Diseases of alfalfa (
Stemphylium leaf spot
Stemphylium leaf spot is caused by the fungus Stemphylium botryosum biotype C-T. This biotype has been described as the cool weather strain common in alfalfa in cool wet springs. The fungus produces light tan lesions that are defined by a dark border (photo 1). The lesions vary in size, progressing only when there is plenty of moisture and before the border is formed. Infections reduce the quality of the hay, but are rarely severe enough to cause defoliation.
Infected alfalfa should be cut as soon as possible to reduce moisture and spore production. No other control measures are practiced.
1 
July 14 , 2006