The fungus also causes a crown and root rot. In humid areas, seed pods may discolor and shrivel. Spots on leaves are oval and dark brown with lighter center and are usually surrounded by a pale yellow to tan halo. A single lesion may cause a leaflet to turn yellow and drop off prematurely. Small brown spots on leaves enlarge to form roughly circular, reddish brown to smoky brown lesions 2-6 mm in diameter.
Heavy infections kill leaflets and cause severe defoliation.
As the season progresses, dark brown stem lesions enlarge and merge until most of the stem is discolored. Small stems, and petioles may die, resulting in further defoliation. Control Disease control in alfalfa is accomplished by using resistant cultivars and by following recommended agronomic practices which assure a vigorously growing crop. Control of rank growth by cutting or grazing will help lower the humidity in the foliage, thus reducing available moisture for pathogen growth and infection. Areas which become heavily diseased with Phytophthora root rot, Sclerotinia crown and stem rot, bacterial wilt, southern blight, or Rhizoctonia stem and foliage blight may need to be taken out of alfalfa production for two to three years or more.