skip to Main Content

Noxious Weeds

Noxious weeds are a problem that gets progressively worse the longer treatment is delayed. Dealing with noxious weeds quickly and effectively is necessary to maintain the environmental, economic, and recreational value of your land.

  1. What are noxious weeds?



Noxious weeds are invasive plants that the State of Montana has declared a nuisance and are harmful to the native environment, croplands, and livestock. Noxious weeds were intentionally or accidentally introduced from Europe and Asia, and do not have naturally occurring controlling agents here (predation, disease) which allows them to flourish.






Over the past century noxious weeds have infested about 9% of Montana’s land area causing economic and ecological harm. It is estimated that leafy spurge and spotted knapweed have caused biomass production of Montana ranches to fall by 0.7 to 0.8%. Weeds disrupt native ecosystems and displace native plants, causing widespread impacts that affect wildlife, water quality, and scenic values.


  1. What are some noxious weeds in Montana?

Noxious weeds of Montana, pictures, identification tools, and treatment techniques are listed at Some of the most important noxious weeds in Montana are:

  1. Spotted knapweed
  2. Canada thistle
  3. Leafy spurge
  4. Russian olive
  5. Salt cedar
  6. Cheatgrass
  7. Eurasian watermilfoil
  8. Dalmation toadflax
  1. Treatment

In Montana you are required by law to manage noxious weeds on your property. “It is unlawful for any person to permit any noxious weed to propagate or go to seed on the person’s land, except that any person who adheres to the noxious weed management program of the person’s weed management district or who has entered into and is in compliance with a noxious weed management agreement is considered to be in compliance with this section.” (Title 7, Chapter 22, Part 21)

You will need to develop a weed management plan with your county weed district and gain approval by your local weed board.

Application of certain pesticides requires applicator training through MSU Extension.

An important concept to know is that of a seedbank. Live seeds can be present on land even when the mature plant is not and can remain viable for years. Learn more about the seedbank characteristics and management through this University of Nevada resource.


  1. Resources

The Montana Weed Control Association has a wealth of resources on weed identification, treatment, and planning.

Back To Top