Scattered plants turn yellow, then wilt and die. A white, cottony growth of mycelium is visible on the lower stems and crowns during cool, wet weather. Infected stems become soft and mushy at the base. Crown infection leads to plant death. Small, hard, black sclerotia are produced on or inside stem and crown tissue.
Snow cover increases the development of Sclerotinia crown and stem rot during the winter.
Sclerotinia is less damaging to alfalfa than to clovers. Use sclerotia-free seed to avoid introducing the disease. Rotate with cereal or grass crops. Where sclerotinia was severe, wait three to four years before replanting forage legumes. Alfalfa Stem Nematode Alfalfa stem nematode.