What to Know About The Goldspotted Oak Borer

Goldspotted Oak Borer


Black or iridescent green with golden yellow spots


About 10mm long and 2mm wide with a bullet-shaped body

Known Host

Coast Live Oak, California Black Oak, and Canyon Live Oak


Does not travel far on its own, typically is transported to new areas through infected firewood


Goldspotted oak borer (GSOB) Agrilus auroguttatus is an invasive pest contributing to the on-going oak tree mortality occurring across San Diego, Riverside and Orange Counties. First discovered in San Diego in 2004 by the California Department of Food and Agriculture, the Goldspotted Oak Borer prey on drought-stricken trees with lowered immunity, where they begin to feed under the bark. The GSOB burrows deep in the core of the tree, laying larve, cutting off water supply, and attacking one branch at a time until the tree is completely dead. Trees that have been infected to the point of death are safety hazards for passers by, since they are unstable and likely to fall at anytime.


How to Recognize Infected Wood

Crown thinning and dying branches are usually an initial indicator of moderate to severe infestation. A healthy Oak will exhibit full thick leaves at the top, but as infestation occurs and progresses, branches and leaves will begin to die and thin. Unlike some other wood-boring Agrilus species, GSOB does not attack the upper branches in the crown during the early stages of infestation. The GSOB adult emergence holes(approximately 0.15 inches indiameter) can appear before any other injury symptoms are observed, providing for early diagnosis. As many as 70 percent of the oak trees in these areas are thought to be infested. Evidence of insect attacks on oak trees can also be detected by:  

  • The presence of the insects under the bark 
  • D-shaped exit holes 
  • Woodpecker foraging (typically to eat GSOB located under the bark)
  • Dark colored wet staining or red bleeding
  • Crown color of tree from dark green (healthy) to grayish green (severely injured) 


How to Stop the Spread of Infestation

Research efforts are directed at assessing the oak borer’s current distribution and life cycle in southern California, effective survey techniques, treatment options for high-value trees, factors enhancing tree susceptibility, and firewood management. What is currently known about them is that they remain in a localized area jumping tree to tree but do not travel long distances on their own. This means that their relocation relies on the transportation of their species through firewood. The Forest Service is requesting that recreational users do not transport firewood from the location or purchase or procurement, but instead to "Burn it where you buy it" and keep the wood (and the pest) localized.


How to Protect Your Oaks

Drought-striken and stressed trees are increasingly vulnerable to the GSOB infestation, and with weakened immune systems trees are unable to produce the sap required to fend off invasion. If possible, keep your oaks hydrated, or consider applying a pesticide. A contact insecticide applied to the main stem and to the larger branches (>8 inches in diameter) is the best option for preventing GSOB injury. Contact spray applications should occur in May prior to the adult flight period in southern California and be re-applied annually by a certified pesticide applicator. Avoid bringing wood on your property that has been purchased in other locations as any close proximity within half mile can affect the oaks. If you must bring in firewood, be sure to ask the vendor where they obtained the wood and inspect it for signs of infestation.


What to do if Your Wood is Infected

If you suspect that you have found signs of GSOB or symptoms of its damage on your property, please contact the University of California's Cooperative Extension Office, the County Agricultural Commissioner’s Office (San Diego County, Orange County, or Riverside County), directly to the Cleveland National Forest, or your local Forest Health Protection representative.

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