New Invasive Beetle Detected In This Bay Area County

NOVATO, CA — An invasive insect that can wipe out trees was found in Novato, the County of Marin stated Monday.

The Mediterranean oak borer, which primarily feeds on white oaks, was detected in Marin County, prompting the Marin County Agricultural Commissioner and the Marin office of the University of California Cooperative Extension to notify arborists and the public to keep an eye out for evidence of this tree pest.

Joe Deviney, Marin’s Agricultural commissioner, said the beetle was identified in a valley oak on May 23. The insect — native to Europe, the Middle East, and North Africa — was first detected in 2019 in Napa County. It has since been found in nine other counties.

“Education about the beetle is important, but unfortunately it can’t be eradicated and it’s becoming more widespread in our area,” Deviney said. “It was only a matter of time for the presence of this invasive pest to be confirmed in our county.”

Deviney encourages homeowners to monitor tree crowns, and, if they see a decline in leaf growth or observe other symptoms of an infestation, to seek expert evaluation from a certified arborist.

Marin County departments are collaborating with California pest management and wildfire agencies to detect, study and educate about the borer.

Tiny ambrosia beetles, which are about 3 millimeters or one-eighth of an inch, bore tunnels into stressed oaks, primarily valley oaks, but also Oregon white and blue oaks.

They start in branches, eventually reaching the trunk and killing the tree. The beetles carry and feed on fungus grown in their tunnels, allowing them to live and reproduce within the tree for generations.

While the fungus can cause disease, the beetles typically target already stressed or declining trees, a common scenario in California oak groves and forests.

Deviney is working with the UCCE, which provides programs on agriculture and natural resources, forest health, horticulture, and human-wildlife interactions among others.