Gray leaf spot of corn, while of little consequence in the US before 1970, has become a major concern to many corn producers in recent years. Serious outbreaks of the disease first occurred in the early to mid 1970s in low-lying areas in the mountainous regions of Kentucky, North Carolina, Tennessee and Virginia. Since this time, the disease has spread to most corn-producing areas of western Kentucky and parts of Delaware, Illinois, Indiana, Iowa, Maryland, Missouri, Ohio, Pennsylvania and west Tennessee.
Vincelli, Paul and Hershman, Donald E., "Gray Leaf Spot of Corn" (1994). Agriculture and Natural Resources Publications. Paper 7.