Window For Soybean Rust Infections Slowly Closing

Linda Benedict  |  7/15/2006 1:45:32 AM

News Release Distributed 07/13/06

Louisiana soybean producers are sitting on pins and needles waiting to see if their soybean crops will pass a critical growth stage without being infected by Asian soybean rust.

"Our best estimate is that 50 percent to 60 percent of the state’s soybeans will be past the susceptible period in 7 to 10 days," said Dr. David Lanclos, the LSU AgCenter’s state soybean specialist.

The rust disease, which is spread by windborne spores, is feared because it’s hard to detect until it’s too late to do anything to control it. The symptoms first appear on the bottom leaves – hidden from view. By the time it’s obvious, the disease, which has been known to destroy entire fields, generally has taken hold.

Lanclos said the problem with the rust disease is that it causes soybean plants to defoliate prematurely and reduces the photosynthesis process. Once the critical period is past, however, the bean yields will not be negatively affected if the plant loses its leaves.

"When the plants start to dry down – or senesce – we’ll be out of the woods," Lanclos said. "But southwest Louisiana and portions of central Louisiana are still vulnerable."

Asian soybean rust has been confirmed in three kudzu patches in Louisiana this year, said Dr. Clayton Hollier, LSU AgCenter plant pathologist. The third confirmation occurred on July 12 in Iberia Parish, the second sample found in that parish. The first was in Lafayette Parish on June 30.

"No one has found the disease in soybeans in Louisiana this year," Hollier said.

Lanclos said producers and AgCenter observers are still diligently looking for the disease. If it’s found in soybeans, the word will immediately go out to producers to apply fungicides to their soybean fields that have not passed the critical growth stage.

Lanclos said growers had been advised to apply a fungicide to their soybean fields during early stages of growth for protection as they customarily do each year. If Asian soybean rust is identified in a soybean field and the crop hasn’t passed the critical growth point, they’ll be encouraged to apply another fungicide as treatment.

Some farmers apply fungicide to their soybean fields to control other diseases including cercospora and aerial blight, Hollier said.

"It wouldn’t cost too much more to add fungicide for rust," Hollier said.

AgCenter experts are not at this time recommending that soybean farmers apply fungicides wholesale on the soybean fields. Even if the disease is found in soybeans, the recommendation is to apply fungicide only to the fields where the beans are forming, Hollier said.

"The soybeans need protection during the critical reproductive stages of R-3 to R-5," Hollier said.

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Contacts:
David Lanclos at (318) 473-6530 or dlanclos@agcenter.lsu.edu
Clayton Hollier at (225) 578-2186 or chollier@agcenter.lsu.edu
Writer:
Rick Bogren at (225) 578-5839 or rbogren@agcenter.lsu.edu

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