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Weed board says root weevil shows strong local effect; gall wasp results mixed after grasshopper losses
Summary
Staff told the board root‑feeding weevils released for knapweed control are producing about an 80% kill rate locally, while gall wasps have not yet shown a visible kill rate and last year's releases were heavily predated by grasshoppers.
Staff reviewed the biological‑control effort the board used against knapweeds and related species, reporting that root‑feeding weevils obtained through Soil Conservation are proving effective and yielding approximately an 80% kill rate on knapweed in Duchesne County. "The root weevils have it's about an 80% kill rate right now in Duchesne County," the staff member said, adding that some counties see 90–100% spot kill where conditions are ideal.
By contrast, staff said gall wasps targeted to Russian knapweed have not yet produced an observable kill rate; last year the board lost an estimated 95% of released biological agents to grasshopper predation. Staff described multiple release events this year to rebuild populations and said they are establishing collection and release sites in Bridgeland and Fruitland to sustain populations.
