University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

Photo of Southern rust pustules on corn
Figure 1. Southern rust pustules of corn.
Photo of rectangular lesions of gray leaf spot.
Figure 2. Rectangular lesions of gray leaf spot.

August 10, 2007

Southern Rust and Gray Leaf Spot
Active in Nebraska Corn

Southern rust (Figure 1) was identified in corn in two additional counties this week in southern Nebraska, Gage and Clay counties. This week’s rain and very humid conditions will continue to promote disease development of southern rust, as well as gray leaf spot (Figure 2), which has also increased during the last few days.

Management

Continue to monitor fields for disease development, particularly late planted fields. These fields have the highest potential for yield loss since plants have younger leaf tissue which is more susceptible to late season foliar diseases.

After brown silks have developed, the number of available fungicides is limited because of the pre-harvest intervals (PHI) on the labels. Four systemic products are available for use. Recent label changes for both Quilt® and Tilt® indicate a new shorter PHIs of 30 days. Headline® and Quadris® both have PHIs of 7 days.

For more information on rust diseases of corn and fungicides, see the NebGuide Rust Diseases of Corn in Nebraska (G1680). Fungicide label requirements can change frequently, so always read and follow the guidelines.

Note: Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by University of Nebraska-Lincoln Extension is implied.

Tamra Jackson
UNL Extension Plant Pathologist
Amy Ziems
UNL Plant and Pest Diagnostic Clinic

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© 2007 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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