The first report of soybean rust (SBR) in Arkansas was confirmed near Halley, AR (Desha Co.) on August 7th. This is the same county SBR was first detected in 2012. SBR has also been confirmed in Limestone Co., Alabama which neighbors Giles Co., Tennessee.
No SBR has been found in Tennessee in 2013 as of today. Leaves from a soybean sentinel plot 1 mile north of the Alabama-Tennessee border in Giles County have all been negative for SBR, including samples taken this past Monday. Other southern Tennessee counties that have been scouted for SBR and all have been negative this season include, Franklin, Shelby, and Fayette. These sentinel plots and others across the state will continue to be monitored for SBR. Updates will be posted on http://NewsUTcrops.com, http://sbr.ipmpipe.org, and the UT Rust Hot Line (1-877-875-2326).
Soybeans at growth stage R5 (beginning seed) and later are unlikely to benefit from a fungicide application in the season now, unless there is prevalent disease in the field and/or they are being grown for seed. Later planted soybeans and those planted behind wheat will most likely benefit from at least 1 fungicide application with the wet, humid weather in Tennessee and the increased threat of SBR this year. The fungicide efficacy table found at UTcrops.com (Soybean-> Diseases and Nematodes -> Fungicide Table – 2013) can be used to identify fungicides that will provide control for SBR as well as other diseases. For management of SBR, fungicides in both strobilurin and triazole group can be effective, but they affect the fungus differently. Strobilurin (or QoI) fungicides have the ability to inhibt both spore germination and host penetration, but have little or no effect once the fungus has penetrated or colonized leaf tissue; hence they are most effective if applied prior to infection. Triazoles have the ability to inhibit or stop development of infection that have already established at low levels, but have little or no effect on spore germination; hence they are the fungicide of choice if it is known SBR is established at low levels in a field along with a strobilurin to control further infection by spores. More information on SBR can be found in the Soybean Rust Compendium and UTcrops.com.
If you have any questions or concerns please contact your local county agent or myself (youngkelly@utk.edu, 731-425-4713).
