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Asian soybean rust confirmed on Iowa soybean plant tissue

Asian soybean rust was conclusively identified on soybean plant tissue submitted to the Iowa Soybean Rust Team last week.

The soybean residue is reported to have been recovered from a bin of soybeans produced in Iowa in 2006. Efforts are underway to identify other remnant plant residue that may show symptoms and signs of the disease in order to discern details of this event. Asian soybean rust has never been identified in an Iowa field since the disease was reported in the continental United States in November 2004.

The rust was tentatively identified by the Iowa State University diagnostic lab, then sent for positive confirmation to the USDA laboratory in Beltsville, Maryland, where all first finds in a state must be confirmed. The scientists there said it looked like soybean rust upon visual examination. Testerday, the word came that molecular testing confirmed the pathogen, said Greg Tylka, Iowa State University Extension plant pathologist and spokesperson for the Iowa Soybean Rust Team.

The soybeans were harvested in Mahaska County in southeast Iowa, Tylka said, two counties southeast of Des Moines. The field had low-productivity during the season, he said, and a sample was the lab in October, but no leaves were present on the dead tissue and rust was not detected.

The grower then found one leaf in the bin of the harvested grain and passed it on to a crop consultant to see if it could possibly have rust. The consultant sent it to the Iowa team last week.

"It was just a fluke," Tylka said. "We were just lucky" that one leaf would surface at this time when there was no known soybean rust active for hundreds of miles around last season. ISU had soybean rust sentinel plots two counties east of Mahaska, he said, but no rust was found there or anywhere else in the state.

In a news release this afternoon, ISU officials said efforts are underway to identify other remnant plant residue that may show symptoms and signs of the disease in order to discern details of this event, according to the Iowa State news release.

The fungus and the spores that cause the disease cannot survive without green leaf tissue and will die during Iowa winters. The recently discovered rust fungus does not pose a risk of infection for the 2007 growing season in Iowa.

"The fast, conclusive identification of soybean rust in this one particular plant residue sample illustrates the rapid diagnostic capabilities available at Iowa State University to protect the state's soybean crop from the threat of this disease," said Iowa State University College of Agriculture Dean Wendy Wintersteen.

"This discovery reminds us that it is possible for Iowa fields to become infected with this disease," said David Wright, director of contract research at the Iowa Soybean Association. "Nonetheless, growers should not overreact to this development. Instead, growers must be ready to act appropriately and economically in 2007 should this disease again show up in Iowa and be a threat to soybean yields."

Bill Northey, Secretary of Agriculture with the Iowa Department of Agriculture and Land Stewardship, said the finding does not necessarily increase the risk for next year's crop.

"The confirmation of this disease in the 2006 crop does not guarantee that we will have Asian soybean rust in the 2007 Iowa soybean crop. As in previous years, producers should monitor conditions that favor rust and consult with extension specialists on identification and management plans," Northey said. "However, it is imperative for producers to avoid the inclination to panic and take drastic, costly and unnecessary action before positively identifying soybean rust in their fields."

Tylka said the two things that most interested him are that it was there in the field and no one detected it during the season, and that the infection was so far away from any other soybean rust found last year.

"It was in the middle of nowhere," he said.

The Iowa Soybean Rust Team comprises personnel from Iowa State University College of Agriculture and ISU Extension, the Iowa Soybean Association, the Iowa Department of Agriculture and Land Stewardship and the USDA Animal and Plant Health Inspection Service. The team recruited and trained more than 600 agribusiness professionals from 2004 to 2006 to serve as "First Detectors" who can examine leaf samples and decide whether the samples warrant further investigation for possible infection with soybean rust by ISU Extension personnel in the state or by campus-based ISU scientists.

Growers are encouraged to consult with Iowa Soybean Rust Team First Detectors in the 2007 growing season if they observe plants that they suspect might have soybean rust. There is no charge to consult with these First Detectors concerning possible soybean rust infections.

Asian soybean rust was conclusively identified on soybean plant tissue submitted to the Iowa Soybean Rust Team last week.

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