What are Noxious Weeds and Why are they a Nusiance?

“Noxious weed” means an alien plant or parts of an alien plant that have been designated by rule as being noxious or has been declared a noxious weed by a local advisory board, and meets one or more of the following criteria:

(a)  Aggressively invades or is detrimental to economic crops or native plant communities;

(b)  Is poisonous to livestock;

(c)  Is a carrier of detrimental insects, diseases, or parasites;

(d)  The direct or indirect effect of the presence of this plant is detrimental to the environmentally sound management of natural or agricultural ecosystems.

Noxious weeds impose a wide variety of negative impacts on people, wildlife, and the environment.   Livestock production and crop yields can be greatly reduced as well as adding the significant costs of weed management.  Noxious weeds can also reduce the value of land when infestations are severe.

Noxious Weed Categories

Plants are prioritized as List  A, B, or C species by the Colorado Department of  Agriculture (CDA).

List A:  Rare noxious weeds that must be eradicated statewide.

List B:  Discretely distributed noxious weeds that must be eradicated, contained, or suppressed, depending on their location, to stop their continued spread.

List C:  Widespread and well-established noxious weeds in Colorado; control is recommended by the state and may be required by local government.

 For more information on noxious weeds:   http://www.colorado.gov/ag/weeds

How Can Noxious Weeds be Managed?

Prevention: The most effective, economical, and ecologically sound      management technique.  The spread of noxious weeds can be prevented by cleaning equipment, vehicles, clothing, and shoes before moving to weed-free areas; using weed-free sand, soil, and gravel; and using certified weed-free seed and feed.

Cultural: Promoting and maintaining healthy native or other desirable   vegetation.  Methods include proper grazing management (prevention of overgrazing), re-vegetating or re-seeding, fertilizing, and irrigation.

Biological: The use of an organism such as insects, diseases, and grazing     animals to control noxious weeds; useful for large, heavily infested areas.  Not an effective method when eradication is the objective, but can be used to reduce the impact and dominance of noxious weeds. 

Mechanical: Manual or mechanical means to remove, kill, injure, or alter growing conditions of unwanted plants.  Methods include mowing, hand-pulling, tilling, mulching, cutting, and clipping seedheads.  

Chemical: The use of herbicides to suppress or kill noxious weeds by disrupting biochemical processes unique to plants.

Noxious Weeds in Manitou Springs

(Click on the name for more information)

Bouncingbet

Bouncingbet: The flowers are crowded at the ends of branches, and have five petals that are generally light pink to white and slightly notched at the apex. Flowering begins in July and continues until September. Bouncingbet can be poisonous to livestock and humans. The habitat of Bouncingbet is often found in large dense patches on hillsides, along rivers, roadsides, meadows, and waste areas. Bouncingbet is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.

 Common tansy

Common tansy: Yellow flowers are numerous in flat-topped dense clusters at the tops of the plants. Button-like flower heads lack ray flowers. Flowering typically occurs from July to September. The leaves are alternate, deeply divided into numerous narrow, individual leaflets. Mature plants are 1.5 to 6 feet tall. Habitats for Common tansy include along roadsides, streams, irrigation ditch banks, waste places, ornamental beds and in pastures. Common tansy is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.

Cypress spurge

Cypress spurge: Leaves are linear, approximately 1/2 to 1 1/4 inches long and 1 to 2 mm wide. Upper stem leaves that occur near the inflorescence are yellow or yellowish-green in color. Leaves are stalkless, alternate, narrow and linear to lance-shaped. Stems are 4 to 32 inches high, hairless, green to yellowish green in color and branch in the upper portions. The leaves and stems emit a milky, toxic sap when broken. Humans should be careful and avoid contacting the plant with bare skin as it can cause skin irritation for some people. Cypress spurge is designated as a “List A” species in the Colorado Noxious Weed Act. It is required to be eradicated wherever found in the State.

