Tifton, Ga. — Plants respond to stresses like drought, disease
and insect attacks in many ways. But one unusual way could lead
to new tools that can help farmers precisely monitor and react
to what’s happening in their fields before a problem gets out of
hand.

Plants can tell you what is happening to them, says Glen Rains,
an engineer with the University of Georgia College of
Agricultural and Environmental Sciences. You just have to figure
out how to understand what they are trying to say.

“Plants do a lot just sitting there,” Rains said.

Unnoticed Damage

Sometimes it’s easy to read what a plant says. But sometimes
it’s hard. It’s hard to know, for instance, if a plant has a
disease attacking it underground. You may not know until the
damage is done.

Some underground peanut and cotton diseases and the damages they
cause can go unnoticed right up until harvest time. Then it’s
usually to late to do anything about it.

But if you know how to do it and have a sensitive enough
instrument, Rains says, you could smell a plant and find out a
lot more about it.

Beneficial Odors

Scientists at the Coastal Plains Experiment Station here and at
U.S. Dept. of Agriculture in Florida have already proven that
when attacked by caterpillars, plants release a chemical odor
that attracts parasitic wasps to the attacked plant.

The wasp then implants an egg into the attacking caterpillar.
The egg hatches, and the larva eats the worm. In fact, different
wasps prefer certain kinds of caterpillars. The plant releases a
different chemical odor depending on the caterpillar attacking
it.

“The question of whether plants evolved to release odors that
attracted insects, or whether the insects evolved to respond to
chemicals produced by the plants is not answered,” Rains
said. “It’s probably a combination of both.”

Rains is taking this research further. If plants release
chemical odors during a worm attack, could they also release
chemical odors during a disease attack?

Well, they do.

Natural Defense

In defense, plants under a disease attack produce chemicals.

“We’re not detecting signals as much as we are detecting by-
products of direct plant defense against the pathogen attack,”
Rains said.

Aspergillus is a fungus that attacks peanuts underground. The
fungus causes aflatoxin, which in certain levels can be harmful
to humans.

But it’s very hard to know where the aflatoxin is in a field.
Peanuts are tested for this fungus after harvest. Small samples
are tested. If the fungus is found, a whole shipment of peanuts
could be segregated. This costs the farmer money at market.

Better to Know

Knowing where the aflatoxin is in a field would help peanut
farmers more efficiently treat the problem, said John Beasley,
UGA CAES agronomist. It would also help come harvest time.

“It would be tremendously important to a farmer,” he said, “to
be able to isolate a field or an area of the field where
aflatoxin is developing and avoid harvesting with the rest of
the peanuts.”

Rains hopes to create a catalog of the different odors plants
produce when attacked by insects or diseases, or when the plant
needs nutrients or water.

Rains envisions a device a farmer or farm worker could carry and
place over plants in a field. The device could “smell” the odors
released from the plants, then reads more accurately what the
plant is trying to say about its condition.