Purdue News

October 26, 2006

Indiana case is northernmost advance of soybean rust

WEST LAFAYETTE, Ind. - Asian soybean rust has stretched its diseased arm farther north, with fungal infection found in Tippecanoe County, Ind.

The new case, detected in a soybean plot on a Purdue University research farm near Purdue's West Lafayette campus, is among six rust cases confirmed in the Hoosier state in the past week. Rust also was found in Knox, Pike, Posey, Vanderburgh and Warrick counties in southwest Indiana.

"We found rust in some late-maturing soybeans at Purdue's Agronomy Center for Research and Education (ACRE)," said Greg Shaner, Purdue Extension plant pathologist. "This is by far the northernmost find of soybean rust in the United States."

A rust pustule was spotted on one soybean leaf among 77 leaves collected Sunday (Oct. 22) at ACRE, Shaner said. ACRE is located about five miles northwest of West Lafayette.

"There's nothing significant about this location," Shaner said. "It just happens to be where we were looking."

The recent flurry of rust finds in Indiana, southern Illinois and western Kentucky provides valuable lessons for farmers and soybean researchers, Shaner said.

"What we've learned is that even without a tremendous amount of rust at the source, viable rust spores moved several hundred miles over a two- or three-day period," he said. "If this had happened earlier in the season when our soybeans were still green, I think we'd be seeing rust all over the place.

"This shows that if we know there's a lot of rust in Louisiana, Mississippi and Texas, and we have a weather pattern that brings air and rain our way, we need to be concerned."

Because most soybean crops in Indiana have been harvested or are harvest-mature, the disease poses no threat this season, Shaner said. If rust infection occurs when soybean leaves are still green, the disease can significantly reduce crop yields.

U.S. Department of Agriculture computer tracking models indicate rust moved into Indiana on storm systems that swept across the state Sept. 22-24. Those storms traveled up the Mississippi River valley from Louisiana and then turned east. Two years ago, Louisiana was the first state in the continental U.S. to report soybean rust.

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.

The rust fungus produces spores that are carried by wind to other soybean fields, kudzu patches and similar legumes. Rust needs green leaf tissue to remain viable, meaning it can survive the winter only on living host plants in the Deep South. Rust must then travel north from Gulf Coast states to infect Midwest soybean crops.

Farmers can control rust with properly timed fungicide applications. There are no rust-resistant soybean varieties.

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: Steve Leer, (765) 494-8415, sleer@purdue.edu

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

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

Note to Journalists: Other farm-related story ideas are available at Purdue Agriculture's Farming 2006 Web site

Related Web site:
Purdue University Department of Botany and Plant Pathology


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