Scout Info Kentucky IPM Pest Information Pages Southern Rust Symptoms Symptoms are somewhat similar to common rust, however, with southern rust the pustules(uredia) are cinnamon brown, circular to oval and densely scattered on the upper leaf surface. The chocolate brown to black stage (telia) is circular to elongate and frequently appear as circles around the uredial pustules. Southern rust pustules (containing the spores) remain covered by the epidermis for a longer time than do those of common rust. Cause Southern rust is caused by the fungus Puccinia polysora Development of the disease is favored during periods of high temperature (80 degrees F, 27 degrees C) and high relative humidity. Southern rust does not occur as often from year to year as does common rust. On susceptible hybrids, the disease can develop very rapidly during warm, humid conditions. IPM Techniques Fields should be examined every four weeks from whorl through dent stage. Scouts should observe two rows of plants 10 feet in length at several representative locations throughout the field. Report severity of the disease according to the following rating scale: 0 = no symptoms; 1 = a few pustules on a few leaves of some plants; 2 = most leaves on all plants contain scattered populated pustules; 3 = nearly all leaves of all plants contain numerous pustules, some leaves are chlorotic and dry. Plant resistant hybrids. Avoid late planting. References and Additional Information IPM-2 Kentucky IPM Manual for Corn PPA-10a Kentucky Plant Disease Management Guide for Corn and Sorghum, P. Vincelli and D.E. Hershman, Extension Plant Pathology, University of Kentucky Compendium of Corn Diseases.M.C. Shurtleff. The Amer. Phytopathol. Soc. 1980.

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