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Ecology and Epidemiology

Characterization of Puccinia polysora Epidemics in Pennsylvania and Maryland. R. N. Raid, Former graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, Present address: Everglades Research and Education Center, University of Florida, Belle Glade 33430; S. P. Pennypacker, and R. E. Stevenson. Associate professor, and research assistant, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 78:579-585. Accepted for publication 28 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-579.

Southern rust of corn epidemics, caused by Puccinia polysora, were initiated in Maryland and Pennsylvania by establishing a line source of inoculum across the width of 0.8-ha (64 128 m) field plots. The rust was most severe on lower leaves, and the severity generally decreased with successive leaf positions. Average apparent infection rates ranged from 0.110 to 0.268 and were greater (p = 0.05) at the Maryland study site than in Pennsylvania during both the 1983 and 1984 growing seasons. The velocity of spread ranged from 1.6 m/day in Pennsylvania to 9.1 m/day in Maryland. Grain yields were reduced 17.7 and 39.1%, respectively, at the Pennsylvania and Maryland field sites. These maximum reductions occurred during 1984 at a 3-m distance from the inoculum source. The yield reductions were significantly related to the area under the disease progress curves as calculated from time t0 to 35 days after anthesis. Environmental data suggest temperature may be the factor most limiting to development of southern rust of corn in northern areas of the United States.