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Managing corn diseases during the summer growing season

Managing corn diseases during the summer growing season

By Andi Anderson

Across much of the state, corn has experienced weather stress this growing season. Despite the wet weather and delayed planting conditions this spring, now is the time to plan for in-season disease management.

Fungal diseases affect the leaves, decreasing photosynthesis and potentially killing plants early. Ear rots like Gibberella ear rot can produce toxins that create corn marketing challenges. Each disease develops under different environmental conditions, but hybrid selection is a critical factor in assessing disease risks.

Gibberella Ear Rot

Gibberella ear rot is challenging as it creates market access issues due to DON production. Fungicides that consistently lower DON levels contain triazole, with prothioconazole being common.

Proline and Miravis Neo are effective if applied while the silks are green. Early application during full tassel is better than late with brown silks. Ground applications at 20 gallons per acre using drops or booms over the top resulted in better silk coverage.

Drones with large droplets also showed promise. Predicting the risk involves assessing weather conditions 7-21 days after R1, focusing on humidity above 80% and temperatures between 59°F and 86°F.

Foliar Diseases

Foliar diseases are easier to scout for and manage. Use the fungicide efficacy table from the Crop Protection Network to select the best fungicides based on research from land grant universities.

Tar Spot

Tar spot, typically a late-season disease in Ohio, can cause economic impact through early plant death. With late planting this year, the risk of late tar spot causing injury may increase.

Scouting for tar spot is critical and should be done weekly from tassel through R3. Lesions appear as small, black, raised spots on leaves, leaf sheaths, and husks. Tar spot favors cool weather with temperatures from 59°F to 70°F and high humidity.

Northern Corn Leaf Blight

Northern corn leaf blight prefers wet conditions and warmer weather of 64°F to 80°F. Lesions are tan and elliptical, spreading mostly by wind and rain splash. Infection requires 6 to 18 hours of leaf wetness, with lesions forming 7 to 12 days after infection.

Gray Leaf Spot

Gray leaf spot is favored by warm temperatures between 70°F and 90°F and high humidity. Lesions are gray to tan, developing between the veins and are rectangular. Lesions need 14-21 days to develop, starting on the lower leaves.


Common rust favors cool temperatures of 61°F to 77°F and 6 hours of leaf wetness. Southern rust, a late-season disease, prefers warmer temperatures of 77°F to 88°F. Common rust is usually brownish while southern rust is reddish-orange.

Common rust is on both sides of leaves, while southern rust is mostly on the top. Identifying diseases helps in choosing the best fungicides when needed.

Photo Credit: gettyimages-awakr10

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Categories: Ohio, Crops, Corn

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