Noxious Weeds are non-native plants that have become established or that may be introduced in the state.  These Noxious Weeds may render land unfit for agriculture, forestry, livestock, wildlife, or other beneficial uses.  These plants are designated as “Noxious” by rule of the Montana Department of Agriculture or as a District Noxious Weed by the Yellowstone County Weed Board.

Weed Management Criteria – The following criteria apply to management of noxious weeds in Yellowstone County.  Noxious Weeds in Yellowstone County are those declared “noxious” by the Weed Board and are prioritized accordingly.  These weeds will be managed to achieve two effects:  1.)  limit and prevent the spread of noxious weeds from existing infestations to uninfested sites and 2.)  to eventually reduce the overall size of the existing infestations.  The following weeds exist in the county and have been declared “noxious” in Yellowstone County by the Yellowstone County Weed Board.

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Priority 1A: These weeds are not present in Montana. Management criteria will require eradication if detected; education; and prevention.

Yellow Starthistle (Centaurea solstitialis)

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Priority 1B: These weeds have limited presence in Montana. Management criteria will require eradication or containment and education.

Dyers Woad (Isatis tinctoria)
Flowering Rush (Butomus umbellatus)
Japanese knotweed complex (Polygonum spp.)
Purple Loosestrife (Lythrum spp.)
Rush Skeletonweed (Chondrilla juncea)
Eurasian Watermilfoil (Myriophyllum spicatum)
Scotch Broom (Cytisus scoparius)
Curlyleaf pondweed (Potamogeton crispus) - Montana Weed Control Association

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Priority 2A: These weeds are common in isolated areas of Montana. Management criteria will require eradication or containment where less abundant. Management shall be prioritized by local weed districts.

Tansy Ragwort (Senecio jacobea L.) 
Meadow Hawkweed Complex (Hieracium pratense, H. floribundum, H. piloselloides)
Orange Hawkweed (Hieracium aurantiacum L.)
Tall Buttercup (Ranunculus acris L.)
Perennial Pepperweed (Lepidium latifolium)
Yellow Flag Iris (Iris pseudacorus)
Blueweed (Echium vulgare)
Hoary Alyssum (Berteroa incana)

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Priority 2B: These weeds are abundant in Montana and widespread in many counties. Management criteria will require eradication or containment where less abundant. Management shall be prioritized by local weed districts.

Canada Thistle (Cirsium arvense)  
Field Bindweed (Convolvulus arvensis)
Leafy Spurge (Euphorbia esula)
Whitetop (Cardaria draba) 
Russian Knapweed (Centaurea repens)
Spotted Knapweed (Centaurea maculosa)
Diffuse Knapweed (Centaurea diffusa) 
Dalmation Toadflax (Linaria dalmatica) 
St. Johnswort (Hypericum perforatum)
Sulfur Cinquefoil (Potentilla recta)
Common Tansy (Tanacetum vulgare L.) 
Oxeye Daisy (Chrysanthemum leucanthemum L.)
Houndstongue (Cynoglossum officinale L.)
Yellow Toadflax (Linaira vularis)
Saltceder (Tamarix spp.)

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Priority 3: Regulated Plants: (Not Montana Listed Noxious Weeds)
These regulated plants have the potential to have significant negative impacts. The plant may not be intentionally spread or sold other than as a contaminant in agricultural products. The state recommends research, education and prevention to minimize the spread of the regulated plant.

Cheatgrass (Bromus tectorum) - Montana Weed Control Association
Hydrilla (Hydrilla verticillata) - Montana Weed Control Association

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County Designated

Poison Hemlock (Conium maculatum L.) 
Western Water Hemlock (Cicuta douglasii)
Puncturevine (Tribulus terrestris L.)  
Common Teasel (Dipsacus fullonum L.)
Common Mullein (Verbascum thapsus L.)

In addition to the Montana State Listed Noxious Weeds, each county weed district can declare additional non-native plants to be noxious within the county. Yellowstone County declares the above weeds noxious.