The Pest That's Destroying Southern California Oak Trees
The Gold Spotted Oak Borer (Agrilus auroguttatus) is a flat-head borer which attacks native California oaks in San Diego and Riverside counties. The insects attack coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), interior live oak (Quercus chrysolepis), and in rare cases Engelmann oak (Quercus engelmannii). They have killed over 80,000 native oaks so far.
GSOB is thought to produce only one generation per year in Southern California. Adults bore out of the tree from mid-May through September to find a mate. Peak flight period for GSOB adults is from June to July. The adult female lays her eggs in the cracks of the bark on the tree. The eggs hatch about two weeks after being laid. GSOB larvae bore into the tree where they stay and feed inside the tree until the following spring when they emerge as adults. Learn more about the Gold Spotted Oak Borer on the UC Davis Integrated Pest Management webpage.
How to Recognize GSOB Damage
D-shaped holes, about a quarter of an inch in length will appear on the lower twenty feet of the oak's trunk. The presence of the GSOB larvae is indicated by black wet staining or dark red "bleeding" on the trunk. There will also be thinning in the tree's upper canopy.
Gold Spotted Oak Borer Treatment Protocol
To be most effective in treating these insects, both adults and larvae need to be targeted. Barrier treatments timed just prior to peak adult GSOB flight time is crucial (May-July). The adults have to chew through the barrier treated bark in order to exit the tree. A systematic treatment for the larvae that may already be inside of the tree is extremely important. Larvae feeding inside of the tree is what produces tree mortality - they consume the vascular tissue of the tree as they mature.
Arborwell offers three levels of treatment to help protect the value of your native California oaks be managing the pest and the damage it creates.