The fungus survives and overwinters in dead stem and crown tissues. Spores are splashed by rain to new stems. Also attacks alfalfa. Leaves and stems eventually become blighted, turning dark brown. The disease occurs only during warm, humid weather in second or later cuttings that go beyond full bloom.
Diseased forage produces the chemical slaframine, which is toxic to livestock.
Avoid letting second cutting go to seed. Circular tan, brown or black spots on leaves. Leaves fall off when infections are severe. These fungi survive in undecomposed leaf tissue on the soil surface. Spores are spread by air currents or rainsplash.