By Brad Haire
University of Georgia

Second only to actually buying the seed for a crop, fighting
diseases is the most essential thing a farmer has to do to grow a
successful crop in Georgia, said Bob Kemerait, a plant
pathologist with the University of Georgia Extension Service.

Georgia peanut farmers, for example, spent $65 million
fighting
diseases last year and still lost $50 million of their crop to
disease damage.

TSWV Terrorizes Farmers

Tomato spotted wilt virus began attacking several Georgia
crops,
including vegetables, tobacco and peanuts, in the mid-1980s. This
disease preferred an aerial assault. Carried inside tiny insects
called thrips, it has swept over much of the state. It continues
to terrorize farmers, especially peanut farmers.

This year, Kemerait said, TSWV has damaged as much as 70
percent
of some peanut fields. “Some growers had forgotten how bad it
could be,” he said.

Some diseases, like an infantry invasion, prefer to attack
head
on. Soreshin, a cotton disease, cuts plants off at the “knees,”
he said.

“The fungus nibbles at the plant at the soil line,” Kemerait
said. “It weakens the plant. The plant tends to topple over, like
the knees have been cut from beneath it.”

Cotton Bolls Provide Home

Sometimes plants open themselves up to an invasion by
providing
fertile campgrounds. This can happen when cotton bolls, the part
of the plant that produces the lint, first open. Rain can bring
into the open boll bacteria and fungi that find a wonderful
environment to flourish and destroy the boll, he said.

Boll rot caused $18.5 million in economic damage to Georgia
cotton in 2001 alone.

Some attacks take place underground. Plant pathologists and
farmers have been fighting a tiny cotton nemesis, the nematode,
for years. The nematode is a flat worm that attacks the plant’s
root system, choking off water and nutrients.

“A very small population can build and build and build,” he
said.
“In a good, wet year, you may not see that dramatic an effect.
But a dry year, you can see if the root system is functioning
well or not.”

Nematodes are hard to control. The farmers’ best tool is
frequently rotating the crops they plant in a field. “But with
less and less land and fewer crops out there to make money,
rotation becomes difficult,” he said.

Diseases in Disguise

Some diseases are masters of disguise. They can look like one
disease but act like something else. One such disease has started
popping up in Georgia peanut fields in recent years.

Funky leaf spot appears to be similar to another leaf spot
disease. But conventional chemicals don’t appear to affect it
much. It hasn’t caused much damage yet.

“But you have to track it down to see if it’s important or
not,”
Kemerait said.

Funky leaf spot acts strangely in another way, too. It seems
to
help another disease in its war on the peanut plant.

One Disease Helps
Another

It causes the plant to drop leaves. The leaves fall to the
ground
and begin to decompose. And this decomposition releases chemicals
that spark another fungus, the one that causes white mold, to
germinate, become more active and attack the plant.

Last year, white mold cost farmers $24 million in damage and
treatment costs. “In combination, (funky leaf) could make white
mold worse each year,” he said.

Farmers can’t relax their war on diseases, he said.

“But if you take our best growers, the ones who do everything
they can right, they generally have the upper hand on the
diseases,” he said.

However, some growers aren’t able to rotate crops. Others are
late applying chemicals or other preventive measures.

“Those are the ones the diseases get the best of,” he said.
“And
once (the diseases) get ahead, it can be difficult to bring them
back in.”