A root weevil, above, raised and harvested by Gus Vaile, takes its place on the flower of the invasive Knapweed. Below, Vaile shows how the seed weevil, which he also raised and harvested, settles into his new home on this Knapweed plant.

There are any number of things that can cause trouble for a farmer and their crop or herd. An overly dry season, an overabundance of rain, wildfires, wildlife and especially an invasive species of weeds. In northern Montana, the aggressive Knapweed has been an unwanted tenant in many farmers and ranchers’ fields since it was accidentally introduced from Central Europe over a century ago. 

Spotted Knapweed, or Centaurea stoebe, is very hostile when it makes its way into a field and quickly dominates the previous resident of that area. It causes a host of problems for farmers including soil erosion, the cost of removal, reduced plant diversity and an increased cost of general production. 

The fight against this invasive species is often taken with a chemical spray approach. However, Gus Vaile and Lester Gray in Babb, Mont., have taken on a more natural method to weeding out the Knapweed. Their approach comes in the form of insects, raised specifically at his bug insectary in Babb for the destruction of various Knapweed species. 

The duo works through a Conservation Stewardship Program of the Natural Resource Conservation Service and has been part of the Farm Service Agency for nine years. 

Despite Vaile’s early speculation about the effectiveness of insects to treat Knapweed, he changed his mind after seeing the results. 

“A lot of people are skeptical at first when it comes to combating Knapweed this way,” Vaile said. “However, there are a lot of benefits to using this method and it makes a big difference for farmers and ranchers who are battling Knapweed in their fields.” 

One of the benefits to using insects to fight a Knapweed infestation over a chemical-based approach is the effect on the usable land for property owners. Not shrouding everything with chemicals generally leads to more viable soil, eventually equating to more grass for healthier, and more marketable livestock. Another obvious benefit is an organic approach to weed control that is not bound to a single application site, as well as a more cost-efficient alternative. 

“We want to help rid the local populations of this invasive species and to help put money back in the pockets of those ranchers and farmers,” Vaile said. 

There are three main stages to these plants dying out and patience is a key component to that process. The first phase takes roughly three to four years to complete, during which the insects, generally a breed of the Root Weevil family, will take shelter in the flower and begin to feed. This leads to a spotty appearance of the Knapweed and a halt in the spread of the plant as the insects eat the seeds and reproduce before transitioning into stage two. 

This next phase leads to substantially weaker plants as the larvae of the insects continue to eat through to the root of the Knapweed, ultimately weakening it before completely dying out in the final stage. 

“Our approach to biocontrols is very long-term and we have worked hard at chemical and mechanical control as well with success,” Montana rancher and biocontrol advocate Colleen Gustafson said. “However, new seeds are continuously moving in … we feel we must establish an insect population to have any hope for long term control.” 

Vaile and his insectary have received support from the local community as well as the Blackfeet Indian Reservation. They have had dozens of individuals donate their time to collect insects, with volunteers coming from the surrounding area as well as the Blackfeet Community College in Browning. Public seminars and workshops for those interested in learning more about the impact of an insect-based fight against invasive weeds have also been held in the past. 

“It takes time for the insects to do their work, but after three to four years you really start to see a difference in the reduction of Knapweed in fields,” Vaile said. “After the weed’s ability to dominate other plants dies, the native grasses return to the area and make for healthier soil and property. We want people to know about this process and to know that using bugs is better for you and for country.” 

As for Gustafson, her eyes are set on the future. 

“We feel that if we have a healthy population of insects established, our rangelands can remain healthy for the next generations,” Gustafson said. “Looking at the vast amount of Knapweed, they may be our only hope of maintaining our native grasses and forbs.” 

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