DISEASES OF CORN - GRAY LEAF SPOT

Gray leaf spot is caused by the fungus Cercospora zeae-maydis. In contrast to most leaf spots that have circular or ellipsoidal lesions, lesions of gray leaf spot tend to be long and rectangular, and are typically restricted by veins of the leaf. Lesions are pale brown, gray or tan, and are opaque. When the disease is severe, individual lesions may merge, the entire leaf may die and total defoliation of the plant is possible. Weakening of plants due to gray leaf spot (and leaf spot diseases in general) may result in lodging.

The fungus that causes gray leaf spot overwinters in corn debris and thus the disease tends to be most prevalent where continuous corn is produced and no-till practices are used. The causal fungus tends to be favored by high temperatures, and thus gray leaf spot is more common in the southern US. However, reports of the disease have recently increased in the upper mid-west, perhaps due to the increased use of no-till practices. Clean plowing and crop rotation help control this disease. Resistant hybrids are available and should be used when the potential for the disease is high. Chemical control is also possible, although likely to be economical only for seed corn production.