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Soybean rust at Indiana border no reason for concern

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Written Friday, October 13, 2006  

Indiana soybean farmers have no reason for concern over this week's confirmed cases of Asian soybean rust in Kentucky and Illinois counties, said Greg Shaner, Purdue University Extension plant pathologist.

"There is no risk for this year's Indiana soybean crop," Shaner said. "There's very little green leaf material remaining for rust to infect. Even though rust made it into Kentucky and Illinois and rust spores might have gotten into Indiana doesn't mean anything for next season, either."

Soybean rust was confirmed in the western Kentucky counties of Caldwell, Christian, Fulton, Hopkins, Lyon, Marshall, Todd and Union, and Pope County in southern Illinois. The northernmost county on that list -- Union -- borders Posey County in southwest Indiana.

Soybean rust is a foliar disease caused by the fungus Phakopsora pachyrhizi. The fungus forms tan lesions on soybean leaves. Infected leaves die and fall off, severely limiting the soybean plant's ability to produce seeds. In extreme cases, the disease can wipe out 80 percent of a soybean field's yield potential.

Rust was first found in the continental United States in Louisiana in November 2004. Since that time the fungal disease has infected soybean crops mostly in the far South.

Fungal spores spread by wind and then infect soybeans, kudzu and similar legumes. The Union County, Ky., infection is believed to be the farthest north the disease has been found.

Working in Indiana's favor is soybean rust's inability to survive the winter, Shaner said. The disease needs green leaf tissue to remain viable. Most leaf tissue capable of allowing rust to overwinter is in Gulf Coast states, meaning that the disease must make the long journey north each year.

"Many of the soybeans here have already been harvested or are mature enough that no green leaves remain," Shaner said. "Even the kudzu we have in Indiana will die back in the winter, giving rust no overwintering host."

Although rust poses no threat in Indiana this year, farmers are encouraged to send suspicious soybean or kudzu leaves to Purdue's Plant and Pest Diagnostic Lab (P&PDL) for analysis, said Gail Ruhl, P&PDL co-director.

"Confirmation of rust in Indiana at this late date would still provide valuable information to scientists who are working on predictive models for this disease," Ruhl said.

The $11 P&PDL sample handling fee will be paid by funds provided by the Indiana Soybean Board and the National Plant Diagnostic Network, Ruhl said.

For more information about soybean rust, visit the P&PDL's soybean rust Web site at http://www.ppdl.purdue.edu/PPDL/soybean_rust.html or the U.S. Department of Agriculture's soybean rust monitoring home page at http://www.sbrusa.net/ .

Producers also can download or purchase Purdue Extension publication ID-324, "Preparing for Asian Soybean Rust." To download the publication, log onto http://www.ces.purdue.edu/extmedia/ID/ID-324.pdf . Single copies of the publication can be ordered for $2 or packages of 25 for $5 by logging onto https://secure.agriculture.purdue.edu/store/item.asp?itemID=16918 .

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