The Larimer County weed management program strives to minimize the occurrence of weeds and associated negative impacts on native plant communities, agricultural lands and public corridors in Larimer County. In doing so, staff members work to establish and maintain relationships within the community based on best land stewardship practices. Staff members achieve this through collaborative research and discourse, making themselves and their resources accessible to the public and offering continuing education for the general public, as well as land stewardship professionals.


  • Assist landowners with noxious weed problems through plant identification, weed management recommendations and development of vegetation management plans
  • Promote noxious weed education and awareness by way of community presentations, site visits and tours of collaborative field research plots demonstrating best management practices
  • Manage noxious weeds on County property and roadside rights-of-way
  • Enforce the Colorado Noxious Weed Act on non-compliant property owners

Need Help Identifying a Weed?

Send us a photo of a weed you find in Larimer County and our staff will help you identify it.

A weed is often defined as 'a plant out of place'. This simple definition can refer to many different plants in many settings. A 'noxious weed' has a special definition with a legal connotation. The Larimer County Weed District follows the guidelines of the Colorado State Noxious Weed Act which defines 'noxious' weeds as plants that are exotic and invasive. Exotic means non-native, or weed species that originated in other parts of the world. Most of the weed species considered noxious in Colorado originated in regions of Europe and Asia with a climate similar to the Rocky Mountain Region. Invasive plants are those vigorous enough and competitive enough to crowd out desirable plants, and in doing so, decrease native plant diversity and wildlife habitat. The increased vigor and competitive ability of a non-native plant is the result of being introduced into a country with different grazing animals, predatory insects, disease and other limiting factors that kept the species in check in its native land.

The Colorado State Noxious Weed Act lists 71 weed species considered to be a threat to the economy and environment of Colorado. Another 24 species are listed on the state's Watch List. The lists are categorized by priorities:

  • List A species are of the highest priority. These weeds are not well established in Colorado, are potentially a large problem to this state, and require mandatory eradication by local governing agencies. There are seven List A species in Larimer County.
  • List B species are common enough in parts of the state that eradication is not feasible, though the species are still recommended for eradication, suppression, or containment depending on distribution and densities around the state. The County has 16 of these species on the Larimer County Weed List.
  • List C species are widespread and well established.
  • Watch List species are weeds that are on this list to educate and encourage identification and reporting. They are determined by:
    • Not known to occur in the state but their noxious characteristics are found in the region.
    • They have been found to display noxious characteristics in plant communities similar to those in Colorado.
    • They have noxious characteristics as determined by the plant assessment process used by the state, yet their distribution and effect on lands in the state is still unknown.

The Larimer County Noxious Weed Management Plan requires eradication of all List A species, as mandated by the state, and containment and suppression measures for 16 of the List B species identified as significantly troublesome in Larimer County. County outreach programs emphasize identification and management of the 16 List B species but the Weed District reserves the right to enforce on any state-listed noxious weed if infestation size and density deems it necessary. Other species, too common to require control, are still considered troublesome weeds in the County and the Weed District will provide best management practices. The Weed District has also compiled a list of native and non-native plants that are often a concern with Larimer County residents that can be found in Frequently Asked About Pasture Plants. For a comprehensive listing of weeds and to see a summary of the weed law go to the Weed Law Summary and Weed Lists page.

The Larimer County Weed District encompasses the eastern one sixth of the county (see District Map). Funding for the District is provided by a mill levy paid by residents within the District boundary. Activities conducted outside the Weed District are supported through an enterprise program that obtains funds from contracted weed management work with private landowners, federal, state, and local agencies and from state and federal grants. It is the goal of the District to eventually expand and encompass all of Larimer County. Expansion would require voter approval through a ballot initiative or referendum, and will be proposed in the near future.

Weed District History

A group of farm leaders under the direction of the Extension Director initially laid the groundwork for the formation of the Larimer County Weed Control District in 1959.

The Fort Collins Weed District was formed March 2, 1960. The Loveland Weed Control District was formed about a month later on April 13. The lands that these districts encompassed are in the collection of documents and files in the Larimer County Courthouse Archives.

The two districts were formed as part of a pilot program, which was to last three years, to control Canada thistle. Landowners outside the pilot districts saw just how successful the program was in combating Canada thistle, and they petitioned to form another district, which would include more of the County's land.

At first, some committee members wanted to include the rest of the County in its entirety. This was voted down because of the vast areas of range and forest lands. The final decision was to include Canada thistle control on all irrigated lands within the Northern Colorado Water Conservancy District. Thus, the East Larimer County Weed Control District was formed April 19, 1962.

