Alfalfa (Medicago sativa L.) is an important crop which is grown primarily for hay production. Weather does not often allow for proper drying conditions, and hay is frequently stored at moisture contents conducive for mol growth, which reduces hay quality. A leaf screening procedure was developed for the detection of alfalfa genotypes resistant or susceptible to fungal growth after harvest. The objectives of these studies were to verify the screening procedure; to determine characteristics associated with fungal growth; and to select a susceptible and a resistant population for future studies. Verification studies conducted to validate the screening procedure included comparisons of fungal growth when whole plants were cut, chopped and stored under warm humid conditions in the laboratory, and simulated field trials that evaluated mold accumulation during wilting and bale storage. Four genotypes that were previously identified as having low, variable and high susceptibility to fungal growth after harvest were used for the verification studies. The extent of fungal growth on plant material that was chopped and incubated under conditions conducive to molding was measured by glucosamine analysis. (Abstract shortened by UMI.)