For rust outbreaks: ASR model points toward Southeast

Joe Russo wasn't surprised when Asian soybean rust showed up in sentinel plots in southeast Mississippi, south Alabama, the Florida Panhandle and south central Georgia in mid-July.

Russo, president of ZedX, Inc., an information technology company based in Pennsylvania, expected rust to be found in those areas because that's where the computer model he helped design indicated the disease would most likely occur after Hurricane Dennis came ashore on the Florida coast July 11.

“The model was showing an intense area of deposition of rust spores where researchers and Extension specialists should be looking,” said Russo. “The area began in South Carolina and ran down through Georgia, Alabama and into the east side of Mississippi.” (Rust was found in George County in southeast Mississippi; Baldwin County in south Alabama; Escambia County in the Florida Panhandle and Tift County in south Georgia.)

Russo discussed the development of the model and its workings during a session at the InfoAg 2005 Information Agriculture Conference in Springfield, Ill., on July 20.

At that time, the model was indicating that the area with the highest probability of Asian soybean rust for the following days was in south Georgia. Soybean rust was confirmed on two leaves of soybeans in a sentinel plot in Colquitt County in southwest Georgia July 26.

“By July 12, Hurricane Dennis was moving over Illinois,” said Glenn Hartman, a plant pathologist with the USDA's Agricultural Research Service at Champagne-Urbana, Ill. “The winds swirling around the center of the storm brought spores into Ohio, but the most deposition that day occurred in Georgia.

“We were seeing similar deposition at the beginning of this week (July 18),” said Hartman, who followed Russo on the program at the InfoAg meeting in Springfield. “By July 26, this part of Georgia could have a lot of rust.”

Both scientists couched their assessments in those terms because forecasting outbreaks of Asian soybean rust in the United States is still very much a work in progress. Although winds can carry rust spores over long distances, researchers have found conditions not conducive for rust development in much of the Soybean Belt this summer.

“This model is very proactive,” said Hartman. “It's changing all the time because of all the real-time information that is being fed into it. But it was right on with the infection in Georgia.”

Fortunately for U.S. growers, another hurricane, Ivan, provided a sneak preview of Asian soybean rust last year. Ivan took spores from rust-infested areas south of the equator and carried them to an area from South Carolina to Louisiana where rust was first discovered in a U.S. field near Baton Rouge on Nov. 8.

During the winter months, USDA began developing a comprehensive response to the threat that Asian soybean rust would either overwinter in the Deep South or be brought back to the United States by another tropical storm. Russo and his company helped put together a system for tracking soybean rust.

This spring, USDA launched a new Web site, located at, that tracks the appearance and movement of Asian soybean rust. One of its key features is a U.S. map that shows areas that are being scouted for soybean rust in green. Red denotes areas that have been confirmed to have Asian soybean rust.

“This is a three dimensional model,” said Russo. “It provides a weather-based assessment of likely atmospheric pathways, regions of deposition and the timing of aerial transport of soybean rust from current source regions in South America and Africa to North America.”

The Web site also provides commentary and narrative updates by state Extension specialists about local pest observations, crop stage, scouting dates and techniques and management recommendations. It also allows users to sign up for soybean rust alerts.

On July 27, for example, the Web site contained information that a cold front stretching from northeast Texas, through Arkansas, western Kentucky, southern Ohio, central Pennsylvania and New York, was likely to become stationary the weekend of July 30.

“The southerly movement of the frontal boundary will limit spore transport to just a few areas in the southeastern United States,” it said. “The soybean rust model predicts only light, local spore depositions in parts of Alabama and Georgia over the next few days, with some minor spread into the Carolinas over the weekend.”

The USDA system also receives reports from 700 soybean sentinel plots that were established by state Extension specialists across the Soybean Belt last spring. Information from the sentinel plots is fed into the computer model weekly or more often, if needed.

The Web site contains a series of other Web sites that provide different types of information on the potential outbreaks of soybean rust.

“The researchers have the richest site,” says Russo. “They see a national commentary on what's going on out in the field. After the researchers look at it and comment on the material, the information moves to the public site.”

Besides being a repository for almost all of the data generated on Asian soybean rust in the United States, the model also helps pinpoint areas where soybean specialists should concentrate their searches for rust through a “scouting algorithm” developed by USDA, Extension Service and ZedX personnel.

In the July 27 update, the Web site said that mobile teams, in conjunction with state and Extension personnel, were continuing to search for new soybean rust infections in the southeastern United States.

Hartman said Illinois farmers may not have to maintain their vigil for Asian soybean rust much longer in 2005.

e-mail: [email protected]

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