Gray leaf spot of maize (Zea mays), caused by Cercospora zeae-maydis (68), has more than lived up to the 1983 prediction of Latterell and Rossi as a disease on the move (34). Sometimes referred to as a “government-made disease” because reduced tillage resulting from federal incentives contributed to its proliferation, gray leaf spot has continued to expand its geographic distribution and increase in intensity over the past 25 years. Gray leaf spot is now recognized as one of the most significant yield-limiting diseases of maize (corn) worldwide (38,43,79). It now poses a serious threat to maize production in many areas of the eastern United States and, more recently, in large areas of the U.S. Corn Belt and Africa (38,42– 44,52,73,80). In August 1995, the Wall Street Journal reported yield losses due to gray leaf spot as high as 50% in some U.S. maize fields (72). Garst Seeds estimates that gray leaf spot has damaged as much as 9.3 million ha of maize in Iowa, Illinois, Indiana, Ohio, Kentucky, and Tennessee, and that an additional 11.3 million ha in other areas of the United States could potentially be affected (25). They estimate that gray leaf spot is increasing in extent at a rate of 80 to 160 km each year, and the disease is now endemic throughout much of the midwestern Corn Belt.