Soybean Rust Bears Watching in '07

Developments in Louisiana are ones to watch.

Published on: Dec 20, 2006

Asian soybean rust made it into Indiana this past October. Greg Shaner, Purdue University disease specialist, found it in Tippecanoe County, in the form of spores. Other official sightings were reported in some southern Indiana counties, in southern Illinois and in Kentucky.

The gaps from southern Indiana to Tippecanoe County are likely because people weren't looking. It doesn't necessarily mean spores weren't in those locations. Since it was so late in the season, there was no concern that the disease would develop and cause problems.

"All that it really proved is that the spores can travel this far north," says Shaner. Asian Rust spores were not detected inside Indiana borders in '05.

The disease has been ballyhooed as a significant threat to soybean growers since the fall of '04, when spores were found in the deep South. That meant the disease had finally arrived in the U.S. from Brazil. It has been a concern and threat in parts of Brazil in South America now for several seasons. Much of what disease and Extension specialists are learning about monitoring for and controlling the disease is based on what has worked and not worked in Brazil.

Will the disease arrive in Indiana in '07 in time to be a threat? That's a question that's impossible to answer, Shaner says. However, he believes the key area to watch will be what happens in Louisiana and eastern Texas over winter and into spring. The rust spores survive on kudzu and other host plants, but can't survive in the Midwest during the winter due to cold temperatures and a lack of green vegetation.

Based on air circulation patterns monitored over the past two years, Shaner believes that if spores arrive into Indiana, they will come from the Louisiana/east Texas area. He doesn't see the discovery of spores or active disease in other more eastern parts of the South, such as Georgia, to hold much implication for what might occur in Indiana.

He's basing his expectations upon prevailing wind patterns. Weather models exist that allow weather forecasters and agronomists to predict which way spores could be carried across the country.

"The other thing that you need is for a storm or showers to scrub the spores out of the air," Shaner says. "Otherwise many of them remain airborne aloft. They eventually will settle out, but it's more dramatic if a rain event scrubs them out of the atmosphere."

Shaner and many more Extension personnel will be watching as the '07 growing season unfolds. He will once again maintain sentinel plots across Indiana to help in early detection of soybean rust. And he will be in contact with Extension personnel across the country who are also working with early-detection sentinel plots.

Watching the weather models will also be important, Shaner says. If infection develops in key areas, such as Louisiana, then models depicting likely air pattern movement and storm activity will become extremely important.