Weather strongly influences development of gray leaf spot.
The disease develops rapidly during prolonged periods of hot, humid weather. Tillage and crop rotation are also important predisposing factors. Gray leaf spot is potentially more severe in fields where corn follows corn and reduced tillage practices are used. Prior to 1992, gray leaf spot was observed only in an occasional field in southern Indiana, and relatively few fields suffered significant yield losses. In 1993, the disease occurred widely in Indiana south of Interstate 70.