Corn Smut

Ustilago maydis

This fungal disease mostly infects the ears of middle and late season corn plants. The disfiguring swollen grayish-white growths start growing inside the husk, but expand out of it as they develop. The mature fungus releases a cloud of dark spores that can infect nearby plants or remain in the soil.

Smut overwinters on crop debris and can form resting spores that remain viable for years. Remove infected ears before they turn black and release spores. You can reduce infection by crop rotation and by using resistant cultivars.

Image: William M. Brown Jr., Bugwood.org