Asian Soybean Rust Found In Additional La. Fields

Clayton Hollier, Merrill, Thomas A., Lanclos, David Y.  |  7/21/2007 2:53:56 AM

News Release Distributed 07/20/07

Experts confirmed Louisiana’s first infestations of Asian soybean rust in commercial production fields in Central Louisiana this week.

"This is the first time we’ve seen a significant infestation in a commercial field with the surrounding areas also infested," said Dr. David Boethel, vice chancellor for research in the LSU AgCenter. "The good news, however, is that our scientists have been on top of the situation – watching sentinel fields, communicating with farmers and consultants, conducting research and much more to combat this problem.

"I think that the soybean producers in the state have been warned and have been poised to take action," he said, adding, "Many of them probably already have done so."

Among the potential actions are the use of fungicides to try to stem the effects of the disease, which has proven to be devastating to soybean crops in areas of South America.

This week’s discoveries came in soybean fields on farms in Avoyelles and Rapides parishes. Those infestations with Asian soybean rust were discovered July 18-19 after rust was discovered in a field near Cheneyville and experts fanned out looking for further clues about the disease.

Experts earlier had found the disease on "sentinel plots" – specially planted soybean fields that were being watched for any signs of the disease – in Avoyelles and Rapides in late June.

"There seems to be a marked increase in the commercial fields that are positive now," LSU AgCenter plant pathologist Dr. Clayton Hollier said. "It would seem to say that the fungus has built up enough that it is starting to spread and move more easily."

Asian soybean rust was first discovered in the United States in 2004. Although it’s been known to exist since the early part of the 20th century, it was largely confined to Asia until recently – when it spread to Africa and then on to South America around 2000.

Since its initial discovery in South Louisiana in 2004, where its windborne spores are thought to have come in on storm winds that summer, it has been seen in kudzu, another host plant, and on soybeans in a variety of southern states, including Florida, Georgia, Alabama, Mississippi and Texas.

Hollier said some of those states also are beginning to see increased activity of the disease.

"Environmental conditions this year have been conducive to promoting this and other soybean diseases," Hollier said, explaining that high humidity or rain and warm but not extremely hot weather are some of the factors.

"There also are areas of Texas where there had never been rust before that are now showing up with rust as a result of the storms they’ve had go through there this summer," Hollier said, explaining that experts across the region stay in touch with one another and share results about monitoring the disease. "There’s also a buildup going on in kudzu Mississippi now."

Hollier and LSU AgCenter soybean specialist Dr. David Lanclos pointed out the discoveries are significant because most of the fields where rust was discovered – and much of the state’s soybean crops – are at growth stages critical to yield potential.

Known as R4, R5 and R6, these latter parts of the plants’ reproductive cycles are where the soybean pods are formed and begin to fill.

"What the findings in these fields and the sentinel plots really give us and the farmers is a warning to be looking at commercial fields very carefully," Lanclos said. "The whole point is to really get out and scout for signs of disease."

The LSU AgCenter experts said growers need to look carefully at plants and to be sure to examine areas well within the canopies of the plants for signs of disease – rather than taking a look at just the tops. They also say to look carefully around tree lines where shade may keep plants cooler and allow moisture to stay on them a little longer.

In addition to rust, soybean producers also can face other plant diseases such as aerial blight, Cercospora diseases, pod and stem blight and anthracnose this time of year.

"That means they face decisions about what to do," Hollier said, explaining there are two broad groups of fungicides that can be used – triazoles and strobilurins.

"It all depends on what you find – or the timing of it," he said. "Strobilurins can be used to prevent rust, while triazoles can be used preventatively or after rust has occurred – to combat rust or prevent further development.

"When dealing with other diseases, however, the strobilurins do a better job against those pathogens than the triazoles do," Hollier continued. "So if you’re looking at a spectrum of potential problems, you want to use a mix of those two categories."

The experts said agents in parish offices of the LSU AgCenter can help soybean producers with identifying diseases and with recommendations about specific materials to use in combating those diseases.

“Our parish agents, state specialists and research scientists have been working very hard monitoring soybean fields throughout the state,” said Dr. Paul Coreil, vice chancellor and director of Extension for the LSU AgCenter. “This excellent teamwork has resulted in the best possible notice to growers on rust identification in fields and management options. We hope that will limit the economic impact of this new crop disease.”

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Contacts:
Clayton Hollier at (225) 578-4487 or chollier@agcenter.lsu.edu
David Lanclos at (318) 473-6530 or dlanclos@agcenter.lsu.edu 
Writer:
Tom Merrill at (225) 578-2263 or tmerrill@agcenter.lsu.edu

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