First Report of Downy Mildew on Sunflowers Caused by Plasmopora halstedii in Kansas. D. J. Jardine, Department of Plant Pathology, Kansas State University, Manhattan 66505-5502. and T. J. Gulya, USDA Northern Crop Science Laboratory, Fargo, ND 58105. Plant Dis. 78:208. Accepted for publication 25 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0208B.
Climatic conditions during July 1992 were excessively cool and wet. Sunflowers (Helianthus annuus L.) exhibiting symptoms of downy mildew, caused by Plasmopora halstedii (Farl.) Berl. & deToni, at the V4 (four true leaves) stage of development were observed in several fields in Sherman County in northwestern Kansas. These plants were stunted, and sporangiophores and zoosporangia of P. halstedii were present on the underside of the leaves. Race identification of three isolates was determined using the whole-seedling immersion technique (1) with differential cultivars IS-003, RHA-265, RHA-274, DM-2, IS-2000, and 803-1. Two isolates were determined to be race 4, and the third was identified as race 3. This is the first report of P. halstedii on sunflowers in KansasReference: (1)T. J. Gulya et al. Helia 14:11, 1991.