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Knapweed Chemical May Be Basis Of 'Green' Herbicide

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 structure (called enantiomorphs). 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 the 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.

Funding for these projects comes from Colorado State University’s Invasive Weeds Initiative. - By Dell Rae Moellenberg

[Contact: Dell Rae Moellenberg]






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