The attributes of a plant disease that make forecasting economically worthwhile (8, 21) are satisfied by gray leaf spot of maize; its sporadic nature as affected by the environment, potential impact on yield, cost of control, and the value of the seed crop. Conventional approaches to developing disease forecasting models depend on an understanding of the mathematical relationships describing the biology of the system. For gray leaf spot, these elationships are not thoroughly understood. This makes a mechanistic or process-based modeling approach difficult. Satisfactory results were obtained using an empirical approach to understand the relationship of environmental and cultural factors with gray leaf spot seventy (5), laying the foundation for the development of a predictive model for this disease.