The oaks in the Valley might be in grave danger of infestation and destruction.
According to Jess Stoffel, vegetation manager for the County of San Diego, the gold-spotted oak borer (GSOB), or agrilus coxalis, was first detected in the area in 2004 during a trap survey for invasive tree pests.
GSOB, which is a native to Arizona and Mexico, was likely introduced into southern California via infested oak firewood. Roger Boddaert, known as “the tree man” of Fallbrook, stated that he is “very much aware” of this pest and other infestations.
“Primarily, there are four main species the borer is attacking, including our indigenous coastal California Live Oak,” said Boddaert. “I recently attended a conference at the Pechanga Government Center on the borer and other native oak concerns. There was a large attendance from the US Forest Dept., UC Davis and Riverside, and all the major players in this major concern.”
It is a serious pest of coast live oak, Quercus agrifolia; canyon live oak, Q. chrysolepis; and California black oak, Q. kelloggii in California and has killed more than 20,000 trees across 620,000 acres.
Boddaert stated that the GSOB have been identified in Julian, southern San Diego County, and primarily in the mountain ranges.
“We had one isolated case in La Jolla, which occurred because individuals went into an infested area, cut down trees, and brought down firewood,” he explained. “That is the main culprit in transporting GSOB from one area to another. If wood is carried from an infested site, then the larva and eggs can be transmitted throughout the state. That is the fear of the agricultural community; we can start losing our native trees, disrupting the ecology of the oak woodlands and creek beds dotted around North County.”
To date, GSOB-killed oaks have only been found in San Diego County; however, it is expected that the area of infestation will continue to extend north beyond the county line and tree mortality will continue to increase due to adult flight from infested trees and new infestations initiated through beetles emerging from transported firewood.
“This is something that is pretty feared in the environmental world,” said Boddaert. “Once the borers set up house, they eat their way out at the tissue where water flows up and down the plant. Trees can die within a short amount of time.”
One indicator that firewood or trees have been infested is a hole entry that is shaped like a capital ‘D’, said Boddaert. Another is excessive “bleeding” or oozing from the tree.
“I am in the process of working with government agencies to establish a forum in Fallbrook,” he said. “The date is not determined, but my goal is to get citizens to come on a volunteer basis and learn how to identify [these pests.]”
For more information on the gold-spotted oak borer, go to