Purdue News

May 31, 2006

Pathologist: So far, all's quiet on Midwestern soybean rust front

WEST LAFAYETTE, Ind. — Only time and weather patterns will tell whether Asian soybean rust moves into the Midwest this year and, so far, neither is talking, said Greg Shaner, Purdue University plant pathologist.

As much as agricultural researchers learned about the fungal disease in 2005, they still can't say if and when rust will infect the Corn Belt, Shaner said. He advised producers to keep a close eye on their fields and on weather reports this season. Growers also can stay up on rust's whereabouts through Purdue.

"We've had so little experience with this disease in the United States that it's really difficult to say what our risk for rust infection is in the Midwest," Shaner said.

"I think most people feel that here in the Corn Belt we're not likely to see rust before soybeans flower in late July and August, and probably even later than that. Rust might not occur until the beans are beginning to fill the pods. In any case, we need to remain vigilant until the beans are pretty well developed. Then, if rust doesn't appear until that stage, there probably wouldn't be enough time for it to do much damage."

In 2005 soybean rust confined its crop-infecting activities to the southern United States. Despite a record hurricane year that seemed primed to push rust into the nation's midsection, the disease never made its way above the Mason-Dixon Line.

Rust infection this year is following a similar pattern. To date, rust has been confirmed in Florida, Georgia, Alabama and the southern tip of Texas. The infected area in Texas and two others in Alabama and Georgia were destroyed.

"Right now rust isn't moving," Shaner said. "There have been no new rust findings since early March."

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.

Worrisome to researchers and farmers is how quickly and easily rust can spread. Rust pustules produce spores that start the infection process within days of landing on soybean leaves. One moderately infected soybean plant can produce about 6 million spores per day.

"The way this fungus gets from one place to another is by the wind carrying the spores," Shaner said. "We know from last year spores were carried into the Midwest and even into the northern Plains, but we didn't see rust in those areas."

Spores that traveled into Indiana and neighboring states likely hitched rides on hurricane remnants, Shaner said. Researchers don't know if those spores were viable when they arrived in the Midwest, leading some to wonder whether rust is a poor traveler.

"It is possible that even though the spores may be carried long distances they don't survive the flight," Shaner said. "If that's the case, then maybe our risk is considerably less than we'd originally thought based on what we know about rust on cereal crops and corn."

Purdue and sister land-grant universities across the country are prepared in case rust heads north.

"As we did last year we will again have what we call sentinel plots," Shaner said. "These are small plots of soybean that are planted throughout the state. We'll probably have about 23 of these sites."

Purdue researchers had hoped to plant sentinel plots earlier than most soybeans, so that rust might infect those plots first, Shaner said. However, a wet spring has interfered with early planting at some locations, he said.

Sentinel plots are intended to act as an early warning system, Shaner said.

"Once the beans in those sentinel plots begin flowering, which will be late June, cooperators will monitor those plots once a week," he said. "They will collect 100 leaves and send those by overnight mail here to Purdue, where those leaves will be examined under a microscope for any evidence of rust."

Should rust be confirmed on sentinel plots, farmers will be notified through various media outlets and Purdue information sources, including a toll-free rust hotline.

The hotline — (866) 458-RUST (7878) — features recorded rust updates from Shaner. Messages will be updated weekly, or more often if circumstances warrant.

Other Purdue soybean rust resources include:

• Purdue Agriculture Soybean Rust Web site — Contains Purdue-related soybean rust news and links.

• Purdue Plant and Pest Diagnostic Laboratory Soybean Rust Web site — Provides information on submitting soybean leaf samples to the laboratory, plant scouting, soybean rust host plants, fungicides and more.

• "Preparing for Asian Soybean Rust" — This Extension publication (ID-324) covers the basics about the fungal disease, how it spreads and control options. The publication can be downloaded online. Printed copies can be ordered online.

For additional information on soybean rust and where infection has been confirmed, visit the U.S. Department of Agriculture's rust observation Web site.

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 Department of Botany and Plant Pathology


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