Two tiny adult goldspotted oak borer beetles sit on a penny. The invasive pest, first found in San Diego County in 2008 has now been found in Ventura County and is believed to be spreading northward. Photo courtesy University of California
An invasive species of beetle that attacks oak trees, first detected in 2008, has made its way to Ventura County, and CAL FIRE is warning everyone to watch out for it as it moves north.
“CAL FIRE and the Mountains Recreation and Conservation Authority,” reads a notice from CAL FIRE, “have confirmed multiple new detections of the invasive goldspotted oak borer [GSOB] in Ventura County, marking a significant expansion of the destructive pest’s presence in the State of California.”
The first GSOB-infested live oak tree was found in August 2024 in Ventura County’s Box Canyon, which is on the eastern edge of Ventura County. That tree was cut down and properly disposed of to avoid spreading the pests.
A second, dead and infested oak tree was found in Santa Susana in April 2025, CAL FIRE said. They soon discovered a row of oaks killed by the borers last May along Las Llajas Canyon Road, also in Ventura County.
The borers were first discovered in California in San Diego County in 2008. Since then GSOB has killed more than 200,000 mature oak trees in San Diego, San Bernardino, Riverside, Orange, Los Angeles and now Ventura Counties.
These nasty beetles have help. “The invasive beetle continues to spread largely through the movement of infested firewood.”
California’s oak woodlands are among the State’s most treasured and important natural habitats and are highly vulnerable once the borers invade, killing a mighty oak tree within a few years of being infested.
Some 80,000 oaks in San Diego County’s Cleveland National Forest have already been killed.
The beetles are native to oak woodlands in Arizona and Northern Mexico, where they are kept in check by natural predators.
Adult beetles feed on the tree’s leaves, and bore into an oak tree’s bark to lay eggs. Larvae hatch and feed on the inside of the trees, essentially cutting off the tubes that move nutrients from the roots into the upper tree.
With thousands of small, worm-like larvae feeding on a single tree they can kill what is perhaps a 150-year old tree in 2-3 years.
CAL FIRE and several agencies and universities are working together to fight the pest and are encouraging everyone to be on the look out for early signs (dying oaks) and “to avoid transporting firewood from GSOB infested areas.” Firewood from Arizona is thought to be the likely vector that brought the beetles to California.
Firewood is a common way such pests migrate, for example firewood is suspected of playing a big role in the spread of the pine pitch canker that killed thousands of Monterey pines in SLO County back in the 1990s.
A good rule of thumb for campers is to burn it where you bought it and don’t take firewood with you when leaving one natural area for another.
To learn more see the website at: www.gsob.org.
