Noxious weeds are aggressive non-native plants that invade an area, displacing native vegetation and reducing agricultural productivity. These invasive plants can threaten wildlife habitat and recreational use of your land. Both the State of Colorado and individual Counties have specific regulations on noxious weeds. They also provide helpful guides and resources for identifying and controlling these weeds.

Within the Lefthand, St. Vrain, Big Thompson and Little Thompson watersheds, noxious weeds can range from Russian Olive, a thorny tree that can form thick clumps replacing native trees, to Canada Thistle, a very aggressive species that forms dense stands on stream banks and in fields. Noxious weeds should be controlled using integrated methods that are effective and minimize harm to your land and surrounding neighbors’ land. These methods are described in detail in the ‘Weed Identification and Management’ section of Chapter 2 and in the stewardship and recovery strategies in ‘Chapter 3: Stewardship and Recovery Strategies’.

State Noxious Weed Regulations

Because of the harm noxious weeds can cause to native ecosystems and agricultural lands, the State of Colorado has implemented the Colorado Noxious Weed Act (Act). Under this Act, the Colorado Department of Agriculture (CDA) has implemented a noxious weed control program. The aim of this program is to prevent the introduction of new invasive species, eradicate species with isolated or limited populations and manage well-established and widespread noxious weeds. The CDA produces lists of noxious weeds categorized by severity of invasion and potential threats. These lists are reviewed every year and can be found on the Colorado noxious weed program web page.

County Weed Control Management Programs

Every Colorado county (and many cities and towns) has a weed control program. Each weed control program works closely with the CDA and manages noxious weeds through education and development of noxious weed management plans specific to the needs of the county. Contact information for your county’s weed program can be found on the Colorado noxious weed program web page

Boulder, Weld and Larimer County weed program websites are below:

CDA Noxious Weed Resource

Boulder County Weed Program

Weld County Weed Program

Larimer County Weed Program

Identifying Noxious Weeds

The Colorado Noxious Weed Program has fact sheets with descriptions and photos for most of the noxious weeds listed by the state. You can find examples of these fact sheets for some of the noxious weeds you are most likely to encounter in the ‘Weed Identification and Management’ section of Chapter 2. All of the fact sheets are available on the CDA website. Your county weed manager would also be able to provide additional information for identifying noxious weeds.

Colorado Noxious Weeds Mobile App

by State of Colorado