Insights on Sixteen Years of Invasive Plant Management in the Bear Trap Canyon Wilderness

By Celestine Duncan Photographs by Celestine Duncan unless otherwise noted.

By Celestine Duncan

Photographs by Celestine Duncan unless otherwise noted.

Figure 1. The Madison River flows through lower Bear Trap Canyon.

Flowing north from its headwaters in Yellowstone National Park, the Madison River rushes through a nine-mile scenic gorge in the Bear Trap Canyon Wilderness before joining the Gallatin and Jefferson Rivers at Three Forks, Montana (Figure 1). The 6,347-acre wilderness area managed by the Bureau of Land Management (BLM) is noted for premier Class IV and V whitewater rafting, towering scenic cliffs, and excellent fly fishing, hiking, and camping opportunities.

Figure 2. Disturbance caused by periodic burns favors invasion of non-native plants such as spotted knapweed

Figure 2. Disturbance caused by periodic burns favors invasion of non-native plants such as spotted knapweed

Mike Mooney, Range Technician and Invasive Plant Program Manager with the Dillion BLM office, is tasked with managing noxious weeds in the Bear Trap Canyon Wilderness. “It’s always a challenge managing invasive plants where access is difficult, and this is no exception,” explains Mooney. “It’s a beautiful area with great water-based recreation, so it receives a lot of public use, mainly concentrated along the river corridor.”

Figure 3. Mike Mooney, BLM, organizes crews for the annual spray day

Noxious weeds were introduced and established in the canyon more than 40 years ago and thrived because of disturbance from recreational activities, floods, and wildfires (Figure 2). In April 2001 employees with the BLM, Madison and Gallatin County Weed Districts, U.S. Forest Service, Greater Yellowstone Coalition, Montana Wilderness Society, and other interested individuals floated through the Bear Trap Wilderness. This group determined that the size, density, and location of spotted knapweed (Centaurea stoebe) and leafy spurge (Euphorbia esula) infestations precluded eradication; however, they developed a long-term control and containment strategy that remains in effect today.

Figure 4. Volunteers and weed crew members hike into Bear Trap Wilderness during the annual spray day.

Figure 4. Volunteers and weed crew members hike into Bear Trap Wilderness during the annual spray day.

“We agreed on an integrated approach that includes the release of biological control agents on large infestations of leafy spurge and spotted knapweed, and on infested sites that are difficult to access, while selective herbicides are applied to more accessible infestations and along trails and other high-use areas with disturbance,” explains Mooney. The BLM also improved trails within the wilderness and upgraded roads, parking, and camping areas adjacent to wilderness boundaries, reducing disturbance caused by recreational activities. BLM employees are on site during peak-use months to minimize off-site driving, parking, and camping.

Figure 5. Erik Broeder and Karen Ward, BLM, mix herbicide onsite for weed treatments.

Figure 5. Erik Broeder and Karen Ward, BLM, mix herbicide onsite for weed treatments.

The partnerships have remained strong during the 16-year commitment. Hike-in spray days are conducted twice each year and include volunteers and crews from county weed districts, the Butte and Dillon BLM offices, Montana Youth Challenge Academy, Montana Conservation Corps, private landowners, and others. In addition, the BLM hosts a minimum of two floats per year to treat noxious weeds along the river and associated uplands that are accessible only by rafts. Herbicides are packed in dry boxes and mixed on site to minimize the potential for water contamination.

Figure 6. Jacob Huffied and Chase Grover, Madison County Weed District, pause on the trail prior to treating weeds.

Figure 6. Jacob Huffied and Chase Grover, Madison County Weed District, pause on the trail prior to treating weeds.

Karen Ward, Engineering Technician for the BLM Dillon Field Office, was part of the volunteer spray crew in May 2017. “It’s such a great team-building exercise,” Ward says. “The spray day gives us a chance to get out of the office and work with crews to understand what they do and why invasive weeds are such a problem.” Jacob Huffied and Chase Grover with Madison County Weed District agree and explain that it’s a great chance to meet and work with other county and federal partners on a worthwhile project (Figures 3 through 6).

Figure 7. Spotted knapweed flourished along the wilderness trail in 2001 (top) compared to the same trail today, showing native grass response following a reduction in spotted knapweed (bottom).

Figure 7. Spotted knapweed flourished along the wilderness trail in 2001 (top) compared to the same trail today, showing native grass response following a reduction in spotted knapweed (bottom).

During the past 16 years, the number of volunteers has varied between 20 and 55 with a core group of permanent and seasonal BLM Dillon Field Office and Madison County Weed District staff who work each year. The Montana Youth Challenge Academy has provided from four to six cadets each year since 2010, and Beaverhead and Gallatin County Weed Districts have partnered following wildfire events. In addition, a Montana Conservation Corps crew has been hired the past three years to treat infestations on sites that are more difficult to access or are missed during the volunteer work days.

Program Effectiveness

Herbicide treatments include Tordon® 22K specialty herbicide, applied either alone or in combination with 2,4-D on leafy spurge and spotted knapweed on upland sites. Infestations located within 30 feet of the river are treated with 2,4-D alone. Biological control agents on spotted knapweed and leafy spurge have spread throughout the project area over the past 16 years. Although agents are well established, populations haven’t increased to levels needed for effective control at most locations. Augmenting biological control insect populations, especially following wildfire events, appears to be important to increase their impact on target weeds.

For more information on Opensight® go to bit.ly/2rBZ4rt.

Some challenges remain in the project area. Hoary alyssum (Berteroa incana), an invasive mustard (Box 1), has increased in dominance on some sites as spotted knapweed and leafy spurge declined. “We need to shift our herbicide treatments to include products that are effective on both mustard species and knapweed,” says Mooney. Establishing effective control of leafy spurge, knapweed, and downy brome (Bromus tectorum) on canyon walls also continues to be a challenge.

Mike Mooney is proud of the results they have seen over the last 16 years. “After the first year of treatment, we were surprised at how the native grasses came back and competed with spotted knapweed (Figure 7). Throughout the project area, weed infestation levels have decreased with a few spikes during years with more precipitation” Mooney explains.

Controlling noxious weeds in the Bear Trap Wilderness has shown that even if you have large infestations that are hard to access, control can be achieved with help from others and persistence. Even though the number of volunteers over the years has gradually increased, the amount of herbicide applied has significantly decreased. The use of BLM staff helps to educate everyone on the impacts of noxious weeds and the methods of control. It has also given the people who have taken part over the years a sense of accomplishment by being able to see that their efforts have made a difference.

For more information about this project, or to volunteer for future spray days, contact the BLM Dillon Field Office at (406) 683-8000.


®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

Milestone and Opensight are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.

Milestone and Opensight: When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details.

State restrictions on the sale and use of Milestone and Opensight apply.  Consult the label before purchase or use for full details.  Always read and follow label directions.

Tordon 22K is a federally Restricted Use Pesticide.

Active ingredients for herbicide products mentioned in this article.  Product (active ingredient): Tordon 22K (picloram); 2,4-D; Milestone (aminopyralid); Opensight (aminopyralid and metsulfuron-methyl).