Anthracnose Crown and Stem Rot of Alfalfa
Anthracnose crown and stem rot is primarily caused by Colletotrichum trifolii. This disease can be particularly devastating when it occurs in the crown, as it causes plant death. Lesions typically occur on lower stems and are large oval- or diamond-shaped with a sunken appearance. Lesions are tan with dark borders and may have tiny black acervuli (fungal fruiting bodies) within them. As lesions grow together, stems can die, causing a “shepherd’s crook” appearance of wilted stems. The anthracnose pathogen can spread from stem lesions to the crown in susceptible plants. When this occurs, stems will often die and appear “bleached.” Woody crown tissue will show an internal bluish-black discoloration that spreads throughout the crown in susceptible plants, resulting in plant death. “Summer decline” results from anthracnose infection of susceptible cultivars.
Anthracnose crown and stem rot stem lesions.
Craig Grau
Shepherd's crook symptoms indicative of anthracnose crown and stem rot.
Deborah Samac
Warm, wet weather favors pathogen infection and subsequent disease development. C. trifolii can survive on crop residue and within infected crowns.
Anthracnose crown and stem rot disease cycle in alfalfa.
Mimi Broeske, Nutrient and Pest Management Program, University of Madison-Wisconsin
Resistant alfalfa cultivars are available and should be used where anthracnose is a problem. Practice harvest-equipment sanitation to mitigate field to field pathogen spread. Mow younger, non-infected stands first.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Shepherd's crook symptoms indicative of anthracnose crown and stem rot.
Anthracnose crown and stem rot stem lesions.
Anthracnose crown and stem rot stem lesions on alfalfa. Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org.
Anthracnose crown and stem rot crown rot phase.
Anthracnose crown and stem rot wilting.
Alfalfa field with anthracnose crown and stem rot.
Gallery images courtesy Deborah Samac, Craig Grau, and Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org.
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