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Goldspotted Oak Borer Early Warning System: Help Us Monitor and Control a Beetle Killing our Native Oaks

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Goldspotted Oak Borer Early Warning System: Help Us Monitor and Control a Beetle Killing our Native Oaks

By Vincent Lazaneo

A new invasive insect, the Goldspotted oak borer (GSOB; Agrilus coxalis), is killing oaks in San Diego County and threatens the fate of oak trees in all of southern California. If we don’t take precautions now, this beetle may eliminate oaks from our landscape.

GSOB is capable of killing over 95 percent of susceptible oaks in a woodland in less than 10 years. It is responsible for tens of thousands of oak mortalities in San Diego County. Since 2002, GSOB has impacted the rural communities of Alpine, Descanso, Campo, Crest, Cuyamaca, Guatay, Jamul, Julian, Laguna, Lake Henshaw, Pine Valley, Santa Ysabel, and Ramona. It was also found in San Diego in Marian Bear Park.

We need your help to report new infestations.

With more than one million acres of oaks in southern California, it is nearly impossible for agencies to monitor all woodlands for signs of infestations. We are asking you to help us create an early warning detection system by monitoring oaks for GSOB damage.

Please contact Kathie Carter at kathiec@ucr.edu or call (951) 313-4193 to receive information about early warning monitoring. Carter is available to give informational presentations and training workshops to community groups interested in learning more about participating in the GSOB Early Warning System. Presentations can take place in a classroom or outdoor setting, and can be 15 minutes to one-hour long upon request.  We encourage you to participate in this program to help protect our native oaks.

Please visit the website, www.gsob.org, to learn more.

About GSOB

GSOB is native to Arizona, Mexico, and Guatemala, and was most likely brought here in the mid 1990s in firewood. The adult beetle (seldom seen) is about 1/4 inch long, with gold spots on its dark green iridescent back. It attacks mature coast live oak, canyon live oak, and California black oak. Larvae feed under the bark, starving the tree of nutrients and killing it within 1-3 years. Evidence of GSOB injury includes D-shaped exit holes (1/8 inch diameter), twig die-back, crown thinning, and staining and oozing of sap on the bark surface.

GSOB is easily transported long distances. Oak firewood brought from infested areas has a high probability of containing GSOB, and could devastate oaks around any location where the firewood is stored.

Currently, there are no known treatments to eradicate GSOB once it becomes established, and a GSOB outbreak is likely to kill many of the susceptible oaks in an area. This could cost a community millions of dollars for removal and restoration.

To stop this insect from spreading to other areas in southern California, purchase oak firewood locally and don’t move firewood.

Vincent Lazaneo is Urban Horticulture Advisor for UC Cooperative Extension.  He helped found the San Diego County Master Gardener Association more than two decades ago and serves as its advisor. He is the author of numerous articles on plants and pests that appeared in the San Diego Union-Tribune, California Garden and other publications.