A pest responsible for killing more than 90,000 oak trees in San Diego County has been discovered in Idyllwild – the first confirmed find in the Inland region.
The gold-spotted oak borer has killed at least one California black oak in the Riverside County mountain community, Cal Fire spokeswoman Julie Hutchinson said Wednesday, Nov. 14.
A Cal Fire forester who lives in the area spotted the sickly tree on her way to work. Kathleen Edwards, who works on the beetle problem in San Diego County, noticed the leaves turning brown well before those on surrounding trees and suspected the gold-spotted oak borer.
“This tree was definitely standing out,” Edwards said. “It was completely different from the fall foliage.”
The tree, located along Highway 243 just south of town, was cut down Wednesday. It was taken to San Diego County for further study, Hutchinson said.
Crews also will begin surveying the area to determine the extent of the infestation. The bugs are transported in firewood.
Trees in affected areas can have a 90 percent mortality rate, said Tom Scott, an assistant professor of earth sciences and a natural resource specialist at UC Riverside who studies the beetle.
The infestation threatens 10 million acres of red oak woodlands in California, he said.
The loss of oaks is expensive in many ways. It diminishes shade, wildlife habitat and property values, and removing dead trees costs millions of dollars, he said. The dead trees also increase fire danger.
Most of the affected trees in San Diego County are 150 to 250 years old, with trunks up to 6 feet in diameter. Their removal can cost as much as $10,000 each.
Communities with oak woodlands, such as Riverside, Yucaipa and the Santa Rosa Plateau are at risk, he said.
“Idyllwild has already been devastated by pine beetles. Everybody should be concerned about having these beetles come into their community,” Scott said.
The half-inch-long beetle also attacks mature coast live oaks and canyon live oaks. Female beetles lay tiny eggs in the crevices of the bark, and the larvae burrow down, cutting off water and nutrients.
They can kill a tree in as little as a year, Scott said.
There is no successful treatment for the borer. Pesticides are being tested that could be used on a small scale for high-value trees, said Kevin Turner, gold-spotted oak borer coordinator for UC Agricultural and Natural Resources at UCR.
Grinding up the infested wood has been shown to kill the larvae, he said.
Officials warned residents to buy firewood where they plan to burn it and to not transport logs. If they have firewood and don’t know where it came from, it should be burned this winter before the pupae emerge, Turner said.
An aggressive “buy it where you burn it” campaign wasn’t enough to keep the gold-spotted oak borer from leapfrogging 40 miles north to Idyllwild, however. The beetle originally came from southeast Arizona in the 1990s, probably in firewood, but wasn’t confirmed in San Diego County until 2004.
“There are literally tens of thousands of cords of wood in San Diego County that probably still have beetle in them,” said UCR’s Scott. “We’re hoping this will be a wakeup call for anyone who wants to buy firewood.”
Cal Fire is working on a rapid response plan with the University of California, U.S. Forest Service and Riverside County to conduct surveys and educate residents in the San Jacinto Mountains.
Property owners in the Idyllwild area will be sent information in the coming weeks on the gold-spotted oak borer, how to check their trees for the pest and a list of contacts.
“We’ve been preaching for a long time of the need to be prepared for the gold-spotted oak borer’s move. We have a network of key players in place” Turner said. “Hopefully it will prevent this from spreading.”
Gold-spotted oak borer
ORIGIN: Native to southeastern Arizona
TRAVEL: Transported in firewood
CALIFORNIA: Showed up in San Diego County in the 1990s
DESTRUCTION: Killed more than 90,000 oaks in San Diego County
AT RISK: 10 million acres of red oak woodlands in California
TREE DAMAGE: Larvae burrow under bark, cutting off water and nutrients and killing the tree
TARGETS: California black oaks, coast live oaks, canyon live oaks
Source: UC Riverside