Distribution of Puccinia polysora in Indiana and Absence of a Cool Weather Form as Determined by Comparison with P. sorghi. R. A. Schall, Plant Pathologist, APHIS, USDA, Lafayette, IN 47901. J. W. McCain, Graduate Research Assistant, and J. F. Hennen, Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Plant Dis. 67:767-770. Accepted for publication 6 December 1982. 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, 1983. DOI: 10.1094/PD-67-767.

Southern maize (Zea mays) rust, caused by Puccinia polysora, has now been found widely in Indiana. Weather conditions at the time of disease appearance each year were reviewed. Although southern maize rust was severe in some years, correlations between favorable weather and disease appearance did not indicate that the pathogen had developed new forms that could infect corn during cool weather or overwinter in Indiana. Southern maize rust appeared later in 1978–1981 than common maize rust, caused by P. sorghi, and followed periods of southerly winds associated with rainfall and temperatures warmer than those that favored common maize rust. Morphology and taxonomy indicate that P. sorghi should be considered the valid name for the common rust pathogen and P. maydis is a synonym.