, wither, and die. During cool wet weather, the white fluffy growth of the Sclerotinia trifoliorum fungus can be seen on stems of the plants. The sclerotia of S. trifoliorum lie dormant in the soil until suitable conditions for germination occur. Fruiting structures are then formed that produce numerous spores that are blown through the air and cause new infections on nearby susceptible plants. Some sclerotia remain dormant in the soil for several years.