Bugs Fight Invasive Knapweed at Wild River

Root weevils at Vital Ground's Wild River Project
Photo: Kali Becher
Root weevils are helping control the spread of invasive knapweed as part of the habitat restoration process at Vital Ground's Wild River Project in northwestern Montana.

By Kali Becher, Land Steward

Once Vital Ground purchases a piece of habitat or closes on a conservation easement with a landowner, the work is really just beginning. Protected habitat is only valuable to wildlife if it helps meet their needs of food, shelter and space. That often means restoration projects are the next step in our efforts to conserve and steward vital habitat for grizzly bears and other wildlife.

Invasive plants can do a number on the biodiversity and habitat value of an area, which is why Vital Ground is committed to controlling noxious weeds and restoring native plant communities on the properties we manage. One site where we are working on this is our Wild River Project along Montana’s Kootenai River, a key linkage area where restored habitat will help wildlife cross safely between the Cabinet and Purcell mountains.

In August, we released a biocontrol called Cyphocleonus achates at Wild River. This insect is a root weevil that attacks spotted knapweed plants by tunneling and laying eggs in the plant’s roots. Another biocontrol that attacks spotted knapweed by feeding on its leaves and seeds, Larinus spp., is widespread in western Montana and was already present at the property. The use of these two biocontrols together can kill small knapweed plants, and overall will reduce the density of the knapweed infestation and reduce plant vigor. Biocontrols are the natural enemies of invasive species and are employed to help control these species outside of their native range, but only after extensive experiments and trials to ensure that the insects only target noxious weeds and do not harm other beneficial plants. As a result, biocontrols are a cost-effective method for controlling invasive species.

Combine the effects of biocontrols with selective herbicides targeting invasive species and hand-pulling of noxious weeds, and you can really start to see dramatic improvements. This multi-pronged approach is called integrated invasive species management, and it is what we are doing at Wild River. While we released biocontrols focused on knapweed, our invasive species management work at the property has targeted all the listed noxious weeds present. Decreasing the amount of noxious weeds is just the first step to restoring the native plant community at Wild River and therefore improving its habitat value. The next step will be to re-establish native plants through planting and spreading native plant seeds, which will happen in 2020, in addition to continuing to control the invasive species using an integrated approach.

Big thanks to our partners on this habitat restoration project! They include: Patagonia, the Montana Biological Weed Control Coordination Project, the Missoula County Weed District and Extension and its Youth in Restoration Crew.

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