Friendly Secret Weapon

Spotted Knapweed Has Multiple Benefits

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 horticulture researcher who specializes in plant roots identified and isolated the chemical for the first time. What's more, the chemical is a completely natural and environmentally friendly herbicide that kills other weeds.

The discovery and isolation of the chemical, called catechin, within spotted knapweed may revolutionize the war against weeds.

"For years, scientists have talked about this chemical, but they couldn't find it because it was almost impossible to separate from all the other compounds that naturally occur in soil," said Jorge Vivanco, Agricultural Experiment Station researcher and assistant professor of horticultural biotechnology at Colorado State. "We looked for it in the plant and found that the roots secrete the chemical."

Vivanco and a team of researchers at Colorado State, including postdoctoral candidate Harsh Pal Bais and professor Frank Stermitz, are investigating a wealth of applications for the chemical.

Catechin, which can be extracted in laboratories, acts as a natural herbicide to most other plants, although grasses and grassy-like plants, such as wheat, show 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 and is fatal to spotted knapweed only when artificially inserted into its cells in a laboratory. In nature, spotted knapweed does not permit catechin to re-enter 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 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. The team still is investigating the length of time that it remains active in the soil to prohibit plant growth and how far into the soil the chemical travels after it is released. They also are looking at counter-active chemicals that may be released by other plants, such as plants native to Europe and Eastern Europe, where spotted knapweed originated; many plants native to that area are resistant to catechin.

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 continuously secretes catechin, but immediately begins to produce and release higher quantities of chemicals at the slightest hint of a threat or stress. Just tapping its leaves automatically accelerates the plant's chemical response. This trait could impact how long it takes the soil to recover from the chemical to allow other plants to grow; for example, during stress, such as a drought or an infestation of insects that feed on the plant, more of the chemical may be released and over a longer period of time.