Tracking the Shot Hole Borer: Lessons from the IPM TAG Collaborative
Two years of monitoring the invasive shot hole borer across the South Bay have taught us where the pest spreads fastest, which trees are most vulnerable, and why regional coordination is the only effective response.
Kyle D. Peczkowski
Board Certified Master Arborist & Urban Forester
The invasive shot hole borer is a small beetle with a large impact. It carries Fusarium fungi into the vascular systems of susceptible trees, causing branch dieback, canopy thinning, and eventually death. In Santa Clara County, the most vulnerable species are coast live oak, sycamore, and willow.
When we first detected the pest in 2023, the response was fragmented. Individual cities treated trees on their own property, but the beetle did not care about jurisdiction. Infested trees on private land became reservoirs, reinfecting adjacent public trees after treatment.
The IPM Collaborative changed the math. We standardized trap placement, agreed on a common identification threshold, and shared a regional map of confirmed detections. For the first time, we could see the outbreak as a pattern rather than a series of unrelated incidents.
The data has been humbling. The pest spreads fastest along riparian corridors and in landscapes with high irrigation stress. It is also strongly associated with wood movement — firewood, green waste, and untreated chips. That means sanitation and public outreach are as important as insecticide.
We are not going to eradicate the shot hole borer. The goal is to slow it down, protect the highest-value trees, and buy time while researchers develop better tools. That only works if we keep sharing what we learn.