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Spotted wilt virus slams Georgia peanut crop

By Brad Haire
University of Georgia

Every peanut farmer in Georgia has heard of it. And this year, it's been pretty bad.

"Tomato spotted wilt virus has been very severe across the state in peanuts," said Bob Kemerait, a plant pathologist with the University of Georgia Extension Service.

Not Surprised

The severity of the disease was not unexpected, he said, because it was bad on tobacco and backyard tomatoes this year, too.

Some fields are 100 percent infected, he said, even in peanut varieties that are resistant to the virus. But not all fields have been so severely affected.

"I don't know that this is the most severe we've ever seen," Kemerait said. "But it's certainly the most severe on peanuts in the past few years."

The virus didn't treat peanuts too badly last year. "I believe many growers began to think we turned the corner on the disease, so to speak," he said. "Unfortunately, that was not the case."

Management

Some growers this year became a little lax in managing the disease and didn't, or were unable to, follow UGA's TSWV Risk Index as closely as they might. The index provides guidelines to reduce risk for the virus.

And TSWV-resistant peanut varieties, like Georgia Green and C99- R, aren't totally immune to the virus, especially in years with a lot of it around.

"Fortunately, newer, more resistant varieties appear to be on the horizon," Kemerait said.

Those Thrips

TSWV is spread by small insects known as thrips. Thrips pass the virus to peanut plants when they feed on them. The virus reproduces and spreads throughout entire plants. In many cases, it dwarfs the plants. Yields can be low or nonexistent if the virus attacks plants early in their growth.

UGA scientists have proven that the date on which peanuts are planted has a lot to do with the risk of getting the virus.

In the past, planting after May 1 was better. However, this year it appears, at least from preliminary observations, that the key was to plant after May 10.

"Peanuts planted before that often, but not always, had more severe TSWV," he said.

Research Continues

Plant pathology research has found an association between the severity of the virus in peanuts and the severity of TSWV in tobacco and rainfall in the spring. Tobacco is planted before peanuts.

"Perhaps, the rainfall in the spring affects some aspect of the insects' life cycle," Kemerait said.

To stay ahead of this disease, UGA breeders, researchers and other specialists keep looking for varieties with improved resistance. They continue to update the TSWV Risk Index to give the growers information on steps they can take to reduce the impact of the disease.

"We're still growing peanuts and will continue to do so," Kemerait said.

Due to recent tropical storms, the harvest of the Georgia peanut crop is slightly behind the five-year average. As of Sept. 22, only 29 percent of the peanuts had been dug, and only 18 percent had been harvested, according to the Georgia Agricultural Statistics Service.

(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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