A Proposed International System for Designating Races of Plasmopara halstedii. W. E. Sackston, Emeritus Professor of Plant Pathology, Department of Plant Science, Macdonald College of McGill University, Ste. Anne de Bellevue, Que., Canada H9X 1C0, and T. J. Gulya, Research Pathologist, and J. F. Miller, Research Geneticist, USDA-ARS, Oilseeds Research Unit, Northern Crop Science Laboratory, Fargo, ND 58105. Plant Dis. 74:721. Copyright 1990 American Phytopathological Society. DOI: 10.1094/PD-74-721.