Noxious weeds primarily consist of plants that are not native to the North American continent. They are plants that have the ability to adapt to a wide variety of soil and climatic conditions, but have no natural enemies. They compete well for soil moisture, nutrients, and sunlight. As a result, weeds can out-compete everything from native grasses to agricultural crops.
Weed species growing in the Refuge and throughout the Bitterroot Valley include: Spotted Knapweed (Centaurea maculosa), Musk Thistle (Carduus nutans), Canada Thistle (Cirsium arvense), Bull Thistle (Cirsium vulgare), Leafy Spurge (Euphorbia esula), St. Johnswort (Hypericum perforatum), Burdock (Arctium minus) and Hound's Tongue (Cynoglossum officinale L.).
The Refuge implements an integrated pest management program designed specifically for research and control of noxious weeds. This program combines various management tools to control the spread of non-native weed species including: biological control agents, prescribed fire, and herbicides.