Noxious Weeds

What exactly is a weed?

A weed is defined as, “a plant that is not valued where it is growing and is usually of vigorous growth, especially: one that tends to overgrow or choke out more desirable plants” (Merriam-Webster).

What makes a weed ‘noxious’?

A noxious weed is defined by Montana Law (MCA 7-22-2101) as, “any exotic plant species established or that may be introduced in the state that may render land unfit for agriculture, forestry, livestock, wildlife, or other beneficial uses or that may harm native plant communities.”  A noxious weed is any unwanted non-native plant with potential impact serious to the extent that it has been declared by the state of Montana that landowners must enter into an approved management program to keep it from spreading.

Did you know Montana's state listed noxious weed species?

A weed gains ‘noxious’ status through rule making authority by the Montana Department of Agriculture, as a district noxious weed by a county weed board and/or following public notice of intent and a public hearing regarding the status of a weed. If a weed is designated as a statewide noxious weed by rule of the Department of Agriculture, that weed must be considered noxious in every county of the state. 

How are noxious weeds classified in Montana?

State designated noxious weeds are categorized into five different levels or Priorities. These levels are classified as priorities 1A, 1B, 2A, 2B and 3.  This ranking system is based on the management techniques used to control the species as well as their presence and population density.  In Montana, there is only one species of noxious weed listed under Priority 1A, and currently this plant, Yellowstar thistle is not present in the state.  Under each Priority listing there is a brief description of what is to be done if the species listed under that Priority is found.  Also listed under each Priority heading are the species inlcuding their scientific name.  Montana is a large state.  In addition to state-listed noxious weeds, it is a good idea to learn about what noxious weeds are listed in your county, how to identify these species, and what actions you can take to stop their spread.

Noxious Weed Identification

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Do Your Part

Over the past 150 years, both the rate of introduction and spread of noxious weeds have increased significantly. This change is due to an increase in human travel, expanding commerce through trade, and a lack of knowledge of how weeds are spread. By becoming educated about noxious weeds, you’re doing your part to help stop their spread and protect the environment.

If noxious weeds are left uncontrolled, the Montana that we enjoy today will look much different for future generations. Do your part, become educated and help stop the spread of noxious weeds.


§7-22-2101, MCA. County Weed Act. 16 Nov. 2012. Retrieved from:

“weed”. Merriam-Webster, 2011. Web. 16 Nov. 2012.

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County Weed Act

Montana Noxious Weed List (2013)