By Brad Haire
University of Georgia

Tomato spotted wilt virus hurts many crops in Georgia. But its
severity varies from year to year. University of Georgia
scientists are developing an alert to help vegetable farmers
know how bad it will be each year before they plant.

“If a grower knew how bad TSWV might be before transplanting in
the spring, he could make some management decisions that could
save money or better protect the crop,” said David Riley, an
entomologist with the UGA College of Agricultural and
Environmental Sciences.

Since appearing in Georgia in the late-1980s, TSWV has cost
Georgia farmers hundreds of millions of dollars in damage to
crops like peanuts, tobacco, peppers and tomatoes.

The carrier

TSWV is carried by tiny insects called thrips. They get the
virus when they feed on infected plants. When they leave those
plants, they can carry the virus to healthy ones. Millions of
thrips per acre can visit a field in a year.

Prevention is the only “cure” for the virus. Once a plant gets
it, it will grow poorly or die.

Thrips’ populations drastically decline in winter. But a few,
Riley said, retreat to the weeds that surround fields. They
survive there until spring and then return, possibly with the
virus, to freshly planted vegetables.

In the weeds

Starting last summer, Riley and other CAES scientists began an
extensive survey of weeds and thrips numbers in Brooks,
Colquitt, Decatur and Tift counties. A large portion of
Georgia’s vegetable crop is grown in these counties. Each month,
weed samples are taken from two field sites in each county.

They want to know if weeds near the fields have TSWV and if
thrips are feeding and reproducing on these weeds. They will
focus on the data taken in February and March.

High numbers of samples with TSWV and thrips at this time will
indicate a high risk for the spread of the virus. If this
happens, an alert will be issued.

With this information, farmers can decide how best to protect
their crops in the spring. “This can be another tool and service
we can provide that farmers can use to know what to expect,” he
said.

Farmers can help. They can fill gallon-size plastic bags with
weeds, particularly chickweed, cudweed, sow thistle, swine cress
and Carolina geranium, from around fields planted with peppers
or tomatoes. They can submit samples to their county UGA
Extension Service agent or contact Stan Diffie at (229) 386-
3374.

Warm winter weather tends to increase thrips populations, Riley
said. He’s noticed a correlation, too, between the tree pollen
amounts and thrips populations.

Thrips like to eat, among other things, pine tree pollen. “The
increase and decrease of pollen seem to mirror the increase and
decrease of thrips populations each year,” Riley said.

Protection

To protect crops, vegetable farmers spend extra money on TSWV-
resistant crop varieties and insecticidal sprays to control
thrips, he said.

Many Georgia vegetables are grown in fields of raised beds
wrapped in plastic film, mostly black. This helps farmers better
control the crop environment.

Some farmers have started using more expensive reflective
metallic film. Many believe it disorients thrips and keeps them
from landing on crops’ leaves.

Forecast tools exist for other crops. One developed by North
Carolina State University predicts each year the possible
severity of blue mold, a fungus that attacks tobacco. And
research by CAES scientists has shown that Doppler radar can
help peanut farmers know when to effectively apply fungicides.