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Researchers zeroing in on soybean rust

LSU AgCenter scientists are launching a series of research projects in 2005 to learn what they can about Asian soybean rust and how the potentially devastating disease will develop in Louisiana.

Meanwhile, they are telling farmers to go about their soybean planting as they have in the past, despite this looming threat.

“We don't know when we'll see Asian soybean rust again,” said Boyd Padgett, LSU AgCenter plant pathologist. “We don't know how it will react in Louisiana. There's a lot we don't know about this disease.”

In early November 2004, LSU AgCenter scientist Ray Schneider unexpectedly found Asian soybean rust in a production field on the Ben Hur Research Farm near the LSU campus. This was the first discovery of the disease in North America.

Asian soybean rust has been around since the early part of the 20th century. But it had been confined to Asia until recently — when it spread to Africa and then on to South America. It was first discovered in the Western Hemisphere in Brazil in 2000.

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 about it. The symptoms first appear on the bottom leaves — hidden from view. By the time a farmer sees it, the disease, which has been known to destroy entire fields, generally has taken hold.

Schneider's discovery prompted an emergency gathering of scientists from all over the country at the LSU AgCenter. They determined hurricane winds from August 2004 had carried the rust spores into the state — and, as it turns out, eight other states in the South.

No signs of the disease were found in the Midwest, the major soybean-producing area in the United States. But by the time the searches were being conducted in late 2004, all the beans up north had been harvested, and the weather had turned cold, which kills the disease.

To help with understanding the disease, a group from the LSU AgCenter will head to Brazil in mid-February to find out how farmers there have learned to cope. Soybean harvest starts there in February and March. Despite the presence of the disease, Brazil continues to be the No. 1 producer of soybeans worldwide.

Besides Padgett and Schneider, the LSU AgCenter delegation includes David Lanclos, Extension soybean specialist; Allen Hogan and Keith Normand, county agents; and Matt Baur, entomologist.

“2005 will be a learning year,” Lanclos said. “Until we find out something different, we will continue with the same recommendations for growing soybeans in Louisiana.”

The researchers will plant various types of soybeans at various times to see which ones might get rust. If the rust shows up, they'll spray different products at different times to see what works best.

Meanwhile, they're telling farmers not to spray with fungicide as a preventive measure, unless rust is confirmed in the state again this growing season. If rust is found, then they recommend using a fungicide.

LSU AgCenter experts also are strongly suggesting Louisiana farmers start scouting for signs of Asian soybean rust as soon as soybean plants emerge from the ground.

Asian soybean rust likes long periods of leaf wetness and warm conditions (60 degrees F to 80 degrees F), Padgett said.

“Look at the areas in your fields shaded from the morning sun,” Padgett advised a group of soybean farmers gathered at the LSU AgCenter's Dean Lee Research Station in January. “Know your other diseases. Start looking as soon as the plant's up.

“We don't know if this will be a minor disease or No. 1,” Padgett said. “We may be like Brazil with some years bad and some good.”

The main advice Padgett and Lanclos are giving Louisiana farmers is to not change a successful production system.

“Continue doing what has worked in the past,” Lanclos said. “Plant the varieties recommended by the LSU AgCenter.”

Lanclos predicts there will be fewer acres of soybeans grown in 2005 because of the uncertainties. In 2004, about a million Louisiana acres, the most for any crop, were in soybeans. Farmers in the southwestern area of the state may turn more of those acres into crawfish production. And those in northeast Louisiana may grow more grain sorghum, the experts said.

Soybeans are grown in Louisiana in 40 to 50 parishes, with the most grown in the northeastern part of the state — although the good soil there is saved for cotton.

Development of a rust-resistant variety of soybean is predicted to be at least five years away.

Linda Benedict writes for the Louisiana Cooperative Extension Service.

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