Summer Black Stem and Leaf Spot of Alfalfa
Summer black stem and leaf spot is caused by the fungus Cercospora medicaginis. Summer black stem and leaf spot reduces yield and forage quality and generally impacts the second and third alfalfa cuttings. Symptoms first appear on lower leaves, but progress up the plant over time. Irregular, brown lesions with yellow halos form on leaves and can be observed on both leaf surfaces. Presence of fungal spores cause lesions to turn silvery. Defoliation can occur when leaves have as few as two lesions. Stems initially show small, dark lesions that may grow to cover large portions of the stem.
Summer black stem and leaf spot appears as irregular brown lesions with yellow halos; lesions can be observed on both leaf surfaces.
Deborah Samac
Summer black stem and leaf spot lesions.
Craig Grau
C. medicaginis survives within infected stems. High humidity and warm temperature within a dense plant canopy favor summer black stem and leaf spot development.
Avoid planting particularly susceptible alfalfa cultivars. Losses can be reduced by harvesting early, when flower buds first appear.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Summer black stem and leaf spot appears as irregular brown lesions with yellow halos; lesions can be observed on both leaf surfaces.
Summer black stem and leaf spot lesions.
Gallery images courtesy Deborah Samac and Craig Grau.
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