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College of Food, Agricultural, and Environmental Sciences


Season Remainder Remote for Soybean Rust

August 18, 2005

Editor's note: This is part of a periodic series on information regarding soybean rust. The goal is to provide media with the latest updates on the disease and Ohio State's role in research and education. These updates are expected to continue throughout 2005.

WOOSTER, Ohio — Worries over soybean rust are now behind Ohio growers.

Evaluations of Ohio's 45 sentinel plots two weeks after remnants from Hurricane Dennis dumped rains through the Midwest in July have found no hints of soybean rust infections. Ohio State University Extension educators will scout the plots one final time for any spores that would have ridden on the coattails of the storm system before declaring Ohio officially out of the woods.

"Is there a chance that we might still get some soybean rust in Ohio? It's possible. If we were to get disease buildup in other parts of the country, we get a late hurricane, say in September, and we have a lot of late-season beans, there might be a chance," said Anne Dorrance, an OSU Extension plant pathologist and the state's leading soybean rust researcher. "Would we need to spray in that situation? It's very unlikely because there won't be enough time between then and maturity. Inoculum would be so low and soybeans are already at the R3-R6 stages that it wouldn't impact yields anyway."

The furthest north that soybean rust has been reported in growers' soybean fields so far this growing season is Georgia and Alabama, with storm systems from Florida to blame for spreading spores. Soybean rust has also been found in Mississippi, and reports of soybean rust finds are expected to continue in infected states throughout the season, according to the U.S. Department of Agriculture.

"It took a very long time to build up enough inoculum for it to finally be found in growers' fields, and even in the fields it's been found in, it's been in very localized areas," said Dorrance, a researcher with Ohio State's Ohio Agricultural Research and Development Center. "At this point it would take a lot of inoculum to infect a lot of soybean leaves, which have to build up to a large number of spores to spread infections before it can even begin to reach southern Ohio. And that possibility is remote."

Dorrance said that specialists nationwide will continue to monitor sentinel plots throughout the winter to determine survivability of soybean rust spores.

"We need to focus on managing this disease and avoiding this bridge from the fall to the next spring so that we always have low levels of inoculum at the beginning of each season," said Dorrance. "Hopefully the cold winters will help us do that." Research has shown that soybean rust cannot survive in cold temperatures, which makes the disease's life in Ohio — even if found late in the season — short lived.

Soybean rust is an aggressive fungus caused by either of two fungal species, Phakopsora pachyrhizi, also known as the Asian species, and Phakopsora meibomiae, the New World species. The Asian species, the one found in the United States, is the more aggressive of the two species, causing more damage to soybean plants.

Last year the disease was identified in eight states, spreading as far north and west as Missouri.

For the latest in soybean rust development, log on to USDA's soybean rust monitoring Web site at For additional information on soybean rust, log on to Ohio State's Agronomic Crops Network Web site at

Candace Pollock
Anne Dorrance