Noxious Weeds

Diffuse KnapweedNoxious weeds are non-native plants that displace native plants or out-compete native plants for soil moisture and degrade natural habitat. Many noxious weeds are undesirable to cattle and wildlife, and can even be toxic, thereby reducing available forage habitat. It is important to manage noxious weeds in our area through identification, prevention and control of infestations.

Noxious weeds can be introduced through seeding, as ornamental escapes or can establish in disturbed areas (roadsides, overgrazed pastures, construction areas) as well as riparian corridors and wetlands. To control or prevent infestations and educate landowners, the state-wide Colorado Noxious Weed Act (PDF) (35-5.5 Colorado Revised Statutes (CRS)) was established to identify a noxious weed list and prioritized management goals. The state's noxious weeds are grouped into three different lists, A, B and C. This categorical listing of a noxious weed plant as A, B or C will dictate whether it is to be eradicated, contained or controlled.

Noxious Weed Act

In an effort to control or prevent noxious weed infestations, the State adopted the Colorado Noxious Weed Act as included in Title 35 of the Colorado Revised Statutes. The law requires all Colorado residents, including local land managers, control noxious weeds using integrated methods to manage those noxious weeds. View additional information on the statewide Noxious Weed Program administered by the Colorado Department of Agriculture.

According to the Colorado Noxious Weed Act, municipalities have certain responsibilities that include:

  • Establishment of a local advisory board
  • Adoption and administration of a noxious weed management plan
  • Treat public lands, including rights-of-way, to impede the spread of noxious weeds

Current Town Practices

The Town's Parks Division actively manages noxious weeds found in parks and open space lands within Castle Rock boundaries. Staff utilizes an integrated process consisting of mowing, spraying, pulling, utilization of native landscaping and biological controls. In the past, the Town has utilized volunteers to assist with weed management and has also released weevils in Town parks and open space that feed on knapweed. Other areas of concern include undeveloped lots or lots that have been graded in preparation for development. Graded land removes the top layer of soil and nutrients providing an opportunity for noxious weeds to invade. Other areas of concern are rights-of-way and drainage areas throughout Town.

Noxious Weed Board

Municipalities such as Castle Rock, may have one of their boards or commissions, such as our Parks and Recreation Commission, meet as a Weed Board in order to conduct its business without creating another board. The Parks and Recreation Commission was presented with this option at the January monthly meeting and Town Council provided approval by resolution on February 2, 2021 (PDF)  to revise the existing Commission duties to include the formation of an Advisory Board as an auxiliary function.

Responsibilities of the Weed Board include:

  1. Develop recommended integrated weed management criteria and plans for managing priority noxious weeds
  2. Declare noxious weeds and any state noxious weeds designated by rule to be subject to integrated management
  3. Prepare and recommend to Town Council a weed management plan
  4. Review the management plan at regular intervals but at a minimum once every three years

Noxious Weed Management Plan

Town staff, led by the Parks and Recreation Department, drafted a Noxious Weed Management Plan (PDF) that was approved by the Weed Advisory Board and Town Council in April 2021 and May 4, 2021 respectively. This plan includes an overview of the Colorado Noxious Weed Act, management options/approaches, implementation of the plan, public education and ongoing program evaluation. This management plan (PDF), including overall compliance with the Colorado Noxious Weed Act, is applicable to both public and private properties.

Town Municipal Code Update

Upon completion of the Noxious Weed Management Plan and approval by Town Council, changes were made to section 8.12 of the Town's Municipal Code in order to properly reference noxious weed management requirements according to the Noxious Weed Act, including weed growth limitations, property owner responsibilities, enforcement and the duties of the Advisory Board. Currently, the Municipal Code limits growth of weed height to 12 inches or less, which serves a fire prevention purpose rather than a noxious weed control function, and it is the responsibility of the property owner to manage weed height on their respective property. The updated Code also specifically references the Colorado Noxious Weed Act and the Noxious Weed Management Plan.


Noxious weeds can be managed by using a combination of control methods including mechanical, cultural, biological, preventive and chemical, but since they grow or spread differently, not all methods will be effective on all weeds. Refer to the Colorado Department of Agriculture for required controls. Consult with Douglas County Weed Control for specific recommendations for eradication, containment or control. It is important to properly identify noxious weeds and use diverse control methods to reduce or eradicate infestations.

The Town Parks and Recreation Department, Public Works and Castle Rock Water utilizes integrated management techniques to actively manage noxious weeds on Town-owned properties, including parks, trails, open space areas, well sites and public right-of-way. Mowing, hand pulling, native grass restoration, herbicides and biological control agents are all examples of integrated management techniques used by the Town.

The Town does not spray herbicides indiscriminately but rather uses a spot spray approach for heavy infestations of weeds and only use low-toxicity chemicals that are not restricted. Additionally, the Town has found success utilizing releases of biological control agents, seedhead and root-boring weevils, to control large infestations of Diffuse Knapweed on Town-owned open space properties.

Castle Rock residents are encouraged, and required by both Town Municipal Code and state statute, to control noxious weeds on their property. Please reference our noxious weed identification page to help identify any noxious weeds that may exist on your property along with management best practices suggestions.

What You Can Do To Help

  • Prevent - Eradicate - Control
  • Learn about noxious weeds in Colorado
  • Familiarize yourself with the noxious weeds in your area
  • Work with your neighbors to identify the extent of weed populations
  • Landscape with plants native to your area

Helpful Links