Check Hybrids for Resistance to Corn Rust!

Denise McWilliams, NDSU/UM Extension Crop Production Specialist
(Taken from Minnesota Crop Newsletter)

Corn rust is starting to show up in the Midwest. This corn disease shows up as rusty circular to elongate disease areas that are brown to cinnamon brown from the pustules scattered over the leaf surface that then become brownish black as the disease matures. Severe infection from common rust can cause chlorosis and death in the leaves and leaf sheaths of corn. Disease infection occurs in mid-June to mid-July under moderate temperatures (61F to 77F) and high relative humidity (greater than 95%). About six hours of moisture is required for the disease to germinate and infect. Common rust is most effectively controlled by growing resistant hybrids. General resistance results in reduced severity of disease infection.

Fungicidal control is possible but usually not economic unless the application is made while there is limited secondary inoculum from the disease and if the area effected includes most of the field. So far, no cases have been confirmed in the North Dakota or Minnesota Red River Valley with reports limited to Illinois, Indiana, Iowa and Missouri where recent rainfall was heavy. Check hybrids now to confirm the hybrid you are growing is not showing any disease problems. Also, check fields to confirm recent growth with the sunshine on Sunday. Over the weekend, continuing growing degree days and sunshine has helped corn to leap-frog in height. Quick growth may confirm brittle stalks so if any field operations such as additional fertilizer application are made, realize the corn can be easily broken if care is not taken when moving through corn fields.

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

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Last Revised July 20, 2000.
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