Published on 08/19/04

Warm, wet Georgia summer helps crops, diseases

By Brad Haire
University of Georgia

Georgia's usually wet, warm summers are good for row crops like peanuts, cotton, corn and soybeans. But they're also good for diseases that can attack plants below and above ground. And the recent surge of tropical weather can help the diseases.

"Over this growing season, except for a few stretches of dry weather, we've had pretty uniformly wet, warm weather across the state," said Bob Kemerait, a plant pathologist with the University of Georgia Extension Service. "This has been optimal for many plant diseases."

Tropical trouble

The wet weather brought by recent tropical storms did end a dry spell, he said. But it also increased the risk for many fungal diseases.

"Wind-blown rain can spread spores," he said. "And rain can splash spores onto plants."

Storms coming up from the Caribbean can carry spores a long way, too -- as far as the Southeastern United States, he said.

One spore can cause what is known as peanut rust. It sometimes affects peanuts in the Florida Panhandle but can reach Georgia, too.

"This is an explosive disease and can tear down a plant pretty fast," Kemerait said. "If rust appears, (farmers) better get out there and jump right on it."

Spraying can control this disease. But many farmers simply can't get tractors into fields when rain saturates the ground. They bog down.

"The rain is needed. But farmers need to be able to get into fields to apply fungicides," he said. "If they can't, it could really hurt yields."

In the fields

Peanuts have already had trouble with other more common diseases this year. Leaf spot and white mold have been widespread over the state. And tomato spotted wilt virus, a disease spread by small insects called thrips, has been bad. Some fields have been as much as 30 percent infected with the deadly disease. Last year, the virus was not as bad.

Georgia growers planted about 575,000 acres of peanuts this year, about 35,000 more acres than last year, according to the Georgia Agricultural Statistics Service.

Georgia's soybean growers have had problems with frog-eye leaf spot and downy mildew.

"I've had more calls this year for soybean disease than all the other crops combined," Kemerait said.

Fungicide spraying can control frog-eye. Downy mildew has no real control measures.

Soybean growers planted about 250,000 acres of soybeans this year, about 60,000 acres more than last year, according to the GASS.

Cotton growers have seen an increase this year in southern root knot nematodes in some fields. These microscopic worms damage root systems.

A problem that continues to perplex cotton farmers and researchers is "hard lock." This is when a cotton boll opens but the lint doesn't fluff, making it impossible to pick. It could be caused by a fungus.

"But we're not sure what causes it," Kemerait said. "But there's starting to be a lot of talk about hard lock."

Georgia has 1.3 million acres of cotton this year, a small increase from last year, according to the GASS.

Southern corn leaf blight has been a problem for Georgia corn growers this year, he said. It's usually a minor disease. Southern rust usually causes problems, but not this year. Both diseases attack corn leaves, especially during wet weather. And on varieties with reduced resistance, they can reduce yields.

Farmers have picked about half of Georgia's corn crop so far. They planted about 330,000 acres, about 10,000 less than last year.

Each year, plant diseases cost Georgia row-crop farmers about $150 million in lost production and the cost of preventive measures. "Overall, our crops are looking good," Kemerait said. "But this is a critical time of year for diseases."

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