Canada Thistle (Cirsium arvense)

Canada Thistle is an aggressive, creeping perennial that also competes well with desirable range plants and crops.  It can grow in a variety of soils, including some salt-affected soils.  It develops from seeds and from vegetative root buds.  One plant can colonize an area 3 feet to 6 feet in diameter in one or two years.  It often occurs in disturbed areas including ditch banks, heavily grazes areas, tilled fields and other areas.

Dalmation Toadflax (Linaria dalmatica)

Dalmation Toadflax is a perennial that spreads by seed and creeping roots.  The plants are commonly over 3 ft. tall, with light green heart shaped leaves, alternating up the stem.  The flowers resemble Snapdragons and are bright yellow, tinged with orange.  Toadflax has a habit of crowding out more desirable plants.

Diffuse Knapweed (Centaura diffusa)

Diffuse Knapweed is a biennial or short-lived perennial that reproduces and spreads from seeds.  It develops a single shoot, 1 foot to 2 feet tall that branches near the top.  Flower color is usually white but may be purplish as well.  Disturbed areas are prime locations for this weed.  During the first year, these plants form rosettes.  They resume growth early in their second spring, bolt in May or June, set seed in June or July, and die.

Houndstongue (Cynoglossum officinale)

Houndstongue is a biennial, featuring dark red flowers in terminal clusters.  The leaves are velvety, decreasing in width as they ascend the stem.  During the first year, rosettes are formed, while the flowering stalk lengthens in the second year.  Houndstongue is toxic to livestock, containing alkaloids negatively affecting the liver cells.  It also bears seed burs that attach the the coats of animal and thus are easily transported to infest new areas.

Leafy Spurge (Euphorbia esula)

Leafy Spurge is a creeping perennial that reproduces from seeds and root buds.  It is extremely competitive with desirable plants, and has the potential to reduce livestock and wildlife carrying capacities by 50 percent to 75 percent.  Mature plants can range from 1 to 3 feet in height.  They contain a milky white latex that is irritating to the mouths of many grazing animals.  An average of 140 seeds are produced per flowering shoot.  When seeds are ripe, they are expelled at great velocity up to 15 feet away from the plant.  Extensive root systems make this plant difficult to control.

Musk Thistle (Carduus nutans)

Musk Thistle is a biennial weed that aggressively moves into road sides, rangelands, pastures, and other non-crop areas.  The first year, the plants are merely rosettes and do not produce seeds.  The second year is spent producing long shoots with flowering seed heads.  It reproduces only by seed, making it an easier weed to control.  Unfortunately, it can produce up to 20,000 seeds per plant.  It begins to disperse seeds about two weeks after flowering, but plants often have seed heads at various stages of development at any time.  This allows the plant to produce seeds over a long period of time.

Russian Knapweed (Centaura repens)

Russian Knapweed is a creeping perennial that reproduces from both seeds and vegetative root buds.  Shoots and leaves are covered with dense gray hairs.  Shoots are erect and stand from 1-3 feet in height.  Flowers can be pink, lavender, or white.  Its primary means of spreading is from root buds and extensive root system, making this plant a difficult one to control.

Spotted Knapweed (Centaura maculosa)

Spotted Knapweed looks very similar to Diffuse Knapweed but with some exceptions.  It often has purplish flowers rather than the white or diffuse.  The flowering head also has "spots" on it that are not as prevalent on Diffuse Knapweed.  These two species can be managed in similar ways, and they often occur in the same general areas.  Spotted Knapweed infestations are not as severe in Colorado as Diffuse Knapweed, but they do spread rapidly, justifying extra precaution.

Yellow Toadflax (Linaria vulgaris)

Yellow Toadflax is a perennial, sometimes referred to as "Butter-and-eggs."  It resembles the Dalmation Toadflax with the Snapdragon type flowers that are also bright yellow, but differ with a deep orange center.  Yellow Toadflax also grows to 3 feet in height and spreads by seeds and creeping roots.  It has an extensive root system, making it a difficult weed to control.

Hoary Cress "Whitetop" (Cardaria draba)

Hoary Cress is a deep rooted perennial that reproduces from seeds and roots.  Also known as Whitetop, this plant moves into disturbed soils and is highly competitive with other plants.  The leaves are blue-green in color, with a flat white flower that is produced in small bunches common to the Mustard family.

How do these weeds affect YOU?

Noxious weeds are often highly competitive with more desirable forage, particularly in pasture areas where plants of nutritive value are a concern.  Wildlife do not respond well to the consumption of noxious weeds, either and many noxious weeds are toxic to a large variety of animals.  Finally, noxious weeds promote soil erosion and top soil loss, lowering property values.  If you suspect you have any of these weeds on your property, please contact the Chaffee County Weed Department as soon as possible, at 719-539-3455.  If you do not take action on your property, the Weed Dept. is authorized to do so for you and will bill you for their work.

Copyrighted pictures of these weeds can be viewed at the Colorado Weed Managers Association web page at http://www.cwma.org/ under the heading of "Noxious Weeds."