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Source: Cheminova news release

With back-to-back mild winters, chances are a yield-robbing disease will strike southern soybean fields this year. Warm and humid is how soybeans like their weather, and the same holds true for soybean disease, warns Heather Young-Kelly, Extension plant pathologist for the University of Tennessee.

"If we start to see disease pressure early on in the season and the forecast is favorable for rain and humid weather, it is going to be a good year for yield as well as disease. It is good to scout to catch the first signs of disease and then apply a fungicide. Most fungicides work best as a preventative," she notes.

Young-Kelly identified strobilurin-resistant frogeye leaf spot in two research plots in different locations in 2012. Where fields are suspected to have a mix of strobilurin-resistant and nonresistant frogeye leaf spot, it is important to use a program that tackles both strains, she says.

She advises a single application of a product combining a strobilurin and triazole fungicide, or two applications of alternating chemistries.

"Frogeye leaf spot is very common with the usual rainfall pattern. And now that we have had two mild winters in a row, and unless the South gets a cold snap, rust could be an issue," she adds.

In most years, Louisiana growers will encounter Cercospora leaf blight much more than soybean rust. But last year was unusual, notes Raymond Schneider, research plant pathologist for the Louisiana State University Agricultural Center.

"It can be difficult to predict which disease may strike," he observes. Cercospora leaf blight can cause significant yield loss if untreated. An early stage R1 application of TOPGUARDŽ, which is made by Cheminova, can boost yields by at least 15% under heavy disease pressure and cut disease severity from 84% to less than five percent, says Schneider.

In a typical year, that's why growers will use TOPGUARD. In 2012, TOPGUARD provided the double benefit, by protecting fields against soybean rust as well. "We were hammered with soybean rust," says Schneider. "The amount of rust was spectacular."

He cautions that rust may be a problem again this year. Already it has been identified as overwintering in kudzu and volunteer soybeans in southern Louisiana.

Schneider emphasizes the importance of chemistry selection and encourages growers to stay current on university research specific to their state. He notes that in 2012, TOPGUARD controlled soybean rust, while several strobilurins that worked well in the past, did not perform as well as expected.

Growers in Alabama are also advised to be alert to heightened disease pressure. In 2012, all 67 counties in Alabama reported rust. This year, it has already been identified on kudzu in downtown Montgomery.

"We have some idea of where rust might be overwintering, but we really wait until the last hard frost to predict how prevalent it may be," says plant pathologist Ed Sikora at Auburn University. "If we have a mild winter, you start seeing situations like Louisiana. That's when growers in those areas need to be aware that they have soybean rust inoculum in their backyard even before they plant.

"Last year was a good year to study soybean rust. The fungus overwintered along the Gulf Coast. Then in May we started to observe it spread northward. So we were putting out alerts in May-"soybean rust is here, be prepared," says Sikora.

"We try to alert growers to the presence of soybean rust so that they can better manage their fungicide spray program," he adds.

Mississippi, southern Missouri and Arkansas soybean growers may want to review their soybean disease management programs as well. The USDA IPM Soybean Rust Network ( reports that in 2012 soybean rust was identified in 82 counties in Mississippi and 21 counties in Arkansas. All three of these states have reported confirmed cases of strobilurin-resistant frogeye leaf spot in soybeans, in recent years.

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