When we moved from the San Diego area nearer to Los Angeles, old coast live oaks — the native oak that epitomizes California – were dying off from a new pest. We lived in the east part of San Diego County and were concerned about the pest as we heard reports of it moving westward. Especially since our property had a half-dozen 80-year-old oaks on our property.
Unfortunately, the beetle – the goldspotted oak borer or GSOB– that is causing this is moving north as well as west. Three oaks 30 miles away are infectected in Idyllwild CA.
Firewood is the culprit
The pest was likely moved in firewood transported from an infected source in San Diego County. This is a significant concern, as it’s believed the pest moved within San Diego County several times on firewood.
The good news is there are measures people can take to keep it from moving. The biggest one recommended by the U.S. Forest Service is “Buy It Where you Burn It.”
Only buy local firewood.
Do not buy it from unknown sources selling wood on the side of the road. It must be cut locally. (This a always a good rule of thumb. The Emerald Ash Borer that is devastating ash trees is transferred via firewood)
Some info about this issue:
- The goldspotted oak borer (GSOB) is not native to California. The wood borer is native to southeastern Arizona where it has not become a pest. For some reason it has become problematic to oaks in California
- It prefers trees with thick cambium (the living tissue that forms the rings in a tree) which it can burrow into – therefore the oldest oaks. The beetle leaves a dark black or red stain and a D-shaped exit hole.
- Once a tree is infected, evidence suggests it will die.
- GSOBs are very good fliers and can fly up to 10 miles at a time, but commonly stay near their oak tree food source. However, moving firewood can introduce this beetle into additional areas of California.
- Symptoms include thinning of the crown of the tree as the pest causes the crown of the tree to die.
- The insect was first linked to tree mortality in 2008 in San Diego County although it is likely that it was killing trees for several years before it was positively identified.
- GSOB aggressively attacks and kills large diameter coast live oak and California black oak. GSOB is currently the biggest insect threat to oaks in CA.
- The tree mortality is different from other pests. It’s not cyclical like the bark beetles. Nor is it the result of severe tree stress like drought.
So far, the pest has not been found in the San Bernardino National Forest, or outside a localized area in Idyllwild. The San Bernardino National Forest is trapping for the beetle and conducting surveys for injured trees.
For more information
The best website is
www.gsob.org which is put out by the University of California Cooperative Extension. Please report any suspicious activity to this website.
For firewood issues, please see www.firewood.ca.gov