Head smut

Tassels and ears of infected plants are often replaced by smut sori. On tassels, individual spikelets may be infected. Ears are usually entirely aborted. Infection occurs in seedlings and the fungus grows systemically into the reproductive parts of the plant. Temperatures of 70 to 82 degrees Fahrenheit and low soil moisture favor infection. The disease is effectively controlled by resistant hybrids. Planting early when soils are too cool for teliospore germination and use of systemic fungicide seed treatments are partially effective.

Taken from Corn Production Handbook, KSU Extension