Relative to moisture, temperature seems to be a less limiting factor for the development of gray leaf spot. Once moisture requirements are met, the disease seems to develop under a wide range of temperatures. Beckman and Payne (4) reported that once periods of sustained high relative humidity were provided, gray leaf spot lesions developed readily on plants kept in the greenhouse at 22-28°C. Studying the effect of temperature on spore germination and the elongation of germ tubes of C. zeae-mayd/s exposed to 12 h of high relative humidity, Beckman and Payne (4) observed that the optimum temperature was between 22 and 30°C and no germination occurred at 36°C. The findings of Garden and Hilty (22) were similar for the effects of temperature on sporulation and redial growth of C. zeae-mayd/s on potato dextrose agar. They observed that neither sporulation nor radial growth occurred at 32°C.