There is a current and real threat to most of the oaks in our community — the GSOB or the Goldspotted oak borer.
This beetle has killed tens of thousands of oaks in San Diego County, and has now been positively identified in Idyllwild. So far it has been found in three trees around the center of town and possibly a fourth.
Whether or not we can contain it will depend on how well we as a community, residents and agencies together, act to identify and remove infested trees.
The GSOB is not native to California, so it presents all the problems of an invasive pest — no natural predators, and limited host immunity.
It is native to southeast Arizona and points further south, and was mostly likely brought to San Diego in the 1990s in the form of firewood, which is almost certainly how it traveled here.
The mature beetle lays eggs on the bark surface and in crevices. After the eggs hatch into larval form, the larvae bore into the tree and grow underneath the bark, feeding on the tree and damaging its water and nutrient systems.
When the bug matures into a beetle, it exits the tree to find another host, leaving a small D-shaped exit hole when it emerges. Red staining is clearly evident under the bark, and sometimes on the external bark.
Unfortunately, we have no treatment as yet for an infected tree. Dr. Tom Coleman of the U.S. Forest Service, the foremost authority, is now conducting research on the effects of various insecticides, but the research is only in its middle stages and he cannot recommend any chemical to kill the beetle when it is identified in a live tree.
Like many public health threats, we must focus on prevention. No one should buy any oak that they are not certain is free of the GSOB. This means no oak from off the Hill, and no local oak unless someone knowledgeable assures you it is free of the beetle.
Burning infected wood will kill it, of course, but letting it lay outside in the warm months will allow it to mature and spread to oaks around your house.
The other public health action we must take is surveillance. There are certainly other infested oaks around town, and the sooner we can find them the sooner the tree can be removed, thus limiting the spread.
Everyone with oaks, especially black oaks, should pay close attention to their trees as spring approaches. The beetle likes large oaks, and will bore into the lower trunk, so anyone can check for staining or the D-shaped holes by looking at the lower part of the tree.
Our website, mcfsc.org, is loaded with lots of useful links for more information, or go to gsob.org or the Riverside County Fire website. Groups are working on this problem and more information should become available as they progress in their work.
Losing our oaks would drastically change the esthetics of the area. Many large black oaks are trees of great beauty and they are the most susceptible to the beetle. (It will also attack Canyon and Coast Live Oak.)
Please check your trees, especially as it warms, and if you suspect any are infected call the Nature Center at (951) 659-3850 to discuss your tree. Whatever you do, be extremely cautious about buying oak firewood, and avoid anything from off the Hill.
