This disease can occur throughout the state and is most prevalent during periods of hot, moist weather. By late summer, stem discoloration becomes more extensive. The fungus overwinters as mycelium in infected stems. Relative humidity near 100 percent and temperatures between 75 degrees F and 85 degrees F are conducive for infection. Spores of C. medicaginis are spread from plant to plant by wind and rain.
Early harvest minimizes losses.
No highly resistant alfalfa varieties are available. Rust Caused by Uromyces striatus Rust is most prevalent during summer and fall. In Alabama seedling stands have been severely injured by this disease, although normal damage is from premature leaf loss of mature plants with a resulting loss in hay quality. Rust is easily recognized by small, reddish brown, circular masses of spores that form in small spots on the upper surface of the leaflet, petioles, and stems. Leaves may shrivel and fall prematurely.