Noxious Weeds

    Weeds are native or non-native plants that are unwanted in a particular area at a particular time. Change the area and the time and the plant might be desirable and cultivated.
     When weeds become so wide-spread that they threaten crops, livestock, or native species, they may become more than just a "weed". They may then find themselves on a state list of plants to be attacked in a methodical manner with state support. They might then be termed "noxious weed", "invasive species", "exotic species", "alien species", or some similar term as set forth in law by each governing body.
     These noxious weeds find their way into new areas via boats, planes, soles of shoes, imported animals and agricultural products, etc. With increasing frequency, these most dangerous of weeds are causing the extermination of native flora and fauna from larger and larger areas; they are also causing huge economic loses to range and crop lands; and they are also causing significant environmental damage because herbicides are often used to combat them.

     According to the 6h edition of "Troublesome Weeds of the Rocky Mountain West", prepared by the Colorado Weed Management Association,

     "Biodiversity and ecosystem stability are threatened by noxious weeds. A common characteristic of all noxious weeds is their aggressive, competitive behavior. Typically, they steal precious moisture, nutrients, and sunlight from the surrounding plants. Noxious weeds also alter soil properties and the composition of plant communities and change the structure of animal communities.
     Many animal species that co-evolved with native plant communities... cannot readily adapt to rapid changes in these plant communities caused by noxious weeds.
     Some wetland weeds rob waterfowl and mammals of their food sources, nesting areas, and access to water....
     Noxious weeds [can change ecological relationships].... Cheatgrass [for example] can change the frequency of fire in Sagebrush communities from approximately 50-75 years to 3-5 years. This suppresses the establishment of new Sagebrush plants and other native [plant and animal] species but provides ideal growing conditions for Cheatgrass, an annual grass.
     Some noxious weed species impact water availability and water quality. Tamarisk (Salt Cedar) now dominates plant communities in many Southwestern riparian areas. This deep-rooted tree depletes water tables and displaces native Cottonwoods and Willows which [normally would provide habitat for other native species of plants and animals]".

United States Government Definition of Noxious Weed and
Undesirable Plant Species

Definition of a Noxious Weed from the 1974 Federal Noxious Weed Act:

Noxious Weed means any living stage, such as seeds and reproductive parts, of any parasitic or other plant of a kind, which is of foreign origin, is new to or not widely prevalent in the United States, and can directly or indirectly injure crops, other useful plants, livestock, or poultry or other interests of agriculture, including irrigation, or navigation, or the fish or wildlife resources of the United States or the public health.

Definition of Undesirable Plant Species from the National Undesirable Plant Management Act of 1990:

Undesirable Plant Species means plant species that are classified as undesirable, noxious, exotic, injurious, or poisonous, pursuant to State or Federal law.

Each state in the United States has its own noxious weed laws and most undesirable plants list. Below are excerpts from Colorado's law and the entire Colorado noxious weed list,
current as of November, 2004.

From the Colorado Noxious Weed Act
Title 35 Article 5.5, enacted 1996

     The Colorado general assembly clearly recognizes the profound negative impacts of noxious weeds on the economic and environmental values of Colorado's private and public lands. Consequently, the assembly has placed all Colorado lands under the jurisdiction of local governments that have been delegated the responsibility and power to assure the management of state and locally designated noxious weeds....
     Definition of a Noxious Weed: The law defines noxious weeds as plant species that are not indigenous (non-native) to the state of Colorado and meet at least one of several criteria regarding their negative impacts upon crops, native plant communities, livestock, and the management of natural or agricultural systems. This definition applies to species listed by both the state and local governing bodies.
     Native plant species, those species that are indigenous to the state of Colorado, may not be designated as noxious weeds by either state or local governments. Furthermore, the law does not permit distinctions to be made regarding the historical range or habitats of native species. Therefore, even a native species that expands its range within Colorado due to human influences and otherwise meets the descriptive criteria as a noxious weed may not be listed as such.

The State of Colorado Noxious Weed List

The following weed species were identified by individual Colorado counties as problem weeds or were recommended for management through public testimony. Click for an updated list. Similar lists are available for Utah, Arizona, and New Mexico. The USDA Plants Database also has noxious weed lists for all states.

List A species in Colorado are designated by the Commissioner for eradication.

African rue (Peganum harmala)
Camelthorn (Alhagi pseudalhagi)
Common crupina (Crupina vulgaris)
Cypress spurge (Euphorbia cyparissias)
Dyer's woad (Isatis tinctoria)
Giant salvinia (Salvinia molesta)
Hydrilla (Hydrilla verticillata)
Meadow knapweed (Centaurea pratensis)
Mediterranean sage (Salvia aethiopis)
Medusahead (Taeniatherum caput-medusae)
Myrtle spurge (Euphorbia myrsinites)
Purple loosestrife (Lythrum salicaria)
Rush skeletonweed (Chondrilla juncea)
Sericea lespedeza (Lespedeza cuneata)
Squarrose knapweed (Centaurea virgata)
Tansy ragwort (Senecio jacobaea)
Yellow starthistle (Centaurea solstitialis)

List B noxious weed species have (or will have) a state noxious weed management plan developed to stop their spread.