Dalmatian toadflax

Dalmatian toadflax:  A single plant produces 500,000 seeds, most of which fall within 18 inches of the parent plant. Seeds can remain viable for at least 10 years. Dalmatian toadflax grows to 3 feet, and has bright yellow snapdragon-like flowers with an orange throat on elongated racemes. The alternate leaves are broad, with a thick, waxy cuticle and a bluish cast. Each leaf is heart-shaped and wraps the stem. Habitats for Dalmatian toadflax include disturbed open sites, fields, pastures, rangeland, roadsides, cropland and forest clearings. Dalmatian toadflax is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.

Dame's rocket

 Dame's rocket: The flowers are white to purple with four petals and are clustered in loose terminal stalks. Flowers appear from May to August and the plant can produce seeds and flowers on any flower cluster at the same time. Leaves are slightly hairy, alternate, and 2 to 4 inches long. The leaves are lance shaped with toothed margins. Habitats for Dame’s rocket include: gardens, partly shaded woodlands, ditches, roadsides, pastures, rangelands, thickets, open woods, disturbed sites, and other areas that have moist well drained soils and full sun to light shade. Dame’s rocket is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.

Houndstounge

Houndstounge: Flowers are reddish-purple (occasionally white) and droop slightly from densely clustered panicles. The five rounded petals are cupped by five sepals covered with long, soft white hairs. Flowering occurs May to July. The simple leaves are lance or oblong shaped, with a smooth edge and no teeth or lobes. Leaves are alternate, 1 to 12 inches long and 1 to 3 inches wide. The leaf tip is sharply pointed, like a hound’s tongue, yet are covered with long-soft white hairs. Houndstongue is poisonous. Toxic pyrrolizidine alkaloids in Houndstongue stop liver cells from reproducing. Though the plant has a distinctive odor that repels animals, it is more palatable when dried. Houndstongue is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.

 Knotweeds

Knotweeds: Are bright green, bamboo-like, perennial plants that grow 5-16 feet tall and spread through lateral root systems (rhizomes). Stems are hollow between nodes, and often reddish-brown and swollen at the nodes. Japanese knotweed leaves are broadly ovate or spade-shaped with low, bump-like scabers on the underside instead of hairs. Giant knotweed leaves are heart-shaped with long hairs underneath, and Bohemian plants typically have both leaf forms. The small, showy, greenish-white flowers develop on branched clusters and are present in late summer. Like other species in the genus Polygonum, the soil seed reserve is likely long-lived, and site monitoring should be carried out for at least ten years after the last flowering adult plants have been eliminated. All three knotweeds are designated as “List A” species in the Colorado Noxious Weed Act. They are required to be eradicated wherever found in the state.

Myrtle spurge

Myrtle spurge: The leaves are fleshy, blue-green and alternate. Flowers are inconspicuous with yellow-green, petal-like bracts that appear from March to May. Myrtle spurge contains a toxic, milky sap which can cause severe skin irritations, including blistering. This plant is poisonous if ingested; causing nausea, vomiting and diarrhea. Wearing gloves, long sleeves, shoes, and eye protection is highly recommended when in contact with myrtle spurge, as all plant parts are considered poisonous. Myrtle spurge is designated as a “List A” species in the Colorado Noxious Weed Act. It is designated for statewide eradication.

Oxeye daisy

Oxeye daisy: It is an erect, rhizomatous, creeping perennial that grows 10 inches to 2 feet tall. The basal and lower leaves are lance shaped and toothed with long petioles (leaf stem) and the upper leaves are narrower and clasp the stem. The leaf size progressively decreases up the stem. Flower heads are mostly solitary at the end of the flower stalk and the flower head has 15 to 30 white ray flowers. Habitats for Oxeye daisy included meadows, native grasslands, pastures, waste grounds, railway embankments, and along roadsides. Oxeye daisy typically grows in high elevations in Colorado. The site must be monitored for at least 10 years after the last flowering adult plants have been eliminated and treatments repeated when necessary. Oxeye daisy is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be either eradicated, contained, or suppressed depending on the local infestations.