Noxious Weed Information

2021 Pitkin County Weed Logger Map

We have a new public service in Pitkin County!  Pitkin County hires a contractor to use chemical controls on designated noxious weeds in county road right-of-ways every summer.  The green lines show the route of the spray truck.  Zoom in on your neighborhood to see the purple shapes - this means herbicide was sprayed on noxious weeds in that area.  This map shows all 2021 chemical control activity.  For more information, email us at

What is a Noxious Weed?

The term "Noxious Weed" is a political (rather than scientific) designation given to a plant that is non-native to North America and has aggressive, invasive tendencies in our area, giving it the potential for serious economic, agricultural, and/or ecological damage.  Often these weeds are kept in check by natural controls (e.g. predators, environmental conditions, etc.) in their native territory.  However, lacking such controls in our area, these plants are able to propagate very aggressively, allowing them to crowd out native plants and dominate local plant communities. 

 What is the Colorado Noxious Weed Act?

The Colorado Noxious Weed Act and its governing Rules and Regulations state that certain noxious weeds pose a threat to the continued economic and environmental value of the land in Colorado, and that they must be managed by all landowners in the State, both private and public. 

These statutes also require the local governing authority to adopt and administer a noxious weed management program aimed at reclaiming infested acres and protecting weed-free land.  The Act directs local governments to take the steps necessary to manage noxious weeds in their respective jurisdictions, and grants them authority to enforce the Act.

In accordance with these statutes, Pitkin County has established a Weed Advisory Board,  a Noxious Weed Management Plan, and a Weed Management Enforcement Policy. 

 What if my neighbors don't control noxious weeds on their property?

When it comes to weed control, It is important that we all be good neighbors because weeds know no property boundaries and easily spread in the wind, across fence lines, down ditches, and on animal fur and tire treads. However, many people are still unaware of their weed management responsibilities. Thus, the first step is to make sure your neighbor knows about the infestation on their property and that it is their  responsibility to comply with both Colorado and Pitkin County law. We have found that most people will voluntarily take appropriate action to control the spread of invasive plants on their property once they become aware of the problem.  

Pitkin County prefers cooperation with landowners to formal enforcement.  We are available to assist landowners with identifying weeds on their property and developing a satisfactory weed management plan. 

In cases of non-compliance, local governments do have authority to enforce the Colorado Noxious Weed Act.  This can include obtaining a warrant to enter the property, perform weed management, and assess the costs of management as a lien on the property.  Visit the Enforcement page for more information.

 Who pays for weed control?

Landowners are responsible for the costs of weed control on their property, unless other specific arrangements are made with lessors or land-users.  

 How can I get help identifying weeds on my property?

There are various resources available to help you identify noxious weeds and develop a weed management plan.  The Pitkin County Land Management Office has a variety of publications available for you to pick up if you would like a hard-copy. 

 Many Resources are available on the web:

Land Management Staff are also happy to visit your property and help you identify plants in person.  Contact the office at 970-920-5390 or by email to

What should I do if I find noxious weeds on my or someone else's property in Pitkin County?

If you know the landowner, try to educate them about weeds and direct them to some of the resources on our website.  Often people are simply not aware of their weed control responsibilities, and can be more responsive to someone they know personally.  If the matter is neighborhood-wide, see if your HOA or Caucus can help educate the neighborhood. There may already be policy in place to deal with infested properties.  By dealing with the problem directly, you may get a much timelier response than by utilizing the County's formal enforcement procedure. 

Nevertheless, part of our responsibility is to enforce the Weed Law in Pitkin County.  If you do not know the landowner or are unable or unwilling to talk to him/her directly, do not hesitate to report the infestation to the respective local governing body:

Pitkin County: 970-920-5390 or

City of Aspen: 970-429-2031 or

Town of Snowmass Village:  970-922-2240 

I have introduced biological controls to control an infestation.  Can the County still require additional control measures?

Yes, potentially.  While Pitkin County appreciates all efforts to control noxious weeds, landowners must provide effective control. It is a good idea to check the biological control method you are using with your local weed control agency.   Many effective biological controls do exist, but proper application is key.

 How can I help prevent the spread of noxious weeds?

  • Learn to identify the plants in the area where you live and work.
  • Manage noxious weeds on your property and share your concerns with neighbors.
  • Minimize activities which cause disturbance to the ground and to established vegetation.  Do not allow overgrazing on your land.
  • Re-vegetate disturbed areas with native grasses and forbs. 
  • Avoid using soil or materials that come from weedy places.  Try to get certified weed-free seed, dirt, gravel, and mulch.
  • Report the location of new noxious weed species to your local agency so that they can be mapped and eradicated swiftly.
  • Always use integrated pest management techniques to ensure thorough and safe management practices.
  • Use native species for landscaping as these plants are less likely to be overly invasive.
  • Utilize good land management practices such as proper irrigation and fertilization, erosion control, rotational grazing, re-vegetation, and maintenance of competitive (preferably native) vegetation.