Extension Ag Update
November/December 2002
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Colorado State University Identifies Natural, Plant-Produced Herbicide

Scientist: Jorge M. Vivanco, Horticulture & Landscape Arch Dept, 970-491-7170, Jorge.Vivanco@ColoState.EDU;
Source: Dell Rae Moellenberg, 970-491-6009, Colorado State AgNews DellRae.Moellenberg@colostate.edu

Scientists have speculated for decades that spotted knapweed is able to spread over large areas because of a secret weapon - an ability to release a chemical that kills surrounding plants. Until now, they have never been able to put their thumb on the phenomenon, but recently a Colorado State University horticulture professor identified and isolated the chemical for the first time. What’s more, they are using the chemical as a completely natural and environmentally friendly herbicide to kill other weeds.

The discovery and isolation of the chemical, called catechin, within spotted knapweed may revolutionize the war against weeds for homeowners and farmers. For years, scientists have talked about spotted knapweed releasing this chemical, but they couldn’t find it in the soil because it was almost impossible to separate from all the other compounds that naturally occur in soil, said Jorge Vivanco, assistant professor of horticultural biotechnology at Colorado State. We looked for it in the plant. Spotted knapweed releases catechin into the soil through its roots.

Now that catechin has been identified and isolated, and scientists can capture the chemical in the Department of Horticulture’s laboratory, Vivanco and a team of researchers at Colorado State are investigating a wealth of applications for the chemical. They have discovered that the weed produces two types of catechin that are the same chemical compound but the mirror image of each other in their structure. One has anti-bacterial properties and the other acts as a natural herbicide.

The chemical acts as a natural herbicide to most other plants, although grasses and grassy-like plants, such as wheat, display some resistance to it. This discovery alone holds much potential. For example, it may mean that specific amounts of catechin could be used on lawns to kill weeds without killing grass or on wheat without damaging the crop. The chemical also is environmentally friendly and has existed in the soil for decades.

Catechin kills other species of knapweed, such as diffuse knapweed, which also is a noxious weed. It is fatal to spotted knapweed only when manually inserted into its cells in a laboratory. In nature, spotted knapweed cells do not permit catechin to reenter the plant once the chemical is produced and released into the soil. It is a clever root to produce, secrete and protect itself from this chemical, Vivanco said. There are only small amounts of catechin inside a root at any given time; it secretes it as it produces it.

The Colorado State team has found that spraying catechin on plants or adding it to soil is as effective as 2,4-D against pigweed, lambs quarters and other common weeds. Catechin usually kills cells within the plants in an hour and kills the plants in about a week, but the team still is investigating the length of time that it remains active in the soil to prohibit plant growth. The researchers are working with commercial companies to make spotted knapweed catechin spray available to consumers within a year or two. Colorado State researchers also are working to transfer the genes that produce the natural chemical into other plants to give them a built-in defense mechanism against weeds.

Perhaps one of the most promising applications of the discovery is the fact that spotted knapweed has such a complex defense mechanism. Spotted knapweed immediately begins to produce and release chemicals at the slightest hint of a threat or stress. Just tapping its leaves automatically activates the plant’s chemical response. The funding for these projects comes from Colorado State University’s Invasive Weeds Initiative.

Plants' Odors Can Help Farmers Keep Them Healthy

Scientist: Dr. Glen Rains, Ext. Engineer, Biological & Agricultural Engineering, University of Georgia, 229-386-3377. grains@tifton.cpes.peachnet.edu;
Source: Brad Haire, Editor, College of Agricultural and Environmental Sciences, 229-386-3800

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. 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 too 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.

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. 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.

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 would carry and place over plants in a field. The device could "smell" the odors released from the plants, and then reads more accurately what the plant is trying to say about its condition.