The Southern Corn Leaf Blight Epidemic

A dramatic shift in the genetics of host-parasite interaction and balance occurred in the U.S. corn crop in the 1970 growing season. Southern corn leaf blight incited by Helminthosporium maydis Nisikado & Miyake evolved from a minor disease that causes an average annual loss of less than 1 percent, to one that caused more than the 12 percent average expected from all diseases of corn in the United States. In 1970 the losses to corn leaf blight approaches 710 million bushels. Reserves of corn and other grains ease the impact on the economy and food supplies but there are important domestic and foreign effects of the loss. The epidemic illustrates the vulnerability of our food crops to pests. Sources of genetic resistance to the new race of Helminthosporium maydis are available. The seed industry estimates that for 1971 enough resistant and partially resistant seed to plant about one-half of the crop may be available. Adequate supplies are expected in 1972. Sustained research programs are essential in protecting our food supplies from potential losses of catastrophe magnitude. Several professional groups, including the American Phytopathological Society and the Entomological Society of America, have urged that a program and facilities be established for the study of exotic pests that threaten our agriculture so that controls may be found before the pests are here. Such a program would be desirable but covers only one aspect of the problem. What is really needed is an overall strengthening of research on crop pests.