Community Agriculture Alliance: Noxious weeds


— One of the most common misunderstandings about weeds is what qualifies as a noxious weed. When most people think of weeds they picture annoying plants that make their lawn look less than perfect. Dandelions, prostrate knotweed, purslane - all can be a problem when trying to grow a nice turf-grass lawn in the arid West. But none of these pests qualify as noxious weeds. We aren't talking about dandelions, and even crabgrass doesn't make the grade. Noxious weeds are the 900-pound gorillas of plants. They take over meadows, right-of-ways and forests, displacing native vegetation, degrading habitat and ruining hay.

To be considered noxious, a weed must meet certain conditions. The main requirement is noxious weeds are plants not indigenous to North America. Noxious weeds also must meet one or more of the following criteria:

- aggressively invade native plant communities or cropland;

- are poisonous to livestock;

- are detrimental to the environmentally sound management of natural or agricultural ecosystems;

- are carriers of detrimental diseases or parasites.

So why should you care? Noxious weeds have a very negative effect on native plant populations and wildlife, in addition to being costly and time-consuming to manage. One of the worst examples comes from Montana, where elk habitat has been lost at astounding rates to a noxious weed called spotted knapweed. Spotted knapweed releases its own herbicide that kills other plants, and can completely take over a landscape. When an area dominated by spotted knapweed was compared to an area with native weed-free bunch grasses it was shown to reduce elk use 98 percent, increase erosion 192 percent and increase run-off 56 percent.

What is the legal status of noxious weeds? Routt County has its designated noxious weeds - nine weeds picked by a citizen advisory committee as our biggest concerns. Their control is required on private lands. The noxious weeds on the Routt County list are whitetop, leafy spurge, houndstongue, Dalmatian toadflax, yellow toadflax, diffuse knapweed, Russian knapweed, spotted knapweed, and meadow knapweed. If a landowner has any of these species they must manage them. For more information on each species visit: and look under the weed department.

The County's designated noxious weeds aren't the only ones to be concerned about. While our citizen advisory board has picked these as our main focus, the Colorado Department of Agriculture has 18 weeds on its "A" list. The A-list species are species that are serious problems in other parts of the West, but aren't a serious problem in Colorado - yet. The goal is to keep it that way. Because these plants are big problems elsewhere, the state requires these species to be eradicated wherever they are found. Of primary concern in Steamboat Springs, and other Routt County municipalities, are some ornamental plants brought to North America with good intentions. Now that they are here they have escaped from people's yards to become serious pests. Steamboat Springs' residents should especially look for myrtle spurge, cypress spurge, orange hawkweed and purple loosestrife. All four of these species have been sold by a local nursery in the past. To see good pictures of these species check out:, and To see the state's entire noxious weed lists look at

Are these requirements just for private land? No. Under state law the state and counties must manage their lands for these weeds, and under federal law all federal land management agencies are required to manage noxious weeds. We aren't just requiring private landowners to do this. One of the biggest jobs the county faces is managing 951 miles of road right-of-way. Since we have to manage both sides of the road, this translates into roughly 1,900 miles of right-of-way where we manage noxious weeds.

So what can you do about noxious weeds? The next time you pull dandelions in your lawn take a little extra time to look for noxious weeds. When you plant things in your garden, native plants are usually the best choice. If you do plant non-natives, make sure they aren't on the state or county noxious weed list. Even if they aren't on the list, non-native plants should be watched carefully. If they begin to take over your garden or even move out of your garden you should seriously consider removing them entirely. People import plants from around the globe at an astounding rate and there is no guarantee your new plant from South Africa isn't the next spotted knapweed. A great site to check out almost any plant is


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