Gray Leaf Spot

Cercospora zeae-maydis

Corn leaf with numerous gray leaf spot lesions
Corn leaf with numerous gray leaf spot lesions. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Gray leaf spot is a potentially serious fungal disease of corn. It is most serious during prolonged warm, humid, and wet conditions.
Gray leaf spot lesions are brown or grey, often with yellow halos. Major leaf veins block the expansion of the disease. Hybrids with resistance to gray leaf spot will have smaller lesions that do not expand to the veins.
Leaf with gray leaf spot lesions
Leaf with gray leaf spot lesions. Note how the disease is confined between leaf veins. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Gray leaf spot attacks the leaf tissues, reducing leaf area and hence yield. Damage typically begins in the lower leaves and moves up the plant, with the most severe damage occurring when the disease is at or above the ear leaf. The extent of lesion growth and hence damage is influenced by the resistance of the host plant.
Fungicides applied at VT-R1 provide some level of control of gray leaf spot. Treatment is most likely to be cost effective if the disease is at or above the ear leaf. Always read and follow all label instructions.
Crop rotation and tillage can help to reduce the level of disease in a field since the disease overwinters in crop residue.