Knapweed & Toadflax Biological Control

The Knapweed seed head weevil Larinus minutus and the stem-mining weevil, Mecinus janthinus, are two highly effective biological control agents when it comes to suppressing Diffuse knapweed and Dalmatian toadflax. These two biological agents are unequivocally the most destructive of all the insects released against knapweed and toadflax in North America thus far. 

The insects are host specific which means they will only attack knapweed and toadflax, they are self perpetuating, have the ability to fly and find weeds nearby in an area and are ecologically desirable and cost effective. They readily survive in most sites where released and will start impacting the two weed species immediately. 

Program Goal

The goal of any biological control program is to shift the competitive balance away from he target weed to desirable grasses and forbs.

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Washington State University (WSU) Douglas County Extension has been working with Douglas County, FSA and Foster Creek Conservation District to identify and release these beneficial insects in infested area. If you think you have an area that could benefit from the release of biological control please contact Dale Whaley, WSU Extension Educator at 509-745-8531.