Watch Out For These Weeds!

photo of a pile of black bags loaded with weeds
Removing weeds from the range, one bag at a time.


The Grand Mesa, Uncompahgre, and Gunnison (GMUG) National Forests are spectacular areas that are home to a variety of plants and animals. Unfortunately, certain plants have been introduced to the environment that do not belong here. These plants may have escaped from gardens or arrived as hitchhikers on clothes, fur, or vehicles. There a number of these invaders in the GMUG and they are considered 'weeds' (plants out of place). Some of these are designated by law as 'noxious weeds' if the plant or plant product can cause great ecological and/or environmental harm (Plant Protection Act of 2000).


When an invasive weed species is introduced to an area where it does not usually grow, it 'grows like a weed' due to the lack of natural enemies to keep its population size in check. Weeds can affect the health and sustainability of ecosystems in the GMUG and may be deadly to livestock or wildlife if ingested. These plants grow fast and compete for resources with native plant species. Once established, it can be costly and time-consuming to remove these invaders. Weeds may be controlled via chemical or non-chemical means to inhibit their spread and the GMUG uses both options on our forests.


The weeds shown below are some of the top concerns within the GMUG. If you see any of these weeds, please let us know! The best way is to take a GPS point of the location and take photographs of the weeds. Photographs of the area where you located the weeds as well as close up photographs of the flower, stem, and leaves will aid with identification.



Russian knapweed (Acroptilon repens) and spotted knapweed (Centaurea maculosa) are a concern in our forests. Both of these weeds are native to Europe. Russian knapweed is known to be toxic to horses. 

weed with yellow and pink flowers weed with pink flowers
Russian knapweed
Spotted knapweed



Thistle are difficult to identify since there are native forms of this plant in Colorado that look very similar to the non-native weeds. Species that are considered weeds are the Canada thistle (Cirsium arvense), bull thistle (Cirsium vulgare), musk thistle (Carduus nutans), and Scotch thistle (Onopordum acanthium) to name a few. These thistle are native to Europe and Asia.

weed with spiky leaf
tall weed with pink flowers
Bull thistle leaf
Musk thistle



Yellow toadflax (Linaria vulgaris) and Dalmatian toadflax (Linaria dalmatica) are native to Europe and Asia. Both species of toadflax are an escaped ornamental plant, meaning it was originally grown for its beauty in people's gardens. These species have been known to hybridize, therefore a plant may have characteristics of both species.

weed with yellow flowers green weedy leaf, spiral
Dalmation toadflax
Leaves of the Dalmation toadflax


Oxeye Daisy (Leucanthemum vulgare)

This weed is an escaped ornamental plant and it is native to Europe and Asia. Oxeye daisies can produce over 200 seeds per flower head.

weed with white flowers weed with white flowers
Oxeye daisies up close- photo from CO Dept of Agriculture
Field of oxeye daisies- photo from CO Dept of Agriculture


Hoary Cress (Cardaria draba)

Hoary cress is native to Europe and Asia. It is also called 'Whitetop' due to the small white flowers it produces.

weed with white flowers
Hoary cress- photo from CO Dept of Agriculture


Hounds-tongue (Cynoglossum officinale)

This weed has a variety of names– beggar’s lice, dog’s tongue, sheep bur, dog bur, sheep lice, gloverwort and woolmat. It has seeds with that stick to everything from fur to clothing. This weed is native to Europe and Asia. It can be toxic to livestock, especially horses.

photo of weeh flower
Hounds-tongue can be toxic to livestock.


Cheatgrass (Bromus tectorum)

This is a grass typically found in Europe and parts of Asia and Africa but has been introduced to North America. It can increase the spread of wildfire due to its flammability and has been known to overtake any area it grows in.

tall grass, invasive


Below is an extensive list of all noxious weeds found on the GMUG.


List of Noxious Weeds Found on the GMUG


Scientific Name Common Name
Priority 1 Species
Cirsium arvense Canada thistle
Linaria vulgaris butter and eggs or yellow toadflax
Potentilla recta sulphur cinquefoil
Carduus nutans musk thistle
Anthemis arvensis corn chamomile
Leucanthemum volgare oxeye daisy
Cynoglossum offinale hounds-tongue
Cardaria draba whitetop/hoary cress
Centaurea stoebe spotted knapweed
Cirsium volgare bull thistle
Acroptilon repens Russian knapweed
Priority 2 Species
Verascum thapsus common mullein
Hyoscyamus niger black henbane
Convolvulus arvensis field bindweed
Tripleurospermum perforatum scentless chamomile
Arctium minus lesser/common burdock
Artemisia absinthium Absinthe wormwood
Centaurea diffusa diffuse knapweed
Carduss acanthoides spiny plumeless thistle
Salsola tragus prickly Russian thistle
Cichorium intybus chicory
Priority 3 Species
Bromus tectorum cheatgrass
Onopordum acanthium Scotch thistle
Tanacetum volgare common tansy
Linaria dalmatica Dalmation toadflax
Tamarix ramosissima saltcedar
Lepidium latifolium broadleaved pepperweed
Elaeagnus angustifolia Russian olive
Euphorbia esula var. uralensis Russian leafy spurge
Priority 4 Species
Anthemis cotula mayweed chamomile
Carum carvi caraway
Senecio jacobaea stinking willie/ tansy ragwort
Dipsacus fullonum Fuller's teasel


For more information on weeds please use the following links:

Noxious Weed List for the state of Colorado

USDA Plants Database with information on federal and state noxious weeds as well as native plants

US Forest Service Weed Research Information