Creating A Natural Herbicide

An invasive weed that has taken over vast swaths of grazing land in the West may hold the key to creating an effective, natural herbicide.

A Colorado State University study found that a chemical compound secreted from the roots of spotted knapweed is toxic to surrounding plants and has potential to wipe out other unwanted weeds.

"This is a herbicide that is as potent as a commercial chemical but it comes from a natural plant," said study author Jorge Vivanco, an assistant professor of horticulture biotechnology at CSU. "It's considered an environmentally friendly herbicide."

Vivanco's research - and a separate study at the University of Colorado in which bugs stopped the spread of diffuse knapweed - are among the latest efforts to find natural ways of controlling invasive plants that have bedeviled farmers and ranchers for centuries.

Eric Lane, who carries the unlikely title of "state weed coordinator," says there is a growing emphasis on nonchemical ways to fend off weeds. He called the knapweed study exciting because it would encourage others to try similar efforts.

At least three knapweed species are found in Colorado, and forms of the invasive weed have taken over millions of acres in the West. The plant is capable of wiping out all other surrounding plants, effectively ruining grazing lands. Because they are not native to Colorado, they have few predators.

Originally from eastern Europe and western Asia, the most common knapweed species in the West are believed to have arrived in the late 1800s in contaminated crop seed or possibly discarded soil from ships.

Common forms feature tiny white or purple flowers on spindly, leafed green stalks.

Two years ago, Vivanco read about a knapweed species that invades and colonizes by secreting a toxic compound into the soil through its roots.

His team tried to become the first to isolate the chemical from spotted knapweed - a feat complicated by the complex jumble of contaminants, microbes and chemicals found in soil.

The team grew spotted knapweed plants in flasks in the lab. The roots were submerged in a water-based solution while the plant floated on top.

The plants secreted the toxic chemical compound into the liquid, making it easier for the researchers to isolate each compound in it.

They found nearly 30 compounds, including two forms of catechin. One type had antibacterial properties and the other had a toxic effect on other plants.

The researchers found that spraying toxic catechin on plants or adding it to soil was as effective against some weeds as common synthetic herbicides, typically killing the plants within a week.

Vivanco said no one previously knew about catechin's toxic effect on plants.

His findings were published in last year in the journal Plant Physiology.

Because there is no evidence that catechin is toxic to humans or animals, Vivanco hopes it will eventually be fast-tracked for approval by the Environmental Protection Agency.

CSU has licensed the catechin technology patent to a company, and Vivanco hopes to see it on the market in two or three years.

Ragan Callaway, an associate professor of biology at the University of Montana and a plant ecologist who specializes in invasive weeds, said Vivanco's research is exciting but should be carefully studied.

"Just because it's produced organically doesn't mean it won't kill you. On the other hand, I think that because Jorge is trying to use natural processes to control how plants interact with each other is fantastic," Callaway said.

Vivanco said the discovery has several potential applications as a herbicide. In reduced concentrations the chemical only kills select plants while sparing others. That could allow farmers to protect a crop while killing a weed. Or it could be used as a preventive agent by mixing it with soil before weeds emerge.

By Katherine Vogt