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Asian soybean rust is in west Kentucky
By TIM THORNBERRY
Kentucky Correspondent

PRINCETON, Ky. — The bad news is, Asian soybean rust (SBR) has been detected in western Kentucky; the good news is, it’s too late in the season for it to damage the 2006 crop.

As state agriculture officials see it, the much-anticipated arrival of the fungus couldn’t have come at a better time. Most of Kentucky’s soybean crop has passed the point of being affected, plus the area received its first frost of the year, which kills the disease.

The USDA’s National Agriculture Library reports that soybean rust is caused by either of two fungal species, Phakopsora pachyrhizi, also known as the Asian species, and Phakopsora meibomiae, the New World species.

The Asian species, the more aggressive of the two, causes more damage to soybean plants. The disease is spread primarily by wind-borne spores capable of being transported over long distances and can be devastating to soybean crops.

University of Kentucky (UK) Extension Plant Pathologist Don Hershman reported more than a week ago that the first signs of the disease showed up in a corner of an otherwise mature sentinel plot located at the UK Research and Education Center in Princeton but was soon found in other areas.

“Soybean rust was detected on soybeans for the first time ever in Kentucky on Friday, Oct. 6, 2006. Then between Sunday, Oct. 8 and Tuesday, Oct. 10, SBR was detected at various levels in six additional counties; Christian, Hopkins, Lyon, Marshall, Todd, and Union counties,” said Hershman.

Since then, three other counties have reported SBR in their areas; Fulton, Trigg and Webster counties were added to the list as of Oct. 13.

According to the USDA and adding reports on kudzu, there are a total of 123 counties in 10 states with rust this year including 13 in Alabama; 18 in Florida and South Carolina; 24 in Louisiana; 15 in Georgia; three in Texas and Mississippi; 17 in North Carolina; 10 in Kentucky and two in Illinois.

Even though Kentucky dodged a bullet, as far as rust damage is concerned, officials are keeping a close watch on crops that haven’t been harvested.

“For all finds, the stage of pustules was mostly uniform. This suggests to me that a large number of spores blew in sometime over the past two weeks and cut a pretty large swath in west Kentucky,” Hershman said.

“We are in the process of looking to the west and east to see if an even larger area of spore deposition and infection may have occurred. (SBR) simply cannot survive this far north. However, these finds are of great importance to the soybean rust predictive models. I am hoping to find a location that has decent infection that would provide for an educational opportunity or two.”

Rankin Powell is the UK Extension agent in Union County and said the soybean crop in his area is safe, at least for this year.

“We’re fortunate it came late and won’t hurt anything. We had a frost and that takes care of the rust plus the beans were so mature that it won’t be a factor this year,” he said. “It doesn’t overwinter, but we do know if the conditions are right, it will get here. The last two years have been dry in the south and southwest and it hasn’t had a chance to grow and get here earlier. Next year if the season is different it could do a lot of damage if it gets here early enough.”

Powell warned that even though farmers won’t have a concern for this year, they shouldn’t let their guard down.

“I’m afraid our growers may get complacent and it will sneak up on them. We’ll be watching early plots but it’s not easy to find. You have to scout for it. It’s a never-ending thing to keep an eye out for it,” said Powell.

Hershman said the finds, were in mobile plots except for the Caldwell and Union County discoveries, which were in sentinel plots.

David Lanclos, extension soybean specialist at Louisiana State University reported on the LSU website that “in managing soybean rust, the use of ‘sentinel plots’ will play a large role in providing information on the spread of the disease. The objective of sentinel plots is to have a crop in the field well ahead of the traditional crop, thus acting as a ‘trap’ crop for the spores. If rust is detected in the sentinel plots, this will allow proper production decisions on a regional and statewide basis to be made.”

Lanclos also said sentinel plots are used to track the spread of the disease and are also used in South America and other parts of the world to aid computer models in an attempt to predict where the disease may spread.

SBR had been found in all major soybean growing areas of the world except the United States until its discovery in November 2004. The disease is believed to have been blown in by hurricane winds and poses no threat to humans, but it can potentially wipe out soybean crops.

Since its discovery in the United States, crop and disease specialists across the soybean growing region have worked to understand how the disease develops and its impact on the crop as well as educating producers and others about the disease and its threat.

“The bottom line is this: the soybean rust finds will not impact soybeans in Kentucky or the U.S. this year,” Hershman said. “But, they will help us to refine soybean rust predictive models, which will help greatly with soybean rust management in future crops.”

For details about soybean rust or up-to-date information visit www.sbrusa.net or call 888-321-6771.

This farm news was published in the Oct. 18, 2006 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.

10/18/2006