disease of plants caused by the fungus Ustilago maydis, which attacks corn (maize) plants, affecting any aboveground part. The early signs of an attack are whitish galls that later rupture to release dark spores capable of infecting other corn plants. Affected plants are often distorted. The disease is most vigorous in warm weather. Spores overwinter in soil and in corn litter and then infect the next year's planting.