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Watching for Asian soybean rust

Test plots at Baton Rouge, La., last year showed that Asian soybean rust can defoliate plants within seven to 10 days after the disease is detected. But all is not lost once it is found, according to an LSU AgCenter expert.

“This was a graphic illustration of what we heard takes place in Brazil,” said LSU AgCenter plant pathologist Ray Schneider. Schneider’s presentation came during a meeting called by BASF to promote its fungicide, Headline. Schneider said an LSU AgCenter test last year appeared to show that Headline treatments were effective against rust.

“Rust is easily manageable if you get the material out there at the right time,” Schneider said.

Many chemicals are considered curatives of Asian soybean rust, but that is a misnomer, according to Schneider, who stressed, “All you can do is arrest it from moving from affected leaves to unaffected, and then you have to do it early.”

Schneider said Brazilian growers are comfortable that Asian soybean rust does not affect yields if it occurs after the R-6 stage of growth, but that rule of thumb doesn’t seem to apply in Louisiana.

Finding Asian soybean rust at low levels before it is evident is difficult, Schneider said. But if it has shown up in other areas such as east Texas or southeast Louisiana, “and you still haven’t found rust, it’s time to spray.”

Asian soybean rust has been found in several locations in the United States over the past few years, including Texas, Florida and Iowa.

Boyd Padgett, another LSU AgCenter pathologist, said last year’s testing of several fungicides on soybeans showed promise against cercospera, frogeye, aerial blight and Asian soybean rust.

Headline worked well on stripe rust and leaf rust, he said, and some of the best results came with Propimax followed by Headline.

Spraying has to be done correctly to maximize effectiveness at preventing disease, Padgett said. A good rate for aerial application is 4 to 5 gallons per acre, and ground application should be used at a rate of 10 to 20 gallons per acre. Nozzles should be cone, flat fan or twin flat fan, he said.

David Lanclos, LSU AgCenter grain specialist, said using fungicides on corn showed promise in multiple tests last year, but the AgCenter does not have enough data to make a recommendation. “We feel the data is strong enough that there is something going on,” Lanclos said.

Lanclos said the U.S. Department of Agriculture’s recent crop forecast calls for Louisiana corn planting on 700,000 acres — about double the 2006 total.

Lanclos said his figures are closer to 625,000, “but that could go up.”


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