Corn Smut

Question: What are these dark colored galls on the ears or tassels of my corn?

Answer: Most likely your corn is infected with the pathogen Ustilago maydis, more widely known as common smut. Common smut is a fungus that typically is found on the ears and tassels of the corn plant in conspicuous dark galls that replace kernels and my reach several inches in diameter (although most samples brought to the Extension office are about one inch or so in diameter). You will see them in clusters on your ear of corn. While they ruin your ears of corn they are not harmful to humans. Corn smut is considered a delicacy in Mexico. One has to eat it before the spores become ripe, when the insides are still moist and the gall is white to gray on the outside. As the galls mature, the interior darkens and turns into masses of powdery black spores.

The spores overwinter in the soils. Under the right conditions these form secondary spores that are carried by the wind or by water to young growing plants. Common smut favors dry conditions and temperatures between 78 and 93 degrees Fahrenheit. Plants that are infected should be removed and destroyed by burning or burying. The stocks may be fed to livestock but the spores are typically not destroyed. Remove infected plants before the galls mature and break open releasing the spores.

Some sweet corns are resistant to common smut so if this pathogen is a problem in your garden you may want to look for these varieties. Remove all plant debris from the infected area. Also, rotate your vegetable crops. Do not plant corn in the same location for at least three years. While common smut is destruction and unsightly, it commonly will not infect more than 20% of your crop.

Images of common smut of corn

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More extensive report on common smut