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Taking on weeds

Noxious weeds crowd out

many native plants, including palatable forage for livestock and wildlife. The Nature Conservancy is committed to working with landowners across Montana to address this growing threat. 

In the Centennial Valley, Conservancy interns began setting up weed control projects with ranchers and other agencies in 1998. Since then, they have helped organize the largest weed district in the state, in Beaverhead County.

Now student interns have broadened their efforts to include the Big Hole and Madison Valleys.

Along the Rocky Mountain Front, Conservancy staff are working with the Rocky Mountain Front Weed Roundtable to combat invasive species. The effort has grown to involve more than 230 landowners, agencies, volunteers and Montana Conservation Corps in fighting weeds in seven of the Front's main watersheds. The effort includes mapping and monitoring noxious weeds, pulling and spraying them, using biological control insects and managing desirable plant communities. 

The Conservancy and its partners created a Front-wide weed map, which will help managers monitor weeds and apply effective control strategies.

In southern Phillips County, north of the Missouri Breaks, ranchers participating in the Matador Ranch Grassbank have committed to strict weed control. The goal is a 1 million-acre noxious weed free zone in southern Phillips County.

The Conservancy is also assisting ranchers and agency partners in the Blackfoot and Yellowstone Valleys,

The Conservancy also works to control noxious weeds at some of its preserves. At Dancing Prairie in northwestern Montana, the most invastive noxious weeds are spotted knapweed, sulfur cinquefoil, leafy spurge and St. John's work. The Conservancy's stewardship staff annually inventory and treat these species.

 
Identifying weeds
Conservancy intern IDs a weed.
© Jim Steinberg

Weed Facts

  • Noxious weeds are the number two cause of wildlife habitat loss in Montana. 
  • In Montana, noxious weeds infest about 8 million acres, or roughly 9 percent of the state.
  • Spotted Knapweed and Leafy Spurge are among the most widespread, each infesting more than 1 million acres in the western United States.

Weed Management Strategies

Conservancy staff have studied the benefits of various weed management strategies in three Montana landscapes: the Rocky Mountain Front, the Centennial Valley and Montana's Northern Prairie. Some key findings:

  • Early detection and control has the greatest value and lowest long-term cost than large patch control strategies.
  • On the Front, early detection and control was most effective when combined with efforts to control the edges of large existing weed patches.
  • Allocating a larger treatment budget in the short term can have a great benefit in terms of the ultimate outcome in the area invaded. In the Centennial Valley, for example, doubling the annual budget resulted in a tenfold decrease in the area invaded by Spotted Knapweed after 50 years.