UGA
CAES

Georgia onion growers don’t usually think of insects as a
major problem. But thrips can
take a bite out of the sweet onion crop, said a University of
Georgia scientist.

Even a few causeÿ some
damage

“Even a relatively small population can have a
significant yield impact,”
said UGA entomologist David Riley.
“Thrips damage the leaves. Without healthy leaves, the
bulbs can’t develop to their
potential.”

Riley said he’s seen thrips populations increase during
the past three years of his
research at the Tifton campus of the UGA College of
Agricultural and Environmental Sciences.

“Thrips aren’t going to wipe out the Georgia onion
crop,” he said. “But
they definitely can reduce yields.”

Treatment needed and
effective

Riley said this year one-third of Georgia’s 17,000
acres of onions may need thrips
treatments they’re not getting.

“With effective control of the higher thrips numbers
this year,” he said,
“farmers could add about $4 million every year to the
value of the crop.”

In 1998, Riley’s research revealed that fields with
effective thrips control produced
more and larger Vidalia-type onions. For about $100 per
acre in treatment cost, farmers
can pocket another $900 in onion value from fields where
thrips are at damaging levels.
Without treatment, the farmers harvested fewer jumbo and
large onion bulbs.

J. Cannon, UGA CAES

IMMATURE ONIONS like these are most prone to thrips damage during March, April and May. The thrips damage the leaves, weakening the plant and preventing full bulb growth.

The damage they
cause

David Adams, a UGA
Extension
Service entomologist, said the thrips weaken the
plants. “They use their rasping
mouthparts to damage the plant cells and lap up the
juices,” he said.

When it hurts the farmer, it hurts the consumer, too,
Riley said. “If the supply
is lower,” he said, “consumers will have to pay more for
these onions.”

Research efforts paying
off

But with Riley’s research data, farmers can be sure
their thrips control dollars will
pay off in the long run. He’s working to learn what thrips
species damage onions and when
it’s most effective to apply insecticides.

Adams said that the insects cause varying levels of
damage at different times in the
season.

“If a lot of thrips are in the field early in the
season, they can damage young
plants as the bulbs are forming,” he said. “Effective
control is vital
then.”

Later in the season, he said, a few thrips may not
cause as much damage. “However,
in Georgia, thrips populations are highest during March,
April and May,” he said.
“So control efforts should be aimed at thrips during the
spring.”

Spotting the
problem

The damage thrips cause is hard to see. The insects are
no bigger than the period at
the end of this sentence. It’s hard to spot them.

Bo Herndon, an onion farmer in south central Georgia,
said he has to look hard to see
thrips in his fields.

“I’ve really got to get down and look close,” he
said. “And even then,
you’ll probably see the damage first. They’re easier to
see if there are a lot of them.
And at that point, it’s time to treat — fast!”