KNOXVILLE, Tenn. — This growing season was tough enough for Tennessee farmers, but earlier this month soybean producers got the news that Asian soybean rust (ASR) had made its way into West Tennessee on soybean leaf samples.

The samples were collected by Dr. Angela Thompson, University of Tennessee (UT) Extension soybean specialist, from a field plot in Gibson County at the UT Milan Research and Education Center on Oct. 3.

While always a concern, especially in a year plagued with a hard spring freeze and record heat and drought, UT Extension plant pathologist Beth Long said the disease caused no damage to Tennessee’s soybean crop this year mostly due to the fact that the majority of the soybean bean crop had been harvested and little green leaf tissue remains in the field.

In a state where soybeans have ranked among the state’s top crops, earning farmers approximately $278 million in cash receipts in 2006. Producers here, as in many drought-stricken states, have not fared as well recently seeing a significantly diminished crop for 2007.

Yields are down from 39 bushels per harvested acre in 2006 to estimates of just 24 bushels per acre this year. The Tennessee Agricultural Statistics Service reported in September that production for this year was expected to fall by 57 percent from last year’s 44 million bushels to just 25.2 million bushels.

Dr. Melvin Newman, UT Department of Entomology and Plant Pathology, in Jackson, speculates that the lack of rain in western 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 west of the Mississippi River. This may be why soybean rust was found in Eastern Arkansas in late September,” he said.

ASR has also been found in other neighboring states including Alabama, Mississippi and Kentucky.

Don Hershman, Extension Plant Pathologist for the University of Kentucky said the season’s early freeze actually could have helped that state’s soybean situation and ASR was a matter of too little too late to be a factor.

“With soybean rust showing up so early in the season in Texas and Louisiana, we seemed to be set up for a possible disease problem in Kentucky. As it turns out, we dodged another bullet, and rust did not show up until very late in the season. The spring freeze that occurred in early April probably saved us as much as anything. It took out a lot of kudzu, much of which had actively developed soybean rust,” said Hershman. “The levels of the fungus never really recovered until late summer. The drought conditions in much of Alabama, Georgia and Mississippi also greatly reduced our risk.” While producers may have dodged a bullet, Hershman warns against complacency.

“I have heard several people say that it is apparent that soybean rust is not going to be the serious disease threat in the U.S. that it is in Brazil and other countries. I say, it is way too early to say that. We certainly cannot afford to put our guard down for 2008. Only time will tell what the true potential for soybean rust is in the U.S. But for now, we must remain vigilant,” he said.

No regulatory action will be taken because soybean rust is spread primarily by wind-borne spores and is capable of being transported over long distances. Also, the disease cannot survive the winter in Tennessee and Kentucky, but rust spores can be blown in during the growing season from areas in the Southern United States where freezing temperatures do not occur.

The early October finding was the first instance of ASR found in Tennessee during this year, however it was found in western and middle Tennessee during late October 2006, immediately before a heavy frost. There were no finds of this disease during the 2005 growing season.

ASR first showed up in the United States in November 2004 when it was confirmed in samples across nine southern states, including one sample from Shelby County, Tenn.

To date, in addition to the western Tennessee site, ASR has been found in 15 states and a total of 169 counties.

There are currently no commercial soybean varieties resistant to the disease which could mean an increase in costs for producers and ultimately for consumers due to prevention and control measures. Fungicide applications can reduce yield losses from rust and other late-season diseases, depending on the plants’ developmental stage.

More information about soybean rust and recommended measures for controlling the disease are available through the UT Extension website at http://UT crops.com

First click on soybean then follow the link labeled diseases and nematodes.

Growers can also visit the USDA soybean rust website at www.sbrusa.net and view the map showing positive locations.