Alternaria species are simple parasites that survive saprophytically outside the host. Diseased crop debris is the primary site of survival from year to year. Resting spores (chlamydospores, microsclerotia) have been reported. The diseases are favored by warm temperatures (60-78° F) and at least 12 hours of relative humidity of 90 % or more. The fungi sporulate profusely and are spread throughout fields by wind, splashing water, equipment, and workers. The main means of introduction into new areas is on infested seed.