Southern rust confirmed in South Dakota

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Farm Forum

BROOKINGS — Southern rust was recently found in Brookings County at very low incidence and severity, said Emmanuel Byamukama, SDSU Extension Plant Pathologist.

According to USDA’s Crop Progress and Condition report of September 2, 2014, 41 percent of the corn had dented.

“Therefore, the southern rust developing on corn may not significantly reduce yield except for corn planted late,” Byamukama said.

He explained that Southern rust is caused by Puccinia polysola and does not overwinter in South Dakota. Spores are blown from southern states northwards. “This rust thrives under humid and warm weather conditions. The optimum temperature for this disease to develop is 82 degrees Fahrenheit and at least six hours of leaf wetness. With cooler temperatures in the forecast, southern rust progress in corn may be curtailed,” he said.

He explained that Southern rust can be differentiated from common rust by the color of the pustules and the arrangement of the pustules on the leaf. “Common rust has elongate golden brown to cinnamon brown pustules that are randomly distributed on the upper surface of the leaf. The common rust pustules can also develop on the underside of the leaf. Southern rust pustules are orange in color and are clustered on the upper surface of the leaf,” Byamukama said.

All corn hybrids are susceptible to southern rust as opposed to common rust, where resistance and tolerance have been incorporated to most hybrids. Producers whose corn has not yet dented should scout their field and assess the extent of southern rust development. Southern rust severity reaching 15 percent on ear leaf and above may require a fungicide application.

To learn more, visit iGrow.org.