Published on 07/28/97

UGA Scientists Seeking Answers to Crop Disease

University of Georgia scientists are trying to help Georgia farmers stop a virus-borne disease that has hit crops especially hard this year.

"It's the worst we've seen in Georgia," said Albert Culbreath, a plant pathologist with the UGA College of Agricultural and Environmental Sciences.

"We're seeing tomato spotted wilt virus levels up to 70 percent in some fields this year," he said. "It's not that severe in every field. But it's doing more damage over more fields over a greater area than in years past."

A virus causes this killer disease that can wipe out peanuts, tobacco, peppers and tomatoes. It's hit all four crops hard this year. And Culbreath expects the damage to continue.

"When the virus hits this hard, as early in the season as it did this year, the impact is greater than when it hits late, as it did in 1996," he said.

Georgia farmers lost close to $75 million to TSW last year. Culbreath and others expect the damage to be greater this year.

There's no cure for TSW once plants are infected. And even some more resistant varieties are infected, though not as bad as others. "It's a matter of living with it for this year," Culbreath said.

But farmers can help prevent it next year.

John Baldwin, a CAES extension agronomist, said farmers have to work wholeheartedly to reduce TSW. "They have to use every tool available to keep it out of their fields," he said.

He tells farmers to plant resistant cultivars, plant when TSW is least likely to infect and plant a good population to set a good stand.

Baldwin said setting a good stand helps in several ways. Thrips, the insects that carry the virus, don't seem to invade thickly planted fields as much as those with fewer plants. And if they do, more plants can mean more yield overall, even if the yield is reduced by disease damage.

At the UGA Coastal Plain Experiment Station in Tifton, CAES horticulture researcher Sharad Phatak has found another way to help fight the virus.

"We found that in conservation tillage, where you have the residue of rye or wheat or other cover crops on the surface, you can see a reduction on 30 percent in (TSW) virus," he said.

The TSW reduction is only one of Phatak's findings during six years of research in peanuts and another 12 years in tomatoes and peppers. But it's the most exciting to many farmers.

The reduction isn't a direct result of conservation tillage. It's an indirect way to prevent the disease. But it works.

The crop residue provides a place for beneficial insects to live, Phatak said. Those insects feast on insects, including thrips, that can cause damage and yield loss.

Phatak found conservation tillage leads to better quality in peanuts, too.

Coffee County farmer Max Carter likes using no-till in his peanuts. "We're seeing a lot of crop residue building up, making more organic matter in the soil," he said. "Soil erosion is zero, too, and the water stays clean and clear."