Absinth wormwood (Artemisia absinthium)
Black henbane (Hyoscyamus niger)
Bouncingbet (Saponaria officinalis)
Bull thistle (Cirsium vulgare)
Canada thistle (Cirsium arvense)
Chinese clematis (Clematis orientalis)
Common tansy (Tanacetum vulgare)
Common teasel (Dipsacus fullonum)
Corn chamomile (Anthemis arvensis)
Cutleaf teasel (Dipsacus laciniatus)
Dalmatian toadflax, broad-leaved (Linaria dalmatica)
Dalmatian toadflax, narrow-leaved (Linaria genistifolia)
Dame's rocket (Hesperis matronalis)
Diffuse knapweed (Centaurea diffusa)
Eurasian watermilfoil (Myriophyllum spicatum)
Hoary cress (Cardaria draba)
Houndstongue (Cynoglossum officinale)
Leafy spurge (Euphorbia esula)

List B continued:

Mayweed chamomile (Anthemis cotula)
Moth mullein (Verbascum blattaria)
Musk thistle (Carduus nutans)
Orange hawkweed (Hieracium aurantiacum)
Oxeye daisy (Chrysanthemum leucanthemum)
Perennial pepperweed (Lepidium latifolium)
Plumeless thistle (Carduus acanthoides)
Quackgrass (Elytrigia repens)
Redstem filaree (Erodium cicutarium)
Russian knapweed (Acroptilon repens)
Russian-olive (Elaeagnus angustifolia)
Salt cedar (Tamarix chinensis, T.parviflora, and T. ramosissima)
Scentless chamomile (Matricaria perforata)
Scotch thistle (Onopordum acanthium)
Scotch thistle (Onopordum tauricum)
Spotted knapweed (Centaurea maculosa)
Spurred anoda (Anoda cristata)
Sulfur cinquefoil (Potentilla recta)
Venice mallow (Hibiscus trionum)
Wild caraway (Carum carvi)
Yellow nutsedge (Cyperus esculentus)
Yellow toadflax (Linaria vulgaris)

List C noxious weed species: Resources will be provided to jurisdictions that choose to require management of these species.

Chicory (Cichorium intybus)
Common burdock (Arctium minus)
Common mullein (Verbascum thapsus)
Common St. Johnswort (Hypericum perforatum)
Downy brome (Bromus tectorum)
Field bindweed (Convolvulus arvensis)
Halogeton (Halogeton glomeratus)
Johnsongrass (Sorghum halepense)
Jointed goatgrass (Aegilops cylindrica)
Perennial sowthistle (Sonchus arvensis)
Poison hemlock (Conium maculatum)
Puncturevine (Tribulus terrestris)
Velvetleaf (Abutilon theophrasti)
Wild proso millet (Panicum miliaceum)

Asteraceae (Sunflower Family)	Asteraceae (Sunflower) Family	Asteraceae (Sunflower) Family	Asteraceae (Sunflower) Family

*Carduus nutans*	Centaurea diffusa	Cichorium intybus	*Leucanthemum vulgare*
Musk Thistle	Knapweed	Chicory	Ox-eye Daisy
CO, NM, UT	CO, NM, AZ, UT	CO	CO

Boraginaceae (Forget-Me-Not Family)	Brassicaceae (Mustard Family)	Brassicaceae (Mustard Family)

*Cynoglossum officinale*	Capsella bursa-pastoris	*Descurainia sophia*
Hound's Tongue	Shepherd's Purse	Tansy Mustard
CO

Convolvulaceae (Morning Glory Family)	Elaeagnaceae (Oleaster) Family	Geraniaceae (Geranium Family)

*Convolvulus arvensis*	Elaeagnus angustifolia	*Erodium cicutarium*
Bindweed	Russian Olive	Filaree
AZ, CO, NM, UT	CO, NM, UT	CO

Scrophulariaceae (Snapdragon Family)	Scrophulariaceae (Snapdragon Family)	Scrophulariaceae (Snapdragon Family)	Tamaricaceae (Tamarisk) Family	Ulmaceae (Elm Family)

*Linaria dalmatica*	*Linaria vulgaris*	*Verbascum thapsus*	*Tamarix chilensis*	*Ulmus pumila*
Butter and Eggs	Butter and Eggs	Mullein	Tamarisk	Siberian Elm
CO, NM	CO, NM	CO	CO, NM	NM