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 www.caes.uga.edu/topics/diseases/tswv/.
A farmer who would like to have his area sampled should contact
the local UGA Cooperative Extension office at 1-800-ASK-UGA1.
