Pictured: The team from Los Angeles County at a Goldspotted Oak Borer tabling event. Photo courtesy of MIG, Inc. and County of Los Angeles.

California’s oak trees are under siege. The Goldspotted Oak Borer (GSOB), an invasive beetle species, has caused the death of tens of thousands of oak trees across Southern California, threatening not only ecosystems but also the cultural and economic vitality tied to these iconic trees. Addressing this crisis requires coordinated community action, education, and policy-driven interventions.

The Threat of GSOB

Native to Arizona and northern Mexico, GSOB (Agrilus auroguttatus) was first detected in California in 2004 in San Diego County. Likely introduced through infested firewood, the beetle has since expanded its range. By 2008, it was linked to widespread oak mortality, particularly among coast live oak (Quercus agrifolia), canyon live oak (Quercus chrysolepis), and California black oak (Quercus kelloggii). These tree species form the backbone of Southern California’s ecosystems, providing critical habitat for wildlife, supporting water retention in arid climates, and enhancing community aesthetics and shade.

The lifecycle of GSOB is particularly insidious. Adult beetles lay eggs in the crevices of oak bark, and the larvae burrow into the cambium layer, disrupting the tree’s ability to transport water and nutrients. Signs of infestation include crown thinning, bark staining, increased woodpecker activity, and the presence of D-shaped exit holes where adult beetles emerge.

Pictured: A palm card with information on the Goldspotted Oak Borer. Courtesy of County of Los Angeles.

The ecological impacts of GSOB infestations extend far beyond the loss of individual trees. Oak woodlands are biodiversity hotspots, supporting a wide array of plant and animal species. The death of mature oaks leads to habitat loss, increased soil erosion, and reduced carbon sequestration capacity. Dead and dying trees also elevate fire risks, a particularly dangerous consequence in wildfire-prone regions.

Communities bear the economic burden as well. Removing dead oaks is costly, especially for public agencies and homeowners. Additionally, the loss of trees diminishes the recreational value of parks, trails, and open spaces. Many Californians hold personal and cultural connections to oak trees, making their loss deeply felt on an emotional level.

Mobilizing Against GSOB

The fight against GSOB requires a multi-pronged approach that includes public education, community engagement, and proactive management strategies.

• Public Education and Outreach: Many Californians remain unaware of GSOB and its devastating impact. Educating communities about the importance of early detection and prevention is critical. Community workshops and public service campaigns can teach residents to identify GSOB symptoms and report infestations. In coordination and collaboration with various departments at the County of Los Angeles, the Chief Sustainability Office has undertaken a robust education and outreach initiative to prevent the spread of this invasive pest and protect oak trees.

  Specifically, L.A. County has conducted well-attended public workshops in which residents, landowners, and other local stakeholders learned to identify GSOB infestations, report sightings, and implement best practices to protect oak trees. The County has also shared information at community events, such as farmer’s markets, reaching a broader audience. Additionally, L.A. County has hosted a Community Stewards Training Workshop and developed an associated toolkit to empower organizations and individuals, such as docents and volunteers, with the knowledge and tools needed to train and inform others within their networks about GSOB. This train-the-trainer approach ensures the broader dissemination of critical information, multiplying the impact of the County’s outreach and fostering a community-wide commitment to protecting oak trees.

Pictured Left: A community workshop in Los Angeles County to provide information on GSOB. Photo courtesy of MIG, Inc. and County of Los Angeles.

Pictured Below: A GSOB both at a local farmers market in Los Angeles County. Photo courtesy of MIG, Inc. and County of Los Angeles.

• Monitoring and Reporting: Surveying and monitoring efforts led by staff from public agencies and trained volunteers can help detect GSOB and track its spread. Suspected GSOB should be reported through the “Goldspotted Oak Borer Symptoms Reporting Form” on gsob.org. The reporting tool is actively monitored, and GSOB experts in the relevant county are promptly notified to evaluate whether a potential new infestation has occurred.

• Proactive Tree Management: Consulting with certified arborists to assess tree health and determine treatment options can protect critical oak populations. A topical insecticide applied by a certified pesticide professional to the main stem and to the larger branches (greater than eight inches in diameter) can prevent GSOB injury to high-value oaks. Applications near water bodies or sensitive habitats should be avoided to comply with environmental guidelines and prevent unintended contamination. Additionally, strategic removal of severely infested trees can slow GSOB’s spread.

Role of Park and Recreation Agencies

As stewards of public lands, parks and recreation professionals are critical in the fight against GSOB. Parks often serve as the front line in identifying and managing infestations. Incorporating GSOB prevention and management into park maintenance plans ensures that staff are equipped with the knowledge and resources needed to respond effectively. Park agencies may also plant oak tree saplings at parks where appropriate as young oaks are less susceptible to GSOB.

Furthermore, parks can serve as educational hubs. Hosting workshops, creating interpretive signage about oak trees and GSOB, and partnering with schools for field trips can raise public awareness and foster community involvement. The National Recreation and Park Association (NRPA) and its member agencies have long promoted the value of parks as spaces for education and environmental stewardship—this is an opportunity to amplify that role.

Partnerships for Success

Coordination and collaboration are key to combating GSOB. Public agencies, non-profits, academic institutions, and local communities must keep each other updated and work together to pool resources and expertise. Organizations like the University of California Cooperative Extension – Agriculture and Natural Resources (UCANR) and the California Department of Forestry and Fire Protection (CAL FIRE) provide invaluable resources for education and management.

Looking Ahead

The GSOB crisis is a stark reminder of the challenges posed by invasive species in an increasingly interconnected world. Yet, it also presents an opportunity to strengthen our commitment to environmental stewardship. By mobilizing against GSOB and protecting oak trees, we preserve not only an ecological legacy but also the cultural and recreational benefits that make California and many of its parks so special.

Resources:

• For more information and resources about GSOB, please visit gsob.org.
• For more information about L.A. County’s efforts to protect oak trees from GSOB, please visit this site.

Clement Lau, DPPD, FAICP, is a Senior Analyst with the Los Angeles County Chief Sustainability Office where he works on a variety of tree-related initiatives to support implementation of the County’s Community Forest Management Plan.