INVASIVE PEST THREATENS SAN DIEGO COUNTY

By Kate Yapjoco

May 21, 2012 (San Diego) – The goldspotted oak borer (GSOB) is threatening the oak trees of San Diego County.  Widespread oak tree mortality can have severe environmental and human safety implications.  The dead and dying oak trees create a more dangerous wildfire situation by adding combustible fuel and hazards along evacuation routes.

According to Jeff Stoffel, Vegetation Manager for the County of San Diego, the GSOB was first detected in San Diego County in 2004 during a trap survey for invasive tree pests.  In 2008 it was linked to elevated levels of oak mortality ongoing in San Diego County since 2002. The borer is native to Arizona and Mexico and was likely introduced into southern CA via infested oak firewood. 

Stoffel indicated that currently, the largest populations of oak trees in the county are in the east and north east portions but the potential for the invasive pest to spread far and wide through firewood movement is high.

The oaks impacted by the borer are coast live oaks, canyon live oaks and California black oak.  Once the GSOB bores into the bark of the tree it lays larvae which then create feeding galleries underneath the surface of the bark.  Evidence that a tree has been impacted is:

·         Red or black staining in dime-sized to half foot sections

·         Blistering and oozing on the surface of the tree

·         Crown thinning

·         Twig and branch die-back

·         Premature leaf loss

Under a collaborative program, agencies and organizations are working together to determine the distribution, impact and possible prevention methods of tree mortality caused by GSOB.  They are calling on the public to help in detecting the pest in oaks and reporting it.  Sightings can be reported here.

For more information about the Goldspotted Oak Borer please visit http://ucanr.org/sites/gsobinfo/.