The race is on to stop a small pest from killing Southern California’s native oaks – San Gabriel Valley Tribune

Sage surrounds an oak tree in Newhall on Tuesday May 7, 2024. The golden-spotted emerald oak borer has been found infesting oak trees in the Newhall area. (Photo by Sarah Reingewirtz, Los Angeles Daily News/SCNG)

It’s less than half an inch long, but it can take down a giant oak tree in no time.

The golden-spotted emerald oak borer, GSOB or Agrilus auroguttatus, is a 0.4-inch bullet-shaped beetle with six golden spots on its forewings, and it burrows into mature oak trees, cutting off water and nutrients from the tree and leaving it to shrivel and die at the after about three years.

This new type of beetle native to the mountains of southeastern Arizona has been present in Southern California for only 20 years and the region has not adapted to the danger. The beetle is estimated to have killed 80,000 oak trees from Mexico to Southern California, primarily in San Diego County.

On Tuesday, May 7, the Los Angeles County Board of Supervisors passed a motion to consider declaring a state of emergency and hiring a deputy forester and two assistants to search for GSOB in trees on state, federal, county and private. The motion also calls for working with CalFire and other agencies on testing, monitoring, treatment and reforestation.

“This small, invasive pest poses a big threat. I strongly believe that our county must make efforts to proactively protect our majestic oak forests from infection and death,” said Fifth District Supervisor Kathryn Barger.

This deadly pest travels from one place to another by hitchhiking in bundles of firewood. The densest infestations are seen in firewood-burning communities, usually in the mountains, where people burn oak wood in fireplaces, on outdoor campfires, or at campsites.

A report will be submitted to the council with a proposed county ordinance that regulates the movement of firewood, perhaps preventing transportation, and allowing the sale of the wood only where it was cut from dead trees. “So the firewood stays where it was produced,” said Rebecca Ferdman, policy director for the Los Angeles County Chief Sustainability Office.

“This motion takes steps to prevent an infestation of the emerald oak borer, recognizing the value of oak trees to the vitality of our forested areas,” said a co-sponsor of the motion, Third District Supervisor Lindsey Horvath, in an email response.

GSOB only infests oaks, namely the three oaks native to California: the coast live oak, the canyon live oak, and the California black oak. These are the most common trees that make up the tree canopy of Southern California.

Research shows the burrowing pest 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, fire crews from Los Angeles County and CalFire have removed 1,500 dead trees since 2015, with another 400 infected trees yet to be removed, Ron Durbin, the state’s forestry service chief, said Monday. Los Angeles County Fire. , May 6.

New evidence indicates that some oak trees at East and Rice Canyon and Whitney Canyon in Newhall, just north of the junction of Highways 5 and 14, have been infected, said Durbin, who did not know the extent of the infestation at this place. “It’s very early,” he said. “We’re trying to recruit the people we need to do the investigation and understand the full extent of it. »

The infestation quickly moves to other oak-covered land. The virus traveled 20 miles from Green Valley to the forested canyons, likely thanks to someone carrying firewood, Durbin said. His team fears the GSOB could reach the Chatsworth Nature Preserve, an area with many LADWP-owned oak trees in Chatsworth, an unincorporated town, in the San Fernando Valley. For now, this area is not infested, he noted.

But the residential community around this reserve is a firewood burning community – which is concerning. “Firewood is the fastest way for GSOB to move through a community. People don’t know the 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 from the Chatsworth Preserve, it could trigger an infestation that would eliminate 600,000 live oaks from the coast. A county report named a potential GSOB infestation in the Santa Monica Mountains as the “worst-case scenario for Los Angeles County.”

“Oaks are essential to the biodiversity of the Santa Monica Mountains and their health is something we need to protect,” said Horvath, whose district includes the 153,000-acre SMM Natural Recreation Area, which includes canyons dotted with chaparral and oaks, 500 miles away. 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. San Bernardino County CalFire crews are removing dead trees to stop the spread. The annoying 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 Idyllwild in Riverside County, Durbin said.

The pest has a cruel modus operandi.

“He loves the biggest, most glorious majestic trees, that’s all he loves,” Durbin said. If it reached the Santa Monica Mountains, it could be a disaster: “It would completely change and destroy this ecosystem if no measures are mitigated,” Durbin said.

In large trees with wide bark, hundreds of larvae feed on the cambium – the living tissue of the tree – so that the tree can no longer receive nutrients and water. The tree dies of starvation, first losing all its leaves. Then the sap emerges in a failed effort to defend itself. Finally, the adult GSOB digs a hole in the bark and emerges.

“New adults emerge from the tree and head to the next available oak,” Durbin said.

LA County Fire and CalFire also use systemic pesticides that they inject into the base of the infected tree in order to save infected trees. Efforts have been underway in Green Valley for 9 months, he said. “So far we’ve had pretty good success, but it’s too early to see if it works,” he said.

Climate change, bringing more heat, can stress some oaks. This can make them more vulnerable to exotic pests, Ferdman said. With this motion, Horvath is seeking a longer-term strategy, Ferdman said.