Southern Rust Update in Nebraska
August 1, 2014
This week southern corn rust (Figure 1) was confirmed in Nemaha, Pawnee, and Richardson counties in southeast Nebraska and in Clay County in south central Nebraska. Last week it was confirmed in Otoe County. (See report in CropWatch.)
Historically, southern rust spread to new fields and areas of the state has taken from several days to weeks — with many areas not developing rust. Applications of systemic fungicides can provide protection for 21 to 28 days, so application timing becomes very important for optimizing the benefits of these products. Because we have many weeks of grain fill left in some fields, we recommend closely monitoring for this disease in fields and delaying fungicide application decisions until the threat of rust is imminent to take maximum advantage of the residual activity of these products.
We will continue to monitor the development of southern rust in Nebraska and report it by county on the IPM PIPE Southern Corn Rust monitoring website.
NOTE — Not all states participate in updating the maps on this website. Thus, the maps on the website may be incomplete or not be up-to-date, and so they should not be strictly relied upon for disease confirmation and incidence. Refer to the reports from local university plant pathologists, diagnostic laboratories and county Extension offices for the most recent information regarding southern rust distribution.
The characteristics used for differentiating between common rust and southern rust are described and illustrated in the NebGuide, Rust Diseases of Corn in Nebraska. The simplest and most reliable way to differentiate the diseases without a microscope is to examine both leaf surfaces for spore production. Southern rust spore production is usually limited to the upper leaf surface and tends to be tan/orange in color. However, in some cases this year, we have observed common rust symptoms that looked surprisingly similar to southern rust, making it difficult to differentiate them based on appearance.
The most reliable method for identifying corn rust diseases is based on examination of microscopic spore characteristics, which can be done quickly in the laboratory. If you need assistance with a diagnosis, submit samples to the UNL Plant and Pest Diagnostic Clinic.
UNL Extension Plant Pathologist
Director, UNL Plant and Pest Diagnostic Clinic