Soybean rust has not been detected infecting soybeans or kudzu in Tennessee as of this date. However, extremely small amounts of soybean rust have been confirmed in several counties in central Mississippi and some in Alabama and Arkansas. This is in the delta about 60 to 70 miles from the border of Tennessee. The amount of rust found was small but active. We are continuing to monitor for soybean rust in 12 soybean sentinel plot locations across Tennessee.
Recently, weather conditions have changed to a level that is conducive for rust development and spread in West Tennessee and to some extent into Middle Tennessee. However, data has shown that it could take 30 or more days of favorable weather to cause any yield damage. Tropical Storm Isaac is predicted to bring rain to the mid-south starting this Thursday and Friday (http://www.nhc.noaa.gov/TS-Isaac).
Producers should monitor their later soybeans for possible rust infections especially those fields that are still in good condition after the dry weather. Soybeans that have already reached the “R5” growth stage (seed 1/8 inch long in any pod on any of the top 4 nodes) will probably not have a yield reduction this late in the growing season even if soybean rust develops over the next few weeks. The national rust web site (www.sbrusa.net) is the best place to check on where soybean rust has been found or just call the UT Rust Hot Line (1-877-875-2326) any time for a free one minute update. Your local county Extension leader will also be able to help you identify soybean rust.
We are not recommending spraying for rust at this time but producers should keep alert and report to their County Agent any possible rust infections. If weather conditions remain favorable and rust spreads into Tennessee, recommendations may be made to spray a Triazole or Triazole + Strobilurin fungicide under certain conditions where soybeans are still able to produce a potential yield of at least 30 bushels/acre and are still in a growth stage between R1 and R5. Most soybeans are already passed this stage and will probably not be harmed by a rust infection this late in the growing season. Some soybean fields may be affected so severely by the dry weather that it would not be economical to add the expense of a fungicide application. Producers who have already sprayed with a fungicide (Triazole or a mixture of Triazole + Strobilurin) for other diseases may still have some protection from rust infection if it has not been over 2 or 3 weeks since they sprayed.
