Invasive plant species in Larimer County

Invasive plants are a threat to the economy and environment of Larimer County. These invaders, also known as noxious weeds, originated in other parts of the world and when introduced into this country, have flourished. Invasive stands of noxious weeds threaten our native plant communities reducing species diversity and in doing so, reduce wildlife habitat. Noxious weeds on rangeland and farmland are extremely costly to agricultural producers, either reducing yields or presenting an expensive management need.

Tim D’Amato, Larimer County Weed District

Many examples of “weeds gone wild” can be found in Larimer County such as cheatgrass and Canada thistle. But the worst example of a noxious weed left uncontrolled is leafy spurge. This deep-rooted perennial has become established on many pastures from LaPorte to Wellington and on steep hillsides such as the slopes along Rist Canyon. Eradication of these invaders is not possible now, but hopefully the infestations can be reduced to a more tolerable level and further spread prevented. If awareness had been greater years ago maybe these invaders would have been controlled before becoming the problems we see today.

The introduction of invasive plants is still occurring. Yellow starthistle, which infests many millions of acres across California, Washington and Idaho, can be found on just a few acres in Larimer County. The infestation was recently discovered and hopefully eradication will occur in the next couple of years. Other noxious weeds that have a toehold, but not yet a foothold in Larimer County are Mediterranean sage, spotted knapweed, purple loosestrife and tamarisk.

The Larimer County Weed District is the agency working to minimize existing weed problems in the County, and eliminate new invaders before they take hold. The district assists residents with site visits, plant identification, management recommendations, provides educational information on invasive species and works with residents to be compliant with the Colorado State Noxious Weed Act.

For more information on the Weed District and the services it offers call 970-498-5768 or visit our website at

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