Oak-Killing Beetle Moves West to San Diego

A new report by the U.S. Forest Service confirms that gold-spotted oak borer beetles have been found at Marian Bear Memorial Park in Clairemont, 45 miles west of where the agency first confirmed an infestation in 2008.

A bug that has killed more than 20,000 oaks in the backcountry has made a beachhead in suburban San Diego, raising the specter of tree die-offs across neighborhoods and parks in the county and beyond. The insect also has been reported in Crest and the western edge of Ramona. The trees it kills could feed wildfires, lower property values and change the natural landscape of the metropolitan area. Oak mortality in areas infested by the beetle averages 65 percent and is close to 100 percent in some spots.

Researchers for the Forest Service said the bullet-shaped insect has spread across 620,000 acres in the county and is likely to expand its range as adults fly outward and young beetles emerge from firewood that is shipped elsewhere. So far, agricultural officials haven't established quarantines to halt the movement of wood from affected areas partly because the borer doesn't threaten a commercial food crop. Everyone involved with the control effort urges residents to avoid transporting oak firewood around the region, but they acknowledge that people likely will continue doing so as long as they can keep making money from wood sales.

Roughly 39 million acres of oak habitat statewide may be vulnerable, the Forest Service said. For now, the insect has only been identified in San Diego County.

Oaks are a defining feature in about 125 communities across Southern California, many of which have rules to protect the long-living trees.

More than a dozen varieties of the tree dot San Diego County, and at least three are targeted by the gold-spotted beetle. Coast live oaks, canyon live oaks and California black oaks range from the mountains of East County to the coastal lowlands. Such species are prominent in grasslands near Ramona and open spaces such as Live Oak Park in Fallbrook and the Marian Bear greenbelt along state Route 52.

San Diego park officials said they are waiting for recommendations from the Forest Service and others before taking measures against the beetles at Marian Bear. Federal scientists have set traps at the spot to get a better handle on the infestation. Meanwhile, the costs of cleaning up after the pest are mounting.

California State Parks has spent more than $52,000 since 2008 to remove dead oaks and lost an estimated $400,000 in revenue because some camp sites had to be closed because of the hazard from dead and dying oaks, the Forest Service said. The Resource Conservation District plans to start a $3 million tree-removal program in July for dead oaks in and around Descanso. That's just a sliver of the area that could be munched by the bugs.

The UC system and its partners are preparing to ask master gardners and other residents to systematically look for signs of the beetle. The Forest Service's plans for this year include placing traps in the southern Sierra Nevada and the Central Valley. Infested trees typically lose their top leaves, creating what arborists call a thin crown. D-shaped exit holes in the bark are another sign.Typically, the oaks can't be saved by the time an infestation is detected. Besides their aesthetic value, oaks are an integral part of the ecosystem. Their acorns are eaten by livestock, deer, rodents and wild turkeys, while woodpeckers store nuts in them and a certain type of ant lives only in oak trees.

If oak deaths go unchecked, ''there could be a cascading effect from one species to the next,'' said Jon Rebman, curator of botany at the San Diego Natural History Museum. ''It would be devastating ... especially after we have already had a significant hit on our pine forests because of the (wild)fires'' in 2003 and 2007.