A new scientific report offers hope for controlling Eurasian spotted knapweed, a thistle-studded thug that has overtaken grazing pastures in La Plata County and elsewhere on the Western Slope.

In today?s issue of the journal Science, researchers at Colorado State University say they have learned that the weed poisons soil, but remains immune to its own toxin.

The toxin kills competing plants. Researchers hope the spotted knapweed?s own protective genes might be engineered into other plants so they?re better armed for plant warfare.

Spotted knapweed probably arrived in La Plata County in the 1950s or 1960s, said Rod Cook, the La Plata County weed manager.

To learn more
For more information on spotted and Russian knapweed, call Rod Cook, La Plata County weed manager, at 247-2308, or e-mail cookrd@co.laplata.co.us.

"We?re probably the epicenter for spotted knapweed on the Western Slope," Cook said. "Montezuma County holds the same position for Russian knapweed."

There is a lot of the plant in Archuleta County, too, Cook said. It ranks among the top three noxious weeds in La Plata County as well as the state, he said.

Eradication is difficult, Cook said, because knapweed is highly resistant to herbicides, plowing and burning. There are no biological weapons available, he said.

But the new finding suggests that could change. The finding has immediate value for ranchers and land managers who try to control the weed with herbicide and immediately reseed with a beneficial plant, said Jorge Vivanco, an assistant professor in CSU?s Department of Horticulture and Landscape Architecture.

"What they?ve seen is 99 percent of these plants don?t grow. Now we know why," he said. "You have a toxic compound in the soil."

Conventional wisdom holds that weeds simply out-compete desired plants, hogging water and nutrients by sinking roots deeper and faster, and rising high to grab more sunlight.

When earlier researchers tried to argue that plants also waged chemical warfare against their neighbors, their science was so sloppy that the notion was mocked.

The CSU work puts the topic "back on center stage," Alastair Fitter, a British biologist, wrote in a commentary also published in Science. "Their findings suggest that chemistry may play a large part in successful invasion by certain plant species."

A few dozen weed species, including spotted knapweed, rob Coloradans of $100 million in lost productivity each year. Spotted knapweed, which infests millions of acres in Colorado and millions more across the country, has been called one of the nation?s most economically destructive exotic plants. It thrives above 10,000 feet elevation as well as in the desert around Tucson, where temperatures reach 115 degrees.

The plant was unintentionally introduced to America from Europe in the late 1800s. It depends on seeds for propagation, and it spreads 27 percent a year, Cook said.

Spotted knapweed releases catechin to disrupt the chemistry of would-be neighbors. The toxin attacks vulnerable plants, like American grasses, from the tips all the way to the root. Ultimately, the root cells lose their structural integrity and the plant fails, much like toppling a high-rise building by undermining its foundation.

CSU researchers found that spotted knapweed is among three related species that sow the soil with poison. Scientists are now working on antidotes to the poison.

It?s not clear at which level of the soil the toxin lies or whether its distribution is patchy. If it?s concentrated in upper soil layers, for example, simply plowing or irrigating could move it out of the way.

Reach Staff Writer Dale Rodebaugh at daler@durangoherald.com.