Gray leaf spot is one of two common foliar fungal diseases of corn. It is caused by either Cercospora zeae-maydis or Cercospora zeina and appears as grey rectangular, brown to gray necrotic lesions that run parallel to the leaf, filling the spaces between the secondary leaf veins. Plants are especially susceptible to infestation in wet humid weather. It is considered the number one disease for corn growers and is hard to eradicate because it overwinters in the debris on the soil surface. Photo Credit Daren Mueller, Iowa State University, Wikipedia
- Remove infected plants 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
- Crop rotation
- Water in the morning using drip irrigation to reduce the time that moisture is on the leaves
- Mulch plants to reduce the effects of rain splashing spores onto plants
- Increase air circulation by increasing space between plants or trimming excess foliage
- 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.
- Spray with a prepared solution of Bacillus subtilis about every 2 weeks or when rain has washed it off the leaves.
- For very severe infestations spray with copper or sulfur, heeding cautionary warnings on the containers. The copper application will require special equipment.