Montana Noxious Weeds

7.6 Million Acres in Montana are infested with Noxious Weeds. There are 33 plants listed as Noxious Weeds in Montana, and 5 listed as Regulated Plant species.

About 70% of Montana is considered range land.

Land owners have a legal responsibility to manage state listed noxious weeds as well as any county listed noxious weeds for the county in which the property is located.

A Weed is a plant growing where it isn’t wanted. A Noxious Weed is a plant growing where it isn’t wanted and has the capability and capacity to be injurious to livestock, agriculture and the environment.

A noxious weed has a competitive advantage over most native plants through its numerous biological traits(e.g. seed appendages for transport, extensive root system, fast growth rate). These traits allow noxious weeds to establish and spread to new habitats, seemingly without further assistance from humans.


  • Displace native plants
  • Reduce crop yield and livestock forage
  • Diminishes quality of wildlife habitat
  • Decreases property value

Control Costs

  • Herbicide costs range from $5 – $35 per acre
  • Long-term investment of time & money

Weed Lifecycles & Persistence

Annual – example: Yellow Starthistle

Biennial – example: Houndstongue

Perennial – example: Spotted Knapweed

Grass vs. Forb

For the management of weeds it is important to know the difference between Grass and Forbs because some herbicides will only work on one, and not the other.


  • Flowers-not showy, usually the same color as the leaves and stems
  • Leaf veins run parallel
  • Stems-jointed and hollow
  • Roots – fibrous


  • Flowers – showy & colorful
  • Leaves – net like veins
  • Stems – solid
  • Roots – bulb, taproot or fibrous


The majority of Montana’s noxious weeds are perennials that have a taproot.

Montana State Listed Noxious Weed Species

The most widespread noxious weeds in Montana are Canada thistle, spotted knapweed and leafy spurge. Other weeds abundant in Montana and widespread in many counties include: • Common tansy • Dalmatian toadflax • Diffuse knapweed • Field bindweed • Houndstongue • Oxeye daisy • Russian knapweed • Saltcedar • St. Johnswort • Sulfur cinquefoil • Whitetop • Yellow toadflax

Priority 1A

These weeds are not present or have a very limited presence in Montana. Management criteria will require eradication if detected, education and prevention.

  • Yellow Starthistle*
  • Dyer’s Woad
  • Phragmites

Priority 1B

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

  • Knotweed Complex
  • Purple Loosestrife
  • Rush Skeletonweed
  • Scotch Broom

*Yellow Starthistle does not currently occur in Montana, but is found in Idaho, Washington, and California.

Priority 2A

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

  • Flowering Rush
  • Eurasian Watermilfoil
  • Tansy Ragwort
  • Meadow Hawkweed Complex
  • Orange Hawkweed
  • Tall Buttercup
  • Perennial Pepperweed
  • Yellowflag Iris
  • Blueweed

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.

  • Hoary Alyssum
  • Canada Thistle
  • Field Bindweed (Morning Glory)
  • Leafy Spurge
  • Whitetop
  • Russian Knapweed
  • Spotted Knapweed
  • Diffuse Knapweed
  • Dalmation Toadflax
  • St. Johnswort
  • Sulfur Cinquefoil
  • Common Tansy
  • Oxeye Daisy
  • Houndstongue
  • Yellow Toadflax
  • Salt Cedar
  • Curlyleaf Pondweed

Priority 3 Regulated Plants

(Not Montana Listed Noxious Weeds)

These regulated plants have the potential to have significant negative impact. 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.

  • Russian Olive
  • Cheatgrass
  • Hydrilla
  • Brazillian Waterweed
  • Parrotfeather

Montana County Noxious Weed Control Act

Montana developed its first noxious weed law in 1985. Species listed were Canada Thistle, Scotchbull Thistle, and Russian Thistle.

1948 Montana Legislature Passes the Montana County Noxious Weed Control Act. Defines the term “noxious weed” as any exotic plant species which may render land unfit for agriculture, forestry, livestock, wildlife or other beneficial uses or that may harm native plant communities.

Benefits of Managing Noxious Weeds

  • Enhance property value
  • Improve aesthetics
  • Save money and time and reduce longer-term maintenance costs
  • Improve wildlife habitats
  • Improve forage for horses and other livestock
  • Protect water resources
  • Protect Native plants
  • Be a good neighbor

Integrated Weed Management

Integrated Weed Management is the combination of multiple management tools to reduce a weed population to an acceptable level. Eradication may or may not be possible depending on the degree of infestation.

4 Golden Rules

  1. Know what you want to do with your propertyLandowners may need to change the way things are done or change what they want to do with the land.
  2. Promote healthy vegetationHealthy, desirable plants use available plant resources(water, nutrients, sunlight) and keep them from being used by weeds
  3. Implement good land use practicesOvergrazing or excessive soil disturbance related to construction are invitations to weeds
  4. No one weed control method works aloneStrategically combining control methods will lead to success

Integrated Weed Management attempts to stop weeds, especially noxious or injurious weeds, from competing with domesticated plants and livestock. Many strategies have been developed in order to contain these plants.

Prevention: any action that stops weeds from establishing

Mechanical: physical activities that destroys or inhibits weed growth

  • Hand pulling
  • Mowing/cutting/clipping

Chemical: application of chemical that is toxic to plants

  • Herbicide

Biological: use of natural enemies to limit weed growth and reproduction

  • Insects
  • Grazing: cattle, sheep, goats
  • Burning/Fire

Cultural Controls: any technique that involves maintaining field conditions so that weeds are less likely to grow

  • Re-seeding, irrigation, cultivation, fertilization, proper grazing, maintaining competitive vegetation

Montana Noxious Weed Resources




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