Sclerotinia Crown and Stem Rot of Alfalfa
Sclerotinia crown and stem rot is caused by the fungus Sclerotinia trifoliorum. Symptoms include light brown, rotted crown tissue that darkens and turns soft as disease develops. Plants may rot away entirely prior to spring. Signs include white mycelium (fungal growth) colonizing dead stem tissue, causing it to appear white; sclerotia (fungal survival structures) in or next to rotted plant tissues; and fuzzy, white, web-like growth covering stems and crowns. The web-like growth can spread the pathogen to new plants, and newly infected stems become discolored and rotted. Cool, wet weather favors mycelium development and infection of new plants. Late summer- and early fall-seeded stands are at highest risk for disease development. Single plants or small patches may be killed when the disease develops within established stands.
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem.
Craig Grau
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem.
Craig Grau
S. trifoliorum survives as sclerotia in soil. Mushroom-like apothecia germinate in the fall when the soil is cool and wet. Spores are produced in the apothecia which spread to alfalfa plant tissue where they infect and the fungus then colonizes the plants. Prolonged snow cover can increase disease severity.
Plant disease-resistant alfalfa cultivars in areas where disease risk is high. Because newly established plants are more susceptible to Sclerotinia crown and stem rot, plant in the spring, or as early as possible during late summer and fall. Tillage can bury sclerotia and prevent apothecia germination. Management that reduces S. trifoliorum inoculum, such as planting sclerotia-free seed, should also be practiced.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem. Craig Grau.
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem. Craig Grau.
Sclerotinia crown and stem rot on alfalfa stem. Craig Grau.
Apothecia of Sclerotinia trifoliorum growing from sclerotia. Craig Grau.
Sclerotinia crown and stem rot symptoms on alfalfa. Maira Duffeck.
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem. Maira Duffeck.
Sclerotinia crown and stem rot symptoms and signs on alfalfa stem. Maira Duffeck.
Gallery images courtesy Craig Grau and Maira Duffeck.
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