1Cooperative investigations of Federal Research, Science and Education Administration, U. S. Department of Agriculture and the Department of Agronomy, Virginia Polytechnic Institute and State University. Contribution No. 356, Department of Plant Pathology and Physiology, VPI & SU. Research supported in part by the NASA Wallops Flight Center (under NASA Contract No. NAS6 2388) the Virginia Agricultural Foundation, and the Virginia Peanut Growers Association, Inc.