This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension. Southern rust in corn has been confirmed in 10 counties including Butler County in east central Nebraska as well as frogeye leaf spot (Figure 1) in soybeans in Dodge, Saunders, and Washington Counties. Warm temperatures & high humidity promote the development and spread of these two diseases.
Southern rust does not overwinter on residue and must be blown in by the wind from the south. Most hybrids do not have good resistance to southern rust and it is important to scout fields, especially later planted fields since an infection during early growth stages could lead to greater yield losses if not controlled. Southern rust tends to occur on the upper leaf surface and be tan to orange in color whereas common rust is darker orange to red. For more help in identifying southern rust, visit CropWatch and send a sample into the UNL Plant and Pest Diagnostic Clinic for confirmation. Timely fungicide application can be very effective in controlling southern rust in corn.
In soybeans, frogeye leaf spot infection occurs more readily on newer leaves and this is why is can be observed in the upper canopy. In Nebraska, estimated yield losses are generally 20% or less in highly susceptible varieties. The source of this disease is infested soybean residue, infected seed, or airborne spores. This disease can overwinter on soybean residue in Nebraska. Symptoms of the disease are spots about ¼ inch in diameter with the center of the spot being gray to brown and having a reddish purple margin. Timely fungicide application at pod set can be very effective in controlling frogeye leaf spot in soybeans.
For more information and pictures of southern rust in corn and frogeye leaf spot in soybeans, please visit our local website at croptechcafe.org or give me a call at 727-2775. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.