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.”