A hungry pest called the goldspotted oak borer is devouring enormous numbers of oak trees in San Diego County, and its devastation could spread to trees throughout California, according to researchers at UC Riverside.
More than 80,000 oak trees in the county have been killed in the past decade. Unless the march of the half-inch-long beetle is stopped, it could threaten 10 million acres of red oak woodlands in the state, researchers said.
“This may be the biggest oak mortality event since the Pleistocene (12,000 years ago),” UC Riverside natural resource specialist Tom Scott said in a report issued this week.
The goldspotted oak borer is native to Arizona but may have immigrated to California in a load of infested firewood, Scott said. Dead trees have been found from the backcountry communities of Descanso and Guatay to the seaside neighborhood of La Jolla.
So many trees have died in the Burnt Rancheria campground in the Cleveland National Forest that the U.S. Forest Service has erected shade structures for campers in lieu of what was once a canopy of coast live oaks.
The live oaks, black oaks and canyon live oaks seem defenseless against the goldspotted oak borer, and the beetle has no natural enemies to keep it in check.
The females lay eggs in the trees and the larvae burrow into the interior. Adults bore through the bark. The trees turn brown and die.
The UC Riverside researchers, the UC Cooperative Extension, UC Agricultural and Natural Resources, the Forest Service and other agencies are working with woodcutters, arborists and consumers to discourage the transportation of infected wood from San Diego County to other locations.
Firewood production is one of the least regulated industries in California, said the researchers, who have received $635,000 of a $1.5-million federal grant to study the sudden oak death.
— Tony Perry in San Diego
Photo: A goldspotted oak borer. Credit: UC Riverside