The report of soybean rust in Louisiana means Midwest farmers may have to deal with the problem next growing season if the right mix of plant hosts and weather develops, according to Purdue University experts.

"We don't yet know how widespread the infection is, but if you find it in one location, it's likely that it's also on other nearby spots that you've not yet detected," says Ray Martyn, a professor and head of the Department of Botany and Plant Pathology. "If it's not controlled in Louisiana, then it could be a problem for Indiana farmers next summer."

Martyn was part of a team of Purdue researchers that plotted the potential rate for soybean rust spread in the U.S. The work was done under contract for the USDA as part of a pathway analysis to help identify areas of susceptibility and where more research was needed.

Martyn says soybean rust could easily make the trek from the southern states to the Midwest during the next growing season if conditions are favorable.

The fungus, reported Wednesday (Nov. 10) for the first time in this country, could survive the winter if it finds one of 40 known hosts for the disease. Kudzu, a common nuisance plant in the South, is one of those possible hosts.

"If a plant stays moderately green all winter and it's a host for the disease, then soybean rust could overwinter in the extreme southern parts of the U.S.," Martyn says.

Even if soybean rust takes up permanent residence in this country, it also needs favorable growing conditions to spread. "It needs humidity and moderate temperatures," Martyn says.

Greg Shaner, a professor of botany and plant pathology who also worked on the pathway analysis, says the spring and summer southerly breezes could easily transport soybean rust spores from state to state as the growing season progresses.

There are no soybean varieties grown in the U.S. that are resistant to soybean rust, so using fungicides is the only control measure currently available to U.S. producers. That could pose a problem next year if the disease spread is prevalent and fungicide supplies are low.

More information on soybean rust is available at www.agriculture.purdue.edu/soybeanrust or at www.ppdl.purdue.edu/ppdl/soybean_rust.html .