Gray Leaf Spot

Disease Facts

Gray leaf spot is caused by the fungus Cercospora zeae-maydis.

Epidemics of gray leaf spot have been observed in New York State in the Southern Tier and the Hudson River Valley. New hot spots of the disease have been reported in the Mohawk Valley and the Leatherstocking Region.

Gray leaf spot is favored by wet humid weather as often found in valley microclimates. Additionally, it is favored in situations with reduced tillage and continuous corn.

Airborne spores are spread locally and regionally from corn debris.

Management Strategies

Management strategies for gray leaf spot include tillage, crop rotation and planting resistant hybrids. See the Handy Bt Trait Table updated for 2023 for U.S. Corn Production from the University of Michigan for recommendations.

Fungicides may be needed to prevent significant loss when plants are infected early and environmental conditions favor disease.

Symptoms

Symptoms of gray leaf spot are usually first noticed in the lower leaves.

Initially, lesions of gray leaf spot begin as a small dot with a yellow halo.

Lesions will elongate over time running parallel to the veins becoming pale brown to gray and rectangular in shape with blunt ends. These lesions can be described as having the appearance of a “matchstick.”

Lesions may eventually coalesce killing the leaves.

Leaves appear grayish in color due to the presence of fungal spores.