Published on 01/20/97

Ounce of Prevention Equals Pound of Peanuts

It's a virus, it's incurable and it has cost Georgia peanut farmers more than $50 million in just the past two years.

But farmers now have a new tool to assess their crop's risk for the deadly tomato spotted wilt virus. Now they can learn how to reduce that risk.

"There isn't anything farmers can do for their crop once it's infected," said Steve L. Brown, an entomologist with the University of Georgia Extension Service. "We have to avoid high-risk situations."

Tomato spotted wilt is a viral disease that can wipe out a peanut crop.

Albert Culbreath, a plant pathologist with the UGA Coastal Plain Experiment Station, said the virus attacks the plant, interfering with peanut production. Instead of growing leaves and peanuts, the plant begins making more viral cells.

It also makes the plant more susceptible to other diseases and more sensitive to environmental stress, including drought, excess moisture and insects.

In the past they've tried to control its spread by controlling the thrips that carry it from field to field. Those efforts have proven nearly worthless. By the time farmers spray to control the tiny insects, the plants are already infected.

But they can change some practices that affect the disease's severity.

Research in the UGA College of Agricultural and Environmental Sciences shows that many factors affect whether and how severely TSW will infect a field.

Brown said no single factor effectively controls the disease. But together they can change how TSW affects peanut yields.

"Peanut variety, planting date, plant population, virus history in the field and at-planting insect control all affect how likely the virus is to cause problems," he said.

In 1996, the scientists created a simple-to-use index of those risk factors. Farmers now can use the index to lower their risk of getting TSW in their peanut fields.

Tomato spotted wilt virus struck fast and hard in nearly all of Georgia's 533,000 peanut acres in 1996. "We saw a higher incidence of it in 1996 than in 1995," Brown said. "But yield losses were greater in 1995."

The disease struck later in the season in 1996. The later it infests a field, the lower its impact on yields.

The disease has infected Georgia peanuts only in the past 10 years. But it has become more important every year since it was found in 1986.

TSW cost peanut farmers as much as $33 million in 1995 -- about 8 percent of the crop's total value.

"Losses due to tomato spotted wilt were estimated to be greater than any other disease in 1995," Brown said. "You can't cure it, but farmers can change their management practices to reduce the damage TSW can do."

Worth County peanut farmer Johnny Cochran said TSW "nearly wiped out my 1995 irrigated peanut crop -- I had to do something!" Cochran figures he lost about 1,000 pounds per acre.

Cochran used the risk index in 1996 and decided to change his peanut variety, his planting dates and how he treated for insect control.

"We've got to approach this problem from several different directions to conquer it," he said.

Georgia peanut farmers send about half their crop, nearly 700 million pounds, to peanut butter factories.

In fact, about half the peanut butter produced in the U.S. is made from Georgia peanuts. The average American eats about 3.3 pounds of peanut butter every year.

Brown said the risk index is a unique way to manage a pest. "This is the first risk index that I know of," he said.

Since there is no cure for TSW, prevention is everything -- and the only thing -- that can make a difference.

"This isn't the perfect answer to tomato spotted wilt," Brown said. "But it's a good first step at dealing with the problem."