Purdue News

October 18, 2006

Indiana rust occurrence too late to injure 2006 soybean crop

WEST LAFAYETTE, Ind. — Asian soybean rust has been found in Indiana for the first time, but it poses no threat to Indiana soybean producers this year, said a Purdue University expert.

Because more than 90 percent of Indiana soybeans already have been harvested or have at least reached maturity, there isn't much green, leafy plant tissue remaining for rust to infect, said Greg Shaner, an Extension plant pathologist.

"The soybean rust fungus only survives on living host plants, so here in the temperate region where we have winter and killing frost, it will be eradicated," he said. "So the soybean rust fungus will only survive in North America in the far South — Florida, perhaps along the Gulf Coast and maybe northeastern Mexico. It just depends on how far south the frost extends."

In order for soybean rust to return to the Midwest, the spores would need to build up again in regions where no killing frost existed, then winds would have to carry these spores northward, Shaner said. That means spores are no more likely to return next year than they were before the find.

The latest instances of soybean rust were confirmed Wednesday (Oct. 18) by the U.S. Department of Agriculture from fields of double-crop soybeans in Knox and Posey counties. This find most likely originated from the same introduction of spores that infected several counties in western Kentucky and southeastern Illinois.

For Indiana soybean producers, confirmation of the fungus this year means that if soybean rust returns to the Midwest in future growing seasons, the identification process will move much more quickly.

The federal government asks that when a state finds soybean rust for the first time, plant samples be sent to a lab in Beltsville, Md., for confirmation. After this one-time process is completed, state officials can independently diagnose future finds and immediately get word out to growers, Shaner said.

From this latest confirmation, researchers were able to learn more about how soybean rust spreads.

"Perhaps the most important thing we have learned from the appearance of soybean rust in Kentucky, Illinois and Indiana is that southerly winds can carry spores long distances," Shaner said. "Winds carried these spores more than 500 miles before they landed, and these were still viable after the long journey."

For more information on soybean rust, visit the Purdue Plant and Pest Diagnostic Lab Web site or call the Purdue soybean rust hotline at (866) 458-RUST (7878).

Writer: Jennifer Stewart, (765) 494-6682, jsstewar@purdue.edu

Source: Greg Shaner, (765) 494-4651, shanerg@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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