Gray leaf spot is caused by the fungal pathogen, Cercosporazeae-maydis.
This disease is favored by warm temperatures over 80°F, and extended periods of high humidity.
Fungal spores overwinter in corn crop residue, increasing chances for infection on non-rotated crops.

Identification

Gray leaf spot symptoms begin as small brown lesions in the lower canopy, and travel upwards as the season progresses.
As lesions expand, they are limited by leaf veins, giving them a distinct, rectangular shape (Figs 1 and 2).
Lesions become grayer in color as sporulation begins (Fig 3).
Leaves can easily be overtaken by the rapid development of this disease.

Fig 1: Corn leaf displaying GLS symptoms

Fig 2: An early GLS lesion, shapes are easier to identify when backlit

Fig 3: A sporulating GLS lesion

Management

Cultural practices like tillage and crop rotation can decrease inoculum load.
Resistant hybrids are available that can tolerate GLS.
Fungicides labeled for use on GLS can be sprayed on corn according to the label.

References

Crop Protection Network . (2022, January 27). Retrieved from Gray Leaf Spot of Corn: https://cropprotectionnetwork.org/encyclopedia/gray-leaf-spot-of-corn

UD Cooperative Extension. (n.d.). Gray Leaf Spot on Corn.Retrieved from Agriculture & Natural Resources: https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/gray-leaf-spot-on-corn/

Authors: Madeline Henrickson and Dr. Alyssa Koehler

UD Cooperative Extension

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