smut, plant disease primarily affecting grasses, including corn (maize), wheat, sugarcane, and sorghum, caused by several species of fungi. Smut is characterized by fungal spores that accumulate in sootlike masses called sori, which are formed within blisters in seeds, leaves, stems, flower parts, and bulbs. The sori usually break up into a black powder that is readily dispersed by the wind.
Many smut fungi enter embryos or seedling plants, develop systemically, and appear externally only when the plants are near maturity. Other smuts are localized, infecting actively growing tissues. Control includes growing resistant varieties in noninfested soil, treating seeds with a fungicide, using disease-free transplants, and destroying infected plants or plant parts before the spores are released. See also bunt; corn smut.