An Epidemic of Sorghum Downy Mildew in Nebraska in 1987. Stanley G. Jensen, United States Department of Agriculture, Agricultural Research Service, Lincoln, Nebraska 68583. Ben Doupnik, Jr., David Wysong, and Blaine Johnson. Department of Plant Pathology, University of Nebraska; and United States Department of Agriculture, Agricultural Research Service, Lincoln, Nebraska 68583. Plant Dis. 73:75-78. Accepted for publication 31 August 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/PD-73-0075.

Sorghum downy mildew was found in 17 of 34 counties surveyed in south central and southeastern Nebraska in 1987. Grain sorghum, sudangrass, and shattercane were infected, but no maize was found with symptoms. The most common symptoms observed were leaf spots caused by conidial infections and systemic stripes on tissues that developed after the main stalk. In some grain sorghum fields in south central Nebraska, however, up to one-third of the plants had early systemic infection of the primary stalk, resulting in significant yield reduction. We hypothesize that the exceptionally early and warm spring, with soil temperatures 5–8 C above normal, contributed to the epidemic, and we offer a theory to account for the presence of inoculum where the disease had not been seen before.

Keyword(s): epidemiology, Peronosclerospora sorghi, Sorghum bicolor.