The race is on to stop a tiny pest from killing Southern California’s native oak trees
It’s less than a half-inch long but it can fell a giant oak tree in no time.
The goldspotted oak borer, GSOB or Agrilus auroguttatus, is a 0.4-inch bullet-shaped beetle with six golden spots on its forewings, and it burrows its way into mature oak trees, cutting off a tree’s water and nutrients and leaving it to shrivel and die in about three years.
This new kind of beetle pest with origins in the southeast Arizona mountains has only been in Southern California for 20 years and the region has not adapted to the danger. The beetle is said to have killed 80,000 oak trees from Mexico to Southern California, mostly in San Diego County.
On Tuesday, May 7, the Los Angeles County Board of Supervisors passed a motion that explores declaring a state of emergency and hiring a deputy forester and two assistants to seek out the GSOB in trees on state, federal, county and private lands. The motion also calls for working with CalFire and other agencies on testing, monitoring, treatment and reforestation.
“This tiny invasive pest is a big threat. I firmly believe our county needs to put its muscle behind proactively protecting our majestic oak forests from infection and death,” said Fifth District Supervisor Kathryn Barger.
The deadly pest moves from one place to another hitchhiking in bundles of firewood. The most dense infestations are seen in firewood-burning communities, usually in the mountains where people burn oak firewood in fireplaces or in outdoor campfires or at campgrounds.
A report will come back to the board with a draft county ordinance that regulates the movement of firewood, perhaps by preventing transport, and only allowing wood to be sold where it was cut from dead trees. “So the firewood stays where it was produced,” said Rebecca Ferdman, policy director with L.A. County’s Chief Sustainability Office.
“This motion takes steps to prevent an infestation of the goldspotted oak borer, recognizing how valuable oak trees are to the vitality of our forested areas,” said a co-author of the motion, Third District Supervisor Lindsey Horvath, in an emailed response.
The GSOB only infests oak trees, namely the three native to California: coast live oak, canyon live oak and the California black oak. These are the most prevalent trees that make up Southern California’s tree canopy.
Research shows the burrowing pest has felled trees in Green Valley, a community of about 1,000 people in the Sierra Pelona Mountains 19 miles west of Palmdale and 20 miles north of Santa Clarita. There, teams of workers with the Los Angeles County Fire Department and CalFire have removed 1,500 dead trees since 2015, with another 400 infected that have yet to be removed, said Ron Durbin, chief of forestry for the Los Angeles County Fire Department, on Monday, May 6.
New evidence indicates some oak trees in East and Rice Canyon and Whitney Canyon in Newhall just north of the junction of the 5 and 14 freeways have been infected, said Durbin, who did not know the extent of infestation there. “It is very early,” he said. “We are trying to get the people we need to do the surveying, and understand the full extent.”
The infestation is moving to other oak-studded land quickly. The bug made the 20-mile jump from Green Valley to the forested canyons, most likely by someone carrying firewood, Durbin said. His team is concerned the GSOB could reach the nearby Chatsworth Nature Preserve, an area of many oak trees owned by LADWP in unincorporated Chatsworth in the San Fernando Valley. So far, that area is not infested, he noted.
But the residential community around that preserve is a firewood-burning community — a concern. “Firewood is the fastest way the GSOB moves in a community. People don’t know it (firewood) is infested and they will bring it into their community. Then the insect emerges from the firewood,” Durbin said.
If the GSOB reached the Santa Monica Mountains National Recreation Area, just 14 miles away from the Chatsworth preserve, it could begin an infestation that would wipe out 600,000 coast live oak trees. A county report named a potential GSOB infestation in the Santa Monica Mountains as the “worst case scenario for Los Angeles County.”
“Oak trees are essential to the biodiversity of the Santa Monica Mountains and their health is something we must protect,” said Horvath, whose district includes the 153,000-acre SMM Natural Recreation Area, which includes chaparral and oak-tree studded canyons, 500 miles of trails and 46 miles of California coastline.
The pest has infected trees in the mountain town of Wrightwood in the eastern San Gabriel Mountains, Durbin said. CalFire teams from San Bernardino County are removing dead trees to stop the spread. The boring insect has reached oak trees in Orange County’s Great Park, as well as in Oak Glen, a mountain community in San Bernardino County, and in Idyllwild in Riverside County, Durbin said.
The pest has a cruel modus operandi.
“It likes the largest, most glorious majestic trees, that is all it likes,” Durbin said. If it reached the Santa Monica Mountains, it could spell disaster: “It would completely change and destroy that ecosystem if it goes unmitigated,” Durbin said.
In large trees with wide barks, hundreds of larvae feed in the cambium — the living tree tissue — so the tree can no longer receive nutrients or water. The tree starves to death, first dropping all its leaves. Next, sap emerges as part of a failed effort to defend itself. Last, the adult GSOB carves a hole in the bark and pops out.
“New adults emerge out of the tree and they go to the next available oak tree,” Durbin said.
L.A. County Fire and CalFire are also using systemic pesticides they inject into the base of the infected tree as a way to save infected trees. Efforts have been underway at Green Valley for the last 9 months, he said. “So far we’ve had fairly good success but it is too early to see if it is working,” he said.
Climate change, bringing more heat, can stress some oak trees. This can make them more vulnerable to exotic pests, said Ferdman. With this motion, Horvath is looking for a more long-term strategy, Ferdman said.