In addition, the two pilot districts petitioned for an extension of their termination date in November 1962. A new termination date was set for December 31, 1966.

In February 1967, the Advisory Committee members of the three districts petitioned to dissolve the districts and consolidate them into one. On March 1, 1967, the three districts became the Larimer County Weed Control District.

The original districts were formed using the parameters of The Pest Act, Ch. 6, Art.16, CRS 1953. The Larimer County Weed Control District now operates under 35-5 CRS 1973 and 35-5.5 CRS 1990.

After leafy spurge was declared a noxious weed by the Commissioner of Agriculture of the State of Colorado, it gained noxious weed status by ballot in the Larimer County Weed Control District in April 1979. Over the years, fifteen other weeds have been designated noxious in Larimer County, bringing the Larimer County noxious weed list to its current total of sixteen.

The districts were originally funded out of the County general fund. In 1982, the County attorney began to look at the option of a special mill levy to fund the District. Today, the Weed Control District is funded by a mill levy assessed landowners within the District boundaries. According to 35-5 CRS 1973, the mill levy cannot exceed 2 mills. The District now operates on a budget funded by a mill levy in the range of .143 mills. With the passage of the tax limitation bill, Amendment I, this will probably be the maximum mill levy allowable.

Bylaws for the Weed Control District were proposed and in November 1993, accepted by the seven member Advisory Committee.

The current Weed District consists of five full-time employees: a Land Stewardship Manager, a Senior Weed Specialist, and three Weed Specialists. During the busy season from April - October, several seasonal employees fill a variety of roles. The staff itself brings over fifty years of dedication to Larimer County and to the Weed District in particular. Our experience and backgrounds encompass a diverse history of expertise in weed management and land stewardship. We draw upon this experience to provide landowners with services that are designed to educate and propagate our mission of community involvement. We are constantly keeping ourselves abreast with the latest changes in land stewardship practices through continued education and research. Much of the research consists of weed management demonstration plots set up cooperatively with the Weed Science group from Colorado State University.

The Larimer County Land Stewardship Advisory Board consists of seven members appointed by the Board of County Commissioners. The purpose of this Committee is to serve as a sounding board for overall weed control policy and forestry issues, and to represent county constituents on issues for the Board of County Commissioners. The Land Stewardship Advisory Committee is advisory only. District weed and forestry control policy is made by the Board of County Commissioners and staff.

The Advisory Board meets with the Larimer County Land Stewardship Manager (who serves as the Weed District Supervisor) and County Forester every three months. These quarterly meetings are also attended by the Department of Natural Resources Director and one of the County Commissioners, appointed as liaison to the Board. The meetings consist of updates presented by the weed supervisor and forester, followed by a presentation of current issues relating to the Larimer County Weeds and Forestry are discussed.

Meetings are held every three months in the Lake Loveland Room of the Larimer County Courthouse, 200 W. Oak St. in Ft. Collins.

Agenda items for the Weed Advisory Board are determined by the Board's recommendations, past discussions and citizen input. The agenda is usually determined 7-10 days before the scheduled meeting. If you have any questions, comments or to add an item to the agenda, please contact Casey Cisneros at (970) 498-5769 two weeks prior to the scheduled meeting time.

The weed management of county maintained rights-of-way is the responsibility of the Larimer County and mandated by the Colorado Noxious Weed Act. Property owners requesting no spray are responsible for noxious weed management within that zone. Failure to comply will result in Larimer County resuming spraying operations. The posting requirements listed below must be met if the County is to honor a request to refrain from treating an area with herbicides.

  • Signs must be posted immediately adjacent to the rights-of-way but not on the rights-of-way.
  • Signs must be posted at each end of the property; spraying operations will end at the point where the first sign is posted and begin at the point where the second sign is posted.
  • Signs must be clearly visible to approaching traffic from the road; they must be at least 36 inches above the ground and not obstructed from view.
  • Signs and the lettering on them must be large enough to be easily read from 20 yards distance.
  • Requests need to be submitted annually.

To request County Road No Spray areas, please call us at (970) 498-5768, or submit your request using the link below. You will need to create an account in the online portal first before submitting your request.

Submit a Do Not Spray Request

Larimer County Weed District

OFFICE: 2649 E. Mulberry St., Suite 6, Fort Collins, CO 80524
PHONE: (970) 498-5768
OFFICE HOURS: 8 a.m. - 4 p.m., Monday - Friday (except holidays) Please call ahead for an appointment.