Black stem occurs wherever vetches are grown in the United States and is caused by several closely related fungi. Stem discoloration is the most distinctive symptom, although the fungi also produce large, dark, irregular lesions on the leaves. The disease can cause serious damage to hairy vetch seedlings. Root rot also occurs wherever vetches are grown. It may be caused by one or several unrelated fungi that can attack plants at all stages of growth.
Symptoms are most conspicuous in seedlings, which wilt and die.
Older plants become stunted or discolored red or yellow when infected. Roots of diseased plants are badly discolored. Gray mold, or botrytis leaf spot, sometimes causes considerable defoliation of vetch. The spots are small and dark red when young, later fading to light gray or brown with a maroon border. A disease that resembles anthracnose, but is caused by a different fungus, is prevalent on hairy vetch in the South.