Alex Menard

By Alex Menard

Editor’s note: This article is a response to a letter to the editor published June 9.

What is a weed? There are many ways to answer this question. A weed is a plant out of place. A weed is an unwanted visitor with undesirable features. A weed is a vigorous plant that can take over an area, described by the phrase “growing like a weed.” The suffix “weed” is added to many common native plants, like fireweed, sneezeweed and others.

The word “weed” is also a technical term with a clearly defined meaning. The Colorado State Department of Agriculture protects our natural and agricultural environment by controlling the spread of noxious weeds. The Colorado Noxious Weed Act, established in 1990, accurately states what a noxious weed is. This is done not by a description or definition. A noxious weed is simply one that is included on the state noxious weed list.

The Colorado Noxious Weed Act actually establishes four different subheadings: Lists A, B, C and the Watch List. The purpose is to provide separate management strategies for different plants.

List A contains species which must be eradicated wherever they are found. The plants on this list are uncommon or even unknown in Colorado. For this reason, control is feasible. The undesirable features of these plants are known from their behavior elsewhere. This list could be described as threats which can be controlled. You probably are unfamiliar with most List A plants.

List B plants are already established here. The management strategy is to stop the continued spread of these species. These are plants which you would recognize and should learn to identify and control. Local examples include: absinthe wormwood (Artemisia absinthium), bull thistle (Cirsium vulgare), chamomile (Anthemis cotula), tansy ( Tanacetum vulgare), houndstongue (Cynoglossum officinale), oxeye daisy (Leucanthemum vulgare) and yellow toadflax ( Linaria vulgaris). Remember that the scientific name is used for identification rather than the common name because it is unambiguous. The vulgare and vulgaris species names mean that it is the common variety of that genus.

List C plants are established weeds which may be controlled by the choice of local governments. The state management strategy is to assist local governments, if they choose to try to control the spread of these weeds. You could say that the state does not consider eradication at the state level feasible. There are familiar weeds on this list: burdock (Arctium minus), mullein (Verbascum thapsus), bindweed or morning glory (Convolvulus arvensis) and puncturevine (Tribulus terrestris). Burdock seeds stick to your socks, while puncturevine gives your bike a flat tire.

The Watch List is a new addition, and serves only to identify plants that should be watched should they become problems. The weed list is updated regularly. A county weed list would contain all the plants listed on the state lists A and B, but may differ on List C plants. Some weeds are escaped ornamental plants from gardens and new ornamentals could be added to the list. A very safe strategy for gardeners is to emphasize native plants when planning a new garden.

Dandelion and salsify are not on any list. This is because they are so well established that control is not feasible. Plants like this appear in Colorado flora books and are called naturalized or introduced. They are permanently established parts of our plant communities.

Besides the economic costs of weed control imposed on gardeners, farmers and ranchers, weeds impact our native plant communities. Wildflower lovers should learn to identify and control weeds, which impact the health and diversity of natural landscapes.

Weeds take over a natural community because they can outcompete the natives. This may be because of a lack of natural controls, prolific seed production, a longer growing season or other factors. The most important control factor is prevention.

Weeds get their foot in the door whenever an area is disturbed and not immediately restored. Redstone has very few weeds because Pitkin County regulates and minimizes ground disturbance during construction. In contrast, unregulated Marble has serious weed problems. Disturbance of native vegetation by recreational vehicles provides another opportunity for weed establishment. Tires can carry weed seed to new locations.

The first step in prevention is identification. Your county extension agent can give you a free Noxious Weeds of Colorado handbook, which contains photos and descriptions. There are also weed management guides available online through Colorado State University Cooperative Extension. Learning to identify weeds when they are small makes control easier. 

Want to learn more? The Marble Hub and Marble Museum are cosponsoring a free weed identification and control workshop on July 10 from 1 to 4 p.m. Meet at the Marble Hub.