Michael Jones, forestry advisor with the University of California Cooperative Extension, warned local officials about the invasive beetle’s spread. "We've confirmed infestations in Hopland, areas south of Ukiah, and Potter Valley, which is heavily impacted," Jones said. The beetle primarily targets Valley Oak, Blue Oak, and Oregon White Oak, preferring areas with white oak species.
Originating from Mediterranean regions in Europe, the Middle East, and North Africa, the Mediterranean Oak Borer was first detected in Napa County in 2019. According to the University of California’s Department of Agriculture and Natural Resources, the adult female beetles colonize oak trees by females boring into branches and trunks, creating intricate tunnel systems, known as galleries, where they cultivate fungal spores. These fungal gardens are essential for the beetles’ diet appear to contribute to the death of their oak hosts.
Experts have noted the beetle’s unique behavior in California, specifically its tendency to colonize trees from the top down. In its native habitat, it doesn’t act this way. “Here, it’s rapidly killing large valley oaks, which are crucial to our urban forests," Jones explained.
Supervisor Glenn McGourty raised concerns about the beetle’s aggressiveness. "Is it targeting weak or damaged trees, or is it virulent enough to go after healthy ones?" he asked. Jones responded, "This beetle mainly attacks stressed trees, like those affected by drought and wildfires. But, given the stress our urban trees are under, it’s popping up across many different systems."
The beetle will exacerbate tree mortality, with Mendocino County already grappling with around 1.3 million dead trees. Supervisor John Haschak inquired about the impact of climate change and drought on the beetle’s spread. Jones confirmed that climate factors are likely contributing, but reassured officials that the beetle won’t target conifers, as it is specific to the white oak section.
Officials urge residents to take precautions to prevent the beetle's spread, especially through the movement of infested firewood. The U.S. Forest Service recommends buying firewood locally and burning it on-site. Those suspecting infestations can report sightings to the California Department of Food and Agriculture or their county agricultural commissioner’s office. Angela Godwin is the Agriculture Commissioner of Mendocino County and her number is 707-234-6830.
For more information, visit the California Department of Food and Agriculture's website or call the pest hotline at 1-800-491-1899.
