Noxious weeds have vast, detrimental effects on landscapes and recreational opportunities in Colorado. They do great damage to native ecosystems, contribute to native species becoming endangered and increase wildfire risks.

Noxious weeds are weeds that have been designated by the Colorado Department of Agriculture as being injurious to agriculture, natural habitats, ecosystems and humans. They are weeds that did not originate here; they came to Colorado either because they were unintentionally, or deliberately, released here. Many originated in Asia and Europe, meaning they are not part of successional cycles in Colorado.

“They know no boundaries,” as a release from San Miguel County puts it, “and have no natural predators,” which helps them to spread without restraints. They influence the hydrologic cycle by consuming more water than their native counterparts and reducing water flows in streams.

Tamarix was intentionally introduced into the U.S. to help stabilize stream banks. The species, which consumes staggering amounts of water and increases soil salinity, has spread rapidly throughout this state.

Justin Musser, ecological services manager for Montrose County, calls it a “hot button” species.

“It’s displaced so much of our native habitat” that it’s now become, in effect, a habitat unto itself “that species are dependent upon,” Musser said. “That’s a complicated thing. Tamarix not uses a lot of water and is very salt tolerant. It will sequester salt in its leaves, and when those fall off,” other invasive species will live under them, such as Russian knapweed. “It changes the regime in general,’ Musser said. For that matter, this so-called creeping perennial can grow most anywhere: the weed, which is native to southeast Russia, southern Ukraine, Iran, Kazakhstan and Mongolia, according to CSU Extension’s website, “is not restricted to certain soils and occurs in pastures, agronomic crops, roadsides, waste places and rangelands. Stands may survive 75 years or longer.”

It is toxic to horses.

Noxious weeds also reduce habitat for wildlife species that bring tourist dollars to Colorado: invasive Oxeye Daisy, for example, which is prevalent in many counties, contributes to soil erosion and is not consumed by wildlife. Large infestations encourage big game species to leave an area. “Many tourist attractions state that (the daisy) is a ‘beautiful wildflower,’” San Miguel County’s release states, “and the species is present in some wildflower mixes, making elimination of this daisy hard for managers, due to public perception.”

Cheatgrass, another notorious weed, has invaded rangelands and made them more susceptible to wildfires.

“It ignites easily and spreads quickly,” Musser said, “and after the fire, it’s one of the first things that comes back. I’ve heard presentations from fire scientists who say the 50 to 60 year ‘return interval,’” meaning the time it takes a wildfire to recur, “can be cut to 5-6 years by cheatgrass. It’s outcompeting the native plants and forbs in the sagegrouse’s habitat,” causing the endangered bird to struggle harder for survival.

The Colorado Department of Agriculture keeps a list of noxious weeds species, and how to identify them (find it at Weeds on this list are a prior of San Miguel County’s noxious weed department, which maintains a web page where you can “report a weed” or an infestation. “The more beautiful a weed, the less citizens are moved to take care of the infestation,” the county’s release points out. “Noxious weeds are a growing environmental problem and require persistent management and rapid elimination. Please report noxious weeds to your county weed manager, and remember that ridding Colorado of noxious weeds is a community effort. Do your part!”

For assistance, contact Julie Kolb, the county’s manager of vegetation control and management, via phone (970-327-0399) or email ( Noxious weed management tools for identification can be found at