Noxious weed is a legal definition associated with an invasive plant that has been introduced into an environment and causes or is likely to cause environmental or economic harm.
Many noxious weeds are pretty, but their effects are not. Pathogens, microbial activity in the soil, and absence of natural enemies in their new environment can allow noxious weeds to spread like a wildfire, transforming ecosystem function including biotic and abiotic processes.
In Wyoming, there are two “noxious weed lists” that a species can be placed on. One is the State Designated list where the species has been determined to be detrimental statewide. The other is the County Declared list where a local Weed and Pest District has determined the species to be a concern within that county. The legal definitions as per the Wyoming Weed & Pest Control Act are as follows:
“Designated noxious weeds” means plant species having seeds or other plant parts determined to be detrimental to the general health or welfare of the state based upon the following:
(A) Has demonstrated the ability to aggressively invade native plant communities and agricultural crops;
(B) Is injurious or poisonous to livestock;
(C) Is a carrier of disease or parasites;
(D) Can, by virtue of either direct or indirect effect, negatively impact management of agricultural or natural ecosystems.
“Declared weed” means any plant species which the district Weed & Pest board and the Wyoming weed and pest council have found, either by virtue of its direct or indirect effect to negatively impact management of agricultural or natural ecosystems, or as a carrier of disease or parasites, to be detrimental to the general welfare of persons residing within a district.
The Wyoming Weed & Pest Control Act can be found here under Title 11, Chapter 5