Experts with University of Tennessee Extension today confirmed the presence of a significant agricultural disease in the state. Asian soybean rust was found in West Tennessee on soybean leaf samples taken from several fields in Gibson, Obion and Weakley counties on Thursday, October 12.

The confirmation came at the end of the growing season when most soybeans had been harvested. UT Extension plant pathologist Beth Long says the disease caused no damage to Tennessee’s soybean crop this year.

Because soybean rust is spread primarily by wind-borne spores and is capable of being transported over long distances, no regulatory action will be taken. Growers should contact their local county UT Extension agent to discuss preventative and control measures for next year.

The disease samples - a few rust pustules - were found on soybean leaves and visually identified with a microscope at the UT Extension lab at Jackson. The samples were then tested with the “QuickStix” method by Dr.
Melvin Newman, Department of Entomology and Plant Pathology in Jackson.
Final confirmation that the pustules were Asian soybean rust was determined by polymerase chain reaction (PCR) testing in Dr. Kurt Lamour’s lab at UT Institute of Agriculture in Knoxville.

After the soybean plants were sampled, a hard frost occurred in West Tennessee, and most remaining green leaf tissue was destroyed. Soybean rust can not survive the winter in Tennessee, but rust spores can easily be blown in during the growing season from areas in the Southern U.S. where freezing temperatures do not occur.

Asian soybean rust is caused by the fungal species Phakopsora pachyrhizi and is known to infect kudzu and many other legume species. It has the potential to significantly reduce soybean yields but can be managed with the use of fungicides if detected early. At this time there are no commercial soybean varieties resistant to soybean rust. Prevention and control measures are expected to raise costs for producers and ultimately for consumers. Fungicide applications can reduce yield losses from rust and other late-season diseases, depending on the plants’ developmental stage, the time during the growing season when soybean rust is detected and weather conditions.

Soybeans rank among the state’s top crops, earning farmers approximately $232 million in cash receipts in 2005. In March, the Tennessee Agricultural Statistics Service reported that state producers intended to plant some 1.22 million acres of soybeans.

UT Extension monitored for rust in soybean sentinel plots and spore traps across the state all summer and only found these few rust lesions on soybean leaves last week. Dr. Newman speculates that the lack of rain in West Tennessee during critical times in the growing season prevented soybean rust from developing earlier. “Several rain fronts passed by West Tennessee, but they developed and caused rain in Western Kentucky. This may be why soybean rust was recently found in 13 western Kentucky counties while none was found in Tennessee until last week,” he said.

In addition to these three West Tennessee sites, Asian soybean rust has been found infecting this year's soybeans in 11 states. Including reports of rust on kudzu, a total of 141 counties in 11 other states identified rust this year: 13 in Alabama; 18 in Florida; 21 in South Carolina; 24 in Louisiana; 15 in Georgia; 4 in Texas; 3 in Mississippi; 22 in North Carolina; 13 in Kentucky; 6 in Illinois; and 2 in Missouri.

More information about soybean rust and recommended measures for controlling the disease are available through the UT Extension Web site: http://UTcrops.com. First click on “soybean” then follow the link labeled “diseases and nematodes.”

Growers can also visit the USDA soybean rust Web site: http://www.sbrusa.net/ and view the map showing positive locations.

UT Extension offices are listed in local phone books under the county government listing. Additional information is available online at: http://www.utextension.utk.edu/offices

This is the first instance of Asian soybean rust found in Tennessee during 2006. There were no finds of this disease during the 2005 growing season.
Asian soybean rust was first found in the United States in November 2004.
The disease was confirmed at that time in samples across nine southern states, including one sample from Shelby County, Tennessee.

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