Caused by the fungus Ustilago maydis, this disease can affect all above ground parts of the plant but is most economically significant when it attacks the ears. It causes the corn kernels to swell up into tumor-like 4-5″ wide galls that are first white but become blue-gray and full of black powdery spores with maturity. Although the galls are edible and valued in Mexican cuisine as huitlacoche, they are considered undesirable to many corn cob devotees. Dry conditions, mechanical injury to plants, and excess nitrogen favor smut infestations. Photo Credit Kai Hirdes Wikipedia
Control:
- Remove any infected ears immediately and dispose of them so that the spores of the fungus can not spread.
- Wash tools, hands, and clothing that may carry spores.
- Use resistant cultivars
- Rotate crops yearly because smut spores may over winter in the soil and corn plant debris
- Spray with a solution of 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil, and 1 teaspoon of liquid soap (not detergent) per gal of water. Repeat every 2 weeks, more often if rain washes the solution away.
- Avoid damage to the plants that may allow spores to enter
- Do not over feed the plants with nitrogen as excess nitrogen encourages infestation