By DOUG SCHMITZ
Iowa Correspondent

DES MOINES, Iowa — After nearly three months of extensive analysis, state agriculture officials confirmed an infected leaf found with dead spores in a Mahaska County storage bin shows no further signs of Asian soybean rust, and likely originated outside of Iowa.

“We did verify that one leaf submitted in a plant sample was infected with Asian soybean rust, but how it got into Iowa still needs to be determined,” Bill Northey, Iowa Agriculture Secretary and Iowa State University (ISU) officials announced on May 21.
“After careful examination of the materials collected to date,” he said, “we believe no Asian soybean rust infection occurred during the 2006 growing season in Iowa.”
Investigation

The plant pathogen found in Iowa made national headlines when the single leaf was reportedly discovered in a storage bin from soybeans harvested in 2006. ISU testing on March 12 revealed the sample was contaminated with Asian soybean rust.

The sample, offered on Jan. 15 by an individual whose name the USDA said it was unable to disclose for legal reasons, was submitted to ISU’s Plant Disease Clinic on March 8, with additional testing conducted by the USDA Asian soybean rust identification laboratory in Beltsville, Md., Michigan State University and ISU.
On March 13, the Iowa Department of Agriculture and Land Stewardship (IDALS) and ISU collected additional samples of seed and plant materials from bins at the location, as well as adjacent fields to where the sample was allegedly found. While many leaves had shown early signs of frogeye leaf spot, the USDA said it ruled out Asian soybean rust.

In March, the Iowa Soybean Rust Team – which includes personnel from the IDALS, ISU, the Iowa Soybean Assoc. (ISA) and the USDA Animal and Plant Health Inspection Service in Ames – said the infected leaf didn’t pose a threat to the 2007 growing season because the fungus and spores that cause the disease cannot live through an Iowa winter, especially since they need the green-leaf tissue to survive.

“We are very pleased that Asian soybean rust did not reach Iowa soybean fields as was originally reported,” said David Wright, ISA director of contract research and a member of the Iowa Soybean Rust Team.

Since the team has been carefully monitoring the movement of soybean rust for the past two years, Wright said it was doubtful the disease had formed in Iowa, which is the nation’s leading soybean producer.

“We believed all along that the rust-infected leaf delivered to Iowa State University’s plant diagnostic clinic likely did not originate in Iowa,” said Wright, who is also coordinator of the North Central Soybean Research Program in Urbandale, Iowa – which comprises the state soybean checkoff boards of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin.

“However, no one knows exactly where the leaf originated or why the individual delivered it to the diagnostic clinic,” he said. “An ongoing federal investigation hopes to answer those questions.”

Early detection

Asian soybean rust was first reported in the continental United States in Louisiana after the hurricane season in 2004, on living green tissue at the end of growing season, although the first recorded contamination occurred in Brazil in 2002.

ISU plant pathologists said they think the disease entered the U.S. on winds from the south.

Although the disease has been found as far north as Illinois and Indiana, so far this year, the number of positive finds for rust are eight counties in Florida; five counties in both Alabama and Georgia; and one county in Texas.

State officials said soybean producers need to continue to be vigilant and monitor conditions that favor rust, consult with their respective county ISU extension specialists on identification and management plans and work with the Iowa Soybean Rust Team’s First Detectors to positively identify any suspected soybean rust in their fields.

From 2004-06, the team recruited and trained “First Detectors,” made up of more than 600 agribusiness professionals around Iowa who examine leaf samples and decide whether they warrant further analysis by ISU extension personnel or faculty scientists to detect possible infection.

The Soybean Checkoff continues to provide partial funding of the Sentinel Plot System, a nationwide collaboration among USDA, land grant universities and soybean producers to monitor the over-wintering and spread the disease throughout the United States.

Wright said part of this system utilizes computer models that look at weather data and wind currents to predict where soybean rust will likely show up first, which is why the report of soybean rust last year didn’t make sense to him, based on the available data. But Wright cautioned that “just because rust did not make it to Iowa in 2006 doesn’t mean soybean producers won’t experience it in future years. It is just a matter of time; rust was confirmed in Illinois and Indiana during the 2006 growing season.”

ISU has planted 20 sentinel plots around Iowa. Since the plots are monitored throughout the season, producers will be informed of any threat.

In the end, IDALS and ISU officials said the origin of the infected leaf required further investigation by the Office of Inspector General, the investigative arm of USDA. “We take the discovery of any new plant pathogen very seriously, especially one that would be the first recorded occurrence in Iowa,” Northey said.

Paul Feeney of the Office of the Inspector General said it couldn’t comment on the investigation, due to departmental policy.
USDA encourages producers to consult with Iowa Soybean Rust Team First Detectors if they suspect plants might have soybean rust. There is no charge, and names and contact information are available at www.soybeanrust.info and at county extension offices.