Published on 02/09/06

Crop disease risk high on winter bug count

By Brad Haire
University of Georgia

Thrips, tiny insects that can carry a deadly crop disease, have weathered south Georgia’s winter better than usual. Farmers should think about taking precautions this spring, says an expert with the University of Georgia College of Agricultural and Environmental Sciences.

Thrips can get the tomato spotted wilt virus from an infected plant when they are nymphs. When they get older, they can carry the disease to other plants as they feed, said David Riley, a CAES research entomologist in Tifton, Ga.

The severity of the disease can vary from year to year. Over the past two decades, TSWV has cost Georgia farmers hundreds of millions of dollars in damage to crops like peanuts, tobacco, peppers and tomatoes.

“Conditions in south Georgia are developing to an increased risk of tomato spotted wilt virus this spring,” he said.

Thrips count

Two years ago, Riley and his research assistants began to keep track of thrips in Brooks, Colquitt, Decatur and Tift counties in south Georgia, the region where most of the peanut, tobacco and vegetable crops are planted.

They collect weed samples monthly from two sites in each county. They collect every two weeks during the months leading to spring planting, he said.

Thrips numbers are running high, he said, twice those taken this time last year from Colquitt and Tift counties. Five percent of the weeds sampled in these counties are infected with TSWV. Based on research, anything above 2 percent now would indicate a risky year ahead.

The numbers in Brooks and Decatur counties are about the same as last year.

Thrips don’t like cold weather. They stop reproducing and become dormant when temperatures sink below 50 degrees. But it takes a few days of hard-freezing temperatures to kill them, he said.

Thrips have liked the recent warm weather in south Georgia, leading to the higher numbers, he said. Daytime temperatures in the region reached the mid- to upper-70s in late December and January – 10 degrees to 15 degrees above normal.

When temperatures get this high, thrips that survive winter become active. They’re hungry and ready to reproduce.

A female thrips can produce five to 90 more female thrips. Each can reach maturity in about two weeks and produce another 5 to 90 more. A field of peppers, for example, could have 10 million thrips per acre by April, Riley said. And that’s a conservative number.

Cool weather returned to south Georgia in the past week. This could suppress thrips’ activity. But what is believed to be their favorite food has emerged, too. Pine pollen now covers most fields, homes and cars in south Georgia, ready to give thrips a nutritious springtime kick once warm weather returns.

No cure

Prevention is the only cure for TSWV. Once a plant gets it, it will die or yield little. To protect their crops, farmers can spend more money for TSWV-resistant crop varieties and insecticidal sprays to control thrips.

Many farmers grow vegetables in fields of raised beds wrapped in plastic film. This helps farmers better control the crop environment. Most use black film. But some use metallic film, which disorients thrips and keeps them from landing on crops' leaves. It costs about $150 more per acre to use.

TSWV was bad last year. It cost Georgia tobacco farmers about $10 million in damage and control costs. It was tough on peanuts, too, reaching levels not seen since the late 1990s, when it cost farmers about $45 million in damage.

“Based on the thrips survey data,” Riley said, “the disease could be strong this year and become a problem earlier.”

To learn more about TSWV or the survey, go to the Web site at

A farmer who would like to have his area sampled should contact the local UGA Cooperative Extension office at 1-800-ASK-UGA1.

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