Generally, any of numerous plant diseases caused by fungi. The ruining of crops by mildew was one of the calamities experienced by unfaithful Israel. (Deut. 28:22; 1 Ki. 8:37-39; 2 Chron. 6:28-30; Amos 4:9; Hag. 2:17) It has been suggested that the mildew of the Bible may be grain rust (Puccinia graminis). This serious parasitic disease deprives plants of needed nourishment and water and thus can cause the kernels of grain to dry up. Small rust-colored spots appear on the stems and leaves of attacked cereal plants.