Time and weather patterns will deterime whether Asian soybean rust moves into the Midwest this year. So far, things are quiet.
While researchers learned much about the fungal disease last year, they still can't say if or when rust could hit the Corn Belt, says Greg Shaner, Purdue University plant pathologist. He suggests that producers keep a close watch on their fields and weather reports. "We've had so little experience with this disease in the United States that it's difficult to say what our risk for rust infection is in the Midwest," says Shaner.

The general feeling is that rust isn't likely to enter the Corn Belt before soybeans flower in late July and August-- very possibly later than that. Regardless, producers need to remain vigilant until the beans are mostly developed. At that point, rust can't do too much damage.

Last year, soybean rust remained in the southern United States, despite a record hurricane year, which could have pushed it into the nation's midsection. The infection has followed a similar pattern this year. It's been confirmed in Florida, Georgia, Alabama and the southern tip of Texas. The infected areas in Texas and two others in Alabama and Georgia were destroyed. "Right now rust is not moving," says Shaner. "There have been no new 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 plant's ability to produce seeds. In extreme cases, the disease can wipe out 80 percent of a soybean field's yield potential.

It's a concern because of how quickly and easily rust can spread via the wind. Rust pustules produce spores that start the infection within days of landing on soybean leaves. One moderately infected soybean plant can produce about 6 million spores per day.

Last year rust spores were carried into the Midwest and the northern Plains, yet rust didn't develop. "It's possible that even though the spores may be carried long distances they don't survive the flight," notes Shaner. If that's true, the Midwest may face less risk than first thought.

Officials in Midwest states will continue to monitor sentinel plots as an early warning system. Should rust be confirmed on any sentinel plots, soybean growers will be notified. Many land-grant universities have soybean rust hotlines. For example, Purdue's is (866) 458-7878; a Web site is found at http://www.agriculture.purdue.edu/soybeanrust/.

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

Purdue University