Published on 09/16/02

Plants' odors can help farmers keep them healthy

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.

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