Vital Ground Fights Noxious Weeds with Bugs

Close-up photo of weevil on tree bark
Photo: iStock
Weevils that feed on noxious weeds can be valuable bio-controls and restoration agents for an ecosystem. Thanks to a grant from the Montana Department of Natural Resources and the U.S. Forest Service, Vital Ground is employing 1,500 root-boring weevils to control the spread of invasive knapweed at Alvord Lake Community Forest.

By Mitch Doherty

The Alvord Lake Community Forest is a long way from the warm, exotic climate found in the Mediterranean, but the 1,500 migrant knapweed root-boring weevils native to another continent should find the new setting delightful and the forage abundant.

In 2017, through a grant funded by the Montana Department of Natural Resources and the U.S. Forest Service, the dark gray-and-white speckled bio-control agents known as knapweed root-boring weevils were released at Vital Ground’s Alvord Lake Community Forest near Troy, Montana.

Like many areas throughout the northern Rockies, the Alvord Lake Community Forest, which was once managed as corporate timber grounds, suffers from invasion of the non-native plant spotted knapweed. The comprehensive Alvord Lake Community Forest Management Plan, drafted by local volunteers and a host of partners, calls for an integrated approach to weed management on the forest that includes the use of both herbicide and bio-controls such as root-boring weevil.

In the coming years these industrious bugs will help reduce purple-flowered noxious weeds by laying up to 100 eggs each in deposits on the root crown of the plant. Once the larva emerges, it feasts on the plant’s root tissue, subsequently stunting the flow of nutrients and destroying the plant after one year.

Adult weevils will feed on green, tender leaves, but the most damage is caused by larva. These hardy bugs are able to winter in climates found in the northern Rockies and will emerge in the spring to resume gnawing roots, thus making them a long-term solution to manage knapweed on the forest.

This year Vital Ground submitted an application for additional funding to continue weed-control activities such as root-boring weevil. The request also included a myriad of other proposed forest-stewardship activities all aimed at supporting the long-term recovery of this former piece of corporate timberland to promote a healthy forest, improve wildlife habitat, and to enhance the experience for outdoor enthusiasts who recreate at Alvord Lake.

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