The invasive Thistle and how to mitigate

Thistle is classified as a noxious weed and falls under the Colorado list B species.

What does this mean for you the property owner?

Noxious weed species on lists A, B or C are incorporated into a plan with state noxious weed advisory committees, state governments and other interested parties - to develop and implement management plans to stop the continued spread of these species.

Two types of thistle are list B classifications in Colorado


The Musk Thistle Carduus nutans L.


The Canada Thistle Cirsium arvense (L.) Scop.

The Musk Thistle is a prolific seed producer, Musk thistle can produce up to 20,000 seeds per plant, only one-third being viable. Because Musk thistle reproduces solely from seed, the key for successful management of this noxious weed is to prevent seed production. The Eagle County weed control plan is “Elimination” of this weed by 2020. This thistle forms a dense monoculture by out competing native grasses and plants. It thrives in disturbed habitats where resources are limited and native plants cannot establish or grow as well. Once it establishes itself, it can easily spread with each flower head producing up to 1200 seeds that may last in the soil up to ten years.

The Canada thistle Eagle county noxious weed plan is "Suppression" where the goal is to reduce the vigor of noxious weed populations within an infested region, decreasing its spread to surrounding lands, and mitigating the negative effects of the canada thistle population on infested lands. Suppression efforts may employ a wide variety of integrated management techniques.

What is your responsibility as a property owner if you find these Noxious weeds on your property?

Noxious weeds threaten valuable wildlife habitat and natural resources, cause economic hardships to agricultural producers, and are a nuisance for recreational activities.

The Noxious Weed Act requires all Colorado residents to control noxious weeds using integrated methods to manage the noxious weeds if they are likely to be materially damaging to the land of neighboring landowners.

Reference this portal for more information on the Noxious Weed Act and management plan information

How can you eliminate these weeds from your property?

Musk thistle mitigation

Musk thistle will not tolerate tillage, it can be removed easily by severing its root below ground with a shovel or hoe. Mowing can effectively reduce seed output if plants are cut when the head is in the late-flowering stage. Gather and burn mowed debris to destroy any seeds that have developed.

Canada Thistle Mitigation

Fill an empty spray bottle with vinegar. Do not dilute the vinegar with water

  1. Cut the stem of each thistle plant with a knife.

  2. Spray one to two sprays of vinegar directly on the cut of each thistle plant.

  3. Sprinkle a pinch of salt at the base of each plant.

To eliminate Canada thistle you must injure and exhaust its root system, and do it repeatedly. A successful control program requires multiple seasons, and multiple treatments within a season.

Firstly mowing timed for bud to early-bloom stage and mowing as low to the ground as possible.

Then fall herbicide treatment with Vinegar and salt at the base of the plants is ideal.

These steps may be required for several seasons to fully eliminate this species.

For further information and to protect the beautiful open space in Colorado contact your County weed control program manager for information regarding your local weed management program.