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Old disease coming back to haunt 'new' watermelons

By Brad Haire
University of Georgia

Georgia farmers mostly grow seedless watermelons now because folks don't like to spit seeds anymore. But this has allowed an old, deadly plant disease to make a comeback, says a University of Georgia specialist.

"I think watermelon growers are unfortunately planting themselves into a corner," says David Langston, a plant pathologist with the UGA College of Agricultural and Environmental Sciences.

The problem is a fungal disease commonly called fusarium wilt that can live in the soil for years, he said. It's now popping up more frequently in Georgia watermelon fields, attacking the vascular systems of infected melon vines, choking off water and nutrients and eventually killing the plants.

Some growers have had to destroy entire fields due to the disease, he said. "Once a melon gets fusarium wilt it can't be cured."

The first documented case of fusarium wilt in watermelons was in Georgia around the turn of the 20th century. Over the years, the industry developed varieties with resistance to the disease, he said. But all of these varieties have seeds. The disease could still cause isolated problems and was a threat, but it was controllable.

But watermelon eaters now demand melons without seeds. Seedless watermelon varieties have been around for many years, but over the past five years they've become the most widely grown melon type in Georgia and in other watermelon-growing states like Florida and Texas.

But along with the increase of seedless watermelon growing has come an increase in fusarium wilt, he said.

"We've seen a considerable increase in calls and plant samples that have been diagnosed as fusarium wilt," Langston said. "They come in every day, several times a day. It is always the same story, only seedless are affected."

Every watermelon-growing county in Georgia has had reports of the disease in seedless melons, he said. Most Georgia melons are grown in the south-central part of the state.

"Growers should be very concerned if they want to grow seedless melons in the future," he said. "We haven't seen any widespread significant yield losses yet. But we will, as long as we continue to grow seedless melons with no resistance."

A few seedless watermelon varieties have resistance to the disease. But they aren't popular to grow, he said.

Growers could lower their risk for the disease by planting a field in watermelons only every eight years. But growers, due to limited land, usually plant watermelons back to back each year in the same fields. Or they skip only one year.

This compounds the problem, Langston said, because fusarium wilt can live and build up in fields that are planted in watermelons each year.

There is an alternative. In Japan and in some European countries where land is limited, watermelons are grafted onto squash, pumpkin and gourd vines which are resistant to fusarium wilt. But the process is labor-intensive and costly for farmers. It costs consumers, too. One watermelon in Japan can cost as much as $25.

Georgia growers will soon start harvesting the first of this year's crop. Most Georgia melons are grown to target that quintessential watermelon-eating holiday: the Fourth of July.

Despite the looming threat of this disease, Georgia's watermelon crop is expected to be a good one this year. A dry spring could hurt overall yields, Langston said, but it has kept other diseases like gummy stem blight and downy mildew to a minimum.

Georgia is a close second to Florida in overall watermelon production, growing about 25,000 to 26,000 acres annually.

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

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