Lake County supervisors heard an update Wednesday on the invasive Mediterranean oak borer and its rapid toll on valley and blue oaks across the county. Presenters from Cal Fire and the Clear Lake Environmental Research Center told the board that the insect has been confirmed in multiple counties and is killing large, older valley oaks—the county's keystone tree species.

The presentation said researchers, tribal environmental programs and county staff are expanding mapping and surveys, planning contractor and arborist training in early December, and lining up treatment trials and grant applications to slow the pest's spread. Tribal representatives urged the county to protect cultural resources and to monitor any pesticide work so it does not contaminate acorns or gathering sites.

Why it matters: valley oaks support thousands of species and are culturally important to local tribes, speakers said. County and federal aerial-survey figures cited in the meeting note large-scale tree mortality from multiple causes; presenters warned that Mediterranean oak borer could greatly increase oak loss unless community reporting, careful removal of infested wood and funded mitigation are scaled up.

Terry Logsdon, Lake County chief climate resiliency officer and tribal liaison, introduced the update and said representatives from Cal Fire, the Clear Lake Environmental Research Center and UC Cooperative Extension would present the latest findings. Cal Fire entomologist Curtis Hewing said the beetle's spread accelerated this year and that surveys show the insect in at least nine to ten California counties. "The rate of spread in California has really been picking up," Hewing said.

Hewing described the species' seasonal dispersal trigger: adult movement begins when sapwood reaches roughly 65 degrees Fahrenheit and can be triggered by brief warm spells. He said dispersal this year occurred as early as February and continued into June in parts of the state. Hewing said researchers are tracking about 300 trees in six plots and that "this year is the first year we have seen a number of trees that appear to be recovering." He cautioned that the observation is preliminary and that firm data are not yet available.

UC Cooperative Extension forest adviser Michael Jones said treatment trials are being planned with commercial arborists and companies that perform tree injections. Jones said the initial candidate chemicals under consideration include the insecticide abamectin (abamectin benzoate) and phosphorous acid as a fungicide, plus products used for ambrosia-beetle complexes. "Wehaven't really come up with all the research trials we're gonna do yet," Jones said, adding that the trials will include monitoring to assess whether treatments move into acorns.

Presenters and commenters repeatedly identified movement of infested wood and firewood as the primary long-distance vector. Hewing said the large, discontinuous jumps of the pest observed between counties are "almost certainly the movement of wood." The discussion included practical disposal guidance discussed by presenters: burying infested material to about eight inches and avoiding coarse chipping that may allow a small percentage of insects to survive. Hewing estimated, "Up to 5% maybe would be a guess," for survival in improperly handled chips, and said more data are needed.

County staff and the Clear Lake Environmental Research Center described mapping and outreach underway. The clerk's office has a public reporting dashboard and map at clerk.org that color-codes current and prior-year reports; the presenters asked residents and contractors to report suspected infestations. A contractor training for identification and safe handling of infested woody material is planned for early December (tentatively the week of Dec. 8), and UC Cooperative Extension plans a public meeting with Middletown Rancheria in late November. Jones also said the research team will apply for grants and form a work group to coordinate monitoring and response.

Tribal speakers emphasized cultural and subsistence concerns. Dimitri Novoa, EPA technician and tribal member with the Scotts Valley Band of Pomo Indians, told the board: "The oaks are very important to us. It is one of our cultural foods" and said tribes want to be included in planning. Big Valley Band of Pomo Indians environmental director Sarah Ryan asked about active ingredients and potential impacts on acorns; Jones said researchers will include monitoring for acorn contamination and that the chemicals they plan to test are not expected to move substantially into nuts based on existing studies.

Public commenters urged stronger local outreach, coordination with PG&E and its contractors to limit tool- and wood-borne spread, and use of traditional cultural burning and stewardship. Speakers also raised permitting issues: a presenter noted the City of Clearlake has an ordinance requiring proof before removing an oak tree; county-level discretionary permit review and outreach to property owners were suggested as local actions to keep healthy oaks standing.

No formal action or vote was taken during the presentation. Board members and presenters said next steps include expanding surveys in 2026 with recently secured funding, completing the contractor training in December, developing grant proposals for treatment trials and woody-biomass disposal, and continuing community mapping and outreach through the clerk's dashboard. Staff said they will coordinate with tribal partners, UC Cooperative Extension and Cal Fire as those initiatives advance.

For more information and to report suspected Mediterranean oak borer sightings, presenters directed residents to the county reporting page at clerk.org and to upcoming local events and trainings announced by UC Cooperative Extension and the Clear Lake Environmental Research Center.