In the midst of their worst losses ever to tomato spotted
wilt virus, Georgia tobacco
growers need some good news about this killer disease. And
University of Georgia
scientists are certain they have it. Help, they say, is on the
way.

Preliminary results from a second year of studies are
confirming what the first year’s
research revealed. Treating tobacco plants early with a
combination of two chemicals will
dramatically reduce infections of spotted wilt. In fact, it
can
almost eliminate it.

“We’re quite confident of what we have with this
treatment,” said Alex
Csinos, a plant pathologist with the UGA College of
Agricultural and Environmental
Sciences.

One of the products, Admire, is an insecticide already
labeled to control flea beetles
and aphids in tobacco, Csinos said. The other, Actigard, is an
exciting addition that
isn’t yet labeled for tobacco.

Plant Defense
Activator

“We believe it will be labeled for use on tobacco next
year,” Csinos said.
“It’s not a pesticide. It’s a plant defense activator. It
doesn’t kill anything, but
acts much the way a booster shot for flu works with
people.”

Most plants have natural defense mechanisms to ward off
diseases. Actigard boosts those
natural defenses. “It gives the plant the opportunity to
defend itself,” Csinos
said.

Because it’s not a pesticide, it’s an extremely safe
product, too. Labeled in Europe
for use on wheat, grapes and some vegetables, “Actigard
has no effect on
humans,” Csinos said.

Actigard alone greatly reduced spotted wilt in the UGA
research. But the one-two punch
of the two products together was deadly.

Admire, Actigard: Deadly
Duo

The UGA studies were conducted at four locations each year.
Each trial compared plants
left untreated with those treated with Admire alone, Actigard
alone and a combination of
the two.

The scientists gave the treated tobacco seedlings a
“tray drench” treatment
in the greenhouse first. They added three weekly sprays after
the seedlings were
transplanted to the fields.

“At one location, 30 percent of the untreated tobacco
plants were infected with
spotted wilt,” said Hanu Pappu, a UGA molecular virologist
who has worked with Csinos
on the two years of research. “With the Admire treatment,
the rate was 12 percent. It
was 5 percent with Actigard and only 1 percent with the
combination.”

‘Possibility of True
Control’

The second-year figures, Pappu said, are based on plants
with symptoms of spotted wilt.
His exhaustive studies of plant samples will eventually show
the precise percentage of
infected plants, with or without symptoms.

The early results are enough, though, to confirm what the
scientists found in the first
year’s results. In every case, he said, the combination was
better than either product by
itself.

“This gives us the possibility of true control for the
first time,” said Paul
Bertrand, a UGA Extension Service plant pathologist. “All
we’ve had to this point is
some moderate level of suppression of the disease.”

1999 Disease Damage
Heavy

Suppression certainly hasn’t been enough this year.
Bertrand
figures the virus has
killed 35 percent to 45 percent of the state’s tobacco
plants.

Tobacco growers are allotted a certain number of pounds of
“quota” leaf they
can grow. They usually plant 10 percent to 20 percent more
than
that to be certain they
can make their quota. But the buffer hasn’t been big enough
this year.

“More tobacco farmers are filing for crop insurance
than in the past 10
years,” Bertrand said. “The crop isn’t in yet, but I
suspect that 50 percent to
60 percent of the growers won’t make their pounds.”

Drought and other diseases have hurt the crop, too.
“But spotted wilt is
responsible for 80 percent of the shortage,” Bertrand
said.

Could Save Millions of
Dollars

In 1997 — the worst year yet — spotted wilt cost Georgia
growers $12.7 million, or
about 8 percent of the $158 million crop. This year, the
losses
could be much higher.

Had growers been able to use the Admire-Actigard treatment
this year, though, losses
could have been much lower. “If these studies held true,
we’d be looking at a
5-percent to 10-percent stand loss and no loss of pounds,”
Bertrand said.