Published on 01/17/04

New virus could become Vidalia onions' No. 1 enemy

By Brad Haire
University of Georgia

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."


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.

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