Georgia’s famous sweet Vidalia onion crop has a new virus. And
state agricultural experts want to control it before it can
damage the state’s official vegetable.

In September, mysterious straw-colored lesions appeared on the
leaves of onion plants in Georgia seedbeds, said David
Langston, a plant pathologist with the University of Georgia
College of Agricultural and Environmental Sciences.

Iris yellow spot virus

Since then, tests conducted on the Coastal Plain Experiment
Station in Tifton, Ga., have led scientists there to believe
the lesions are symptoms of the iris yellow spot virus.

Langston and other UGA scientists are working with the Georgia
Department of Agriculture and onion growers to assess this
possible problem.

The Vidalia onion crop, Langston said, is not under siege by
this or any other disease right now. Most of the crop is in
good shape. The weather has been kind so far, and pressure from
other diseases has been light.

“We’re not sure how this new virus will impact Georgia’s onion
industry,” Langston said. “But the potential threat from this
virus is alarming.”

Problem?

The virus, he said, can prevent an onion plant from making
enough food to properly develop a bulb, make it vulnerable to
other disease or kill it.

The virus cannot harm humans.

This virus has caused problems for onions and onion-related
crops like garlic and leeks in Oregon and Idaho and other parts
of the world. If it takes a foothold in Georgia, it has the
potential to become enemy No. 1 for the state’s onion crop,
worth about $75 million a year.

IYSV is transmitted by onion thrips. Thrips are tiny insects
that feed on plant leaves. Onion thrips have been in Georgia
for some time, but they’re not commonly found.

The virus doesn’t make thrips sick, but it can reproduce and
grow inside of them. That’s one reason this virus and others
like it concern scientists. It can be hard to pin down and
control.

“This is a very dynamic type of virus that can survive in both
thrips and plants. That’s unique,” Langston said.

Foreign invader?

It can’t be said exactly how the virus got into Georgia. But
it’s believed that it may have caught a ride inside thrips on
onions from Peru.

Peru has the virus. Some Georgia onion growers import Peruvian
onions to sell around September, when stored Vidalia onion
supplies dwindle.

IYSV is related and very similar to the notorious tomato
spotted wilt virus. Since TSWV blew in on thrips from Texas in
the late 1980s, it has caused millions of dollars of damage to
many Georgia vegetables and hundreds of millions of dollars of
damage to peanut and tobacco crops.

TSWV is also now being detected in some Vidalia onion fields,
Langston said. And if this new virus acts like TSWV, it’s
probably here to stay.

There is no cure for the virus.

Sample, monitor

But UGA scientists recommend that onion growers who imported
Peruvian onions this year use herbicides and insecticides to
destroy any cull piles left on their farms. When growers get
Peruvian onion shipments, they go through them and discard, or
cull, any damaged or deformed onions.

Scientists will continue to take samples and monitor the entire
onion-growing region this year for the virus. If the threat of
the virus grows, new management practices will have to be
developed to deal with it, he said.

“We are now in a prepared wait-and-see situation,” Langston
said.

There are 134 registered Vidalia onion growers in the 20-county
production area. Most are grown in Tattnall and Toombs counties
in east central Georgia. Growers usually plant around 13,500
acres of onions each year.