Originally created 01/13/04

Mystery disease not so sweet for Georgia's Vidalia onion crop



ALBANY, Ga. -- Researchers are scrambling to identify a mystery disease that has emerged for the first time as a threat to Georgia's $75 million crop of Vidalia sweet onions.

Tests are being conducted on lesions that have started appearing on the leaves of onion plants in seed beds. Scientists are trying to find out whether they have a unique cause or are related to tomato spotted wilt virus, which has plagued Georgia peanuts and tobacco, or iris yellow spot virus, which has damaged onion crops in South America and the northwestern United States.

"This is the first year it's come to our attention," said Reid Torrance, a University of Georgia extension coordinator in Tattnall County, the state's largest Vidalia-producing county. "It's also the first year we've tested for it."

Onion seeds are planted in beds starting in September. When the plants are large enough, usually in November and December, they are replanted in fields.

Georgia's 134 registered Vidalia growers harvested 12,500 acres of onions last year. There are no official estimates yet for this year's crop, but experts believe it could be larger than in 2003.

The disease causes spots on the plant leaves and does not appear to be any of the typical bacterial or fungal diseases that attack onions, Torrance said Monday.

Glennville grower Delbert Bland, who had to replant 200 acres because of the problem, believes a virus is to blame.

He emphasized, however, that once the causes is known, possibly in a week or two, growers can take measures to curb it.

"It's one of those things that, if you ignore it, you can have a crisis," he said. "If you go out there and treat it and do a good job, you can overcome it."

Tomato spotted wilt and iris yellow spot are spread by tiny insects known as thrips that feed on plant juices. The most common thrips in Georgia are tobacco thrips and western flower thrips. Now there's a third - onion thrips - that have come in on imported onions from Peru, Torrance said.

Vidalia onions are available in May and June, fresh from the fields. Some onions are stashed in atmosphere-controlled warehouses to extend the season through October. During the offseason, some growers import sweet onions from Peru and other Latin American countries so they can market onions year-round.

Torrance said onion thrips on Peruvian onions have tested positive for both tomato spotted wilt and iris yellow spot virus, but no one is sure that either of those has caused the upsurge of leaf damage.

"Our university research team has injected some onion plants with each of the two viruses to see what type of symptom is generated," Torrance said. "We need to try to create the same symptom we're seeing in the field before we say conclusively ... what caused it."

Farmer Moses Coleman started Georgia's onion industry near Vidalia, about 80 miles west of Savannah, in 1931 when he noticed that his first crop was unusually mild. Other growers joined in and began promoting the sweet onions with a campaign that said you could "eat 'em like an apple."

A Vidalia has to be a yellow granex variety that is flatter than tall and meets the industry's standard for sweetness and mildness - a standard that is written into state law. The Vidalia name is a trademark of the Georgia Department of Agriculture.

Bland said his crop looks good so far, but a lot can happen between now and harvest.

His advice for growers is, "Make sure you're in church every Sunday."