Goldspotted Oak Borer

Goldspotted Oak Borer (GSOB) is an invasive pest that is accounting for large numbers of oak tree mortalities throughout San Diego County. GSOB is now spreading to Orange and Riverside counties as well.

GSOB adults feed on oak foliage. Females lay eggs in cracks and crevices of the oak tree’s bark. Once eggs hatch, larvae burrow into the tree where they feed beneath the bark of the trees. Larvae feeding will kill sections of cambium, which eventually results in tree death.

It is highly recommended if you are in a “GSOB Zone of Infestation (ZOI)” to have a management plan in place for GSOB control.

Any Oaks showing decline/ discoloration or symptoms of GSOB prior to treatment may not fully recover.

Any Oaks showing advanced stages of decline (40% +), and rapidly discoloring foliage should be evaluated for removal immediately, in effort to reduce possible spread to nearby oaks.

Along with suggested treatments, reducing plant stress by properly irrigating along the mid to outer drip line with deep and infrequent irrigation Fall – Spring. Also reducing large cuts or pruning during Spring-Fall when pests are most active.

GSOB management suggestions by UC IPM’s Goldspotted Oak Borer Field Identification Guide:

  • Preventing movement of infested wood (primarily firewood) to new areas is essential for slowing the spread of this exotic borer to other regions of the state.

  • Contact insecticides applied prior to GSOB adult activity, which begins in early to mid-May. Contact treatments should be applied to the main stem and large diameter branches to reduce numbers of GSOB adults and their egg laying. Trees should be re-treated every year until additional data is collected regarding the duration of efficacy.

  • Although woodpeckers are known to forage on (GSOB) Goldspotted Oak Borer larvae, their feeding is not sufficient to significantly suppress populations. No other significant natural enemies of the pest are currently known in California.

Management & Treatment

It’s important to note that if your oaks are candidates for insecticide treatment, that a trained, qualified and licensed pest control applicator makes the application. Certain insecticides are restricted and improper applications can have significant negative impacts on natural enemies, bees, wildlife, and water quality.

APC is a GSOB treatment specialist and has all the required licensing, experience and knowledge to help treat your oaks for GSOB control.