Common Smut (fungus - Ustilago maydis): Common smut is easily found in fields of sweet corn. The fungus overwinters as spores in the soil or in manure. They can survive 2 or 3 years. Spores may be windborne for long distances. Younger plants are more susceptible. Any above-ground part is susceptible. Ears are most commonly infected. Hail provides open wounds and greatly increases infection. Galls are formed as the common smut fungus causes cells of the corn plant to increase in size and number. These galls at first are covered with a thin white membrane. As the gall ages, the membranes break open to reveal a black powdery spore mass underneath. The spores are blown to adjoining corn plants where infection in repeated. The smut fungus is favored by high temperatures and high moisture. Optimum spore germination occurs from 79 to 100o F. Little infection occurs below 61o F. Plants grown in soils high in nitrogen or plants damaged through cultivation are most susceptible to infection. Seed treatment is not effective and breeding for resistance has not been successful.
