Polyphagous shot hole borer is a tiny ambrosia beetle that inoculates a Fusarium fungus into the tree. The fungus disrupts water movement. The beetle’s larvae feed on the fungus. That pairing is Fusarium dieback, not goldspotted oak borer and not a eucalyptus longhorned borer.
UC Riverside’s Center for Invasive Species Research describes the beetle as about 0.1 inch long, smaller than a sesame seed. The exit hole is about 0.85 mm across. Females are dark. Males are smaller, wingless, and uncommon.
Branch Pro San Diego is a referral service. We connect you with licensed, insured independent local tree professionals. You hire and pay the professional directly. We don’t diagnose, treat, or remove trees.
Don’t peel bark. Don’t probe holes. Stay on the ground.
Which San Diego trees are hosts?
UCR lists known suitable hosts that show up in local yards and groves: avocado, California coast live oak, California sycamore, liquidambar (sweetgum), coral tree, box elder, castor bean, and others on that page. A Fallbrook Hass avocado and a Mission Valley sycamore are different settings. They can still share this beetle-fungus complex.
This page is the PSHB task. Oaks with D-shaped holes belong on the goldspotted oak borer guide. Eucalyptus galleries belong on eucalyptus dangers. Common tree pests does not cover PSHB.
If you have a coral tree, limb drop is a separate risk conversation: coral tree limb drop. If you have a sweetgum lifting a walk, that’s roots, not this beetle: sweetgum roots.
What does Fusarium dieback look like from the ground?
UCR describes white powdery exudate, dry or with wet bark stain, at a single beetle exit hole. The outer bark may look almost uninjured. Under that spot, the wood can be brown and necrotic from the fungus.
Many exit holes can appear on one trunk. One hole does not settle the pest. Staining has other causes, including irrigation against the bark and other borers.
Write down the species, the part of the tree that changed, and whether avocado fruit, a patio, or a play area sits under the canopy. A backyard Bacon avocado in Escondido is not a street sycamore in the City of San Diego. Ownership still has to be confirmed before anyone cuts.
What should you not do?
Don’t move firewood, logs, or green chips from a suspect tree to another neighborhood. Don’t inject a product because a neighbor did. Don’t assume a systemic pesticide is the default. Ask a qualified pest-control professional to identify the pest and choose any current labeled protocol.
Don’t treat every tiny hole as PSHB. Shot-hole symptoms on stone fruit leaves are a different problem. This beetle is in the wood.
If a line is involved, stay away and call 911 and SDG&E at 1-800-411-7343.
When is an on-site assessment the next step?
Call when you can see staining plus tiny round exits on a listed host, when the crown is thinning on one side, or when a target sits under dead wood. Tree health diagnosis and arborist consultation are how you request that visit.
If removal is proposed, tree removal is a separate scope. Avocado groves in north county have access and irrigation constraints that a city lot does not. See avocado pruning for the care side, which is not a PSHB treatment.
For paid tree work, look up the license on the CSLB license lookup. An active C-49 Tree and Palm license or an active legacy D-49 can both be valid. California’s current minor-work threshold is an aggregate price under $1,000, with extra conditions. If a pesticide application is proposed, that work can require its own license.
Frequently asked questions
Is polyphagous shot hole borer the same as goldspotted oak borer?
No. GSOB is Agrilus auroguttatus on oaks, with D-shaped exits. PSHB is a tiny ambrosia beetle with a round hole about 0.85 mm across and a Fusarium partner.
Can watering cure Fusarium dieback?
Irrigation is a site question. It is not a published cure for this beetle-fungus complex on UCR’s page. Identify the pest before anyone treats.
Should I chip the wood at home?
Don’t move or grind suspect wood until a professional handling plan is set. Confirm disposal rules for that address.
Can Branch Pro ID PSHB from a photo of a hole?
No. The independent professional inspects the tree. Tiny holes have more than one cause.
Get connected with a local pro
If the tree is on a conductor, use the utility steps first. For other PSHB questions bigger than a ground-level look, call (858) 400-4423. We’ll connect you with a licensed, insured independent local professional. Describe the host species, what you can see from the ground, and any target under the tree. You hire and pay that professional directly.