Polyphagous Shot-Hole Borer Perth — What Tree Owners Must Know

Let me tell you something uncomfortable.

In June 2025, the people responsible for protecting Western Australia’s trees sat down and admitted they couldn’t win. After four years, $41 million, and the biggest surveillance program in DPIRD’s history — more than 1.75 million trees inspected across 60,000 properties — the National Management Group formally declared that eradicating the Polyphagous Shot-Hole Borer from WA was no longer technically feasible.

That’s not spin. That’s a government body telling you the truth.

The beetle won the eradication fight. Now the question is whether Perth’s trees — including its native ones — can survive the long game.

What You’re Actually Dealing With

The Polyphagous Shot-Hole Borer (Euwallacea fornicatus) is a beetle about the size of a sesame seed. It came from Southeast Asia — likely hitchhiking to Australia on untreated wooden articles or packaging materials, though nobody knows for certain. It turned up in a backyard maple tree in East Fremantle in August 2021, identified after the owner noticed their tree was dying and called in experts. Before arriving in WA, it had already spread to Israel, the USA, South Africa, and Argentina. It finds new countries the same way it probably found ours.

It now infests more than 30 local government areas across the Perth metropolitan area.

Here’s what makes it genuinely dangerous. The beetle doesn’t just eat your tree — it farms it. The female bores into a trunk or branch and cultivates a pathogenic fungus (Fusarium sp.) inside the tree as a food source for itself and its larvae. It’s the fungus that does the most damage: colonising the tree’s vascular tissue, blocking the movement of water and nutrients, and ultimately killing susceptible species. The beetle also creates physical tunnels — galleries — throughout the wood, adding structural damage to the vascular destruction. Some species can die within two years of infestation.

It’s a two-organism attack. And here’s the reason there’s no chemical solution: because the fungus destroys the vascular system, chemicals cannot be taken up and distributed through the tree. That’s not a gap in the current toolkit — it’s a fundamental biological problem. The only tools currently available are surveillance, movement restrictions, and removal or pruning of infested trees. That’s it.

There is currently no registered chemical treatment proven to eradicate or control PSHB. If someone is selling you one, ask to see the peer-reviewed evidence first.

You Are Legally Required to Report It

Most people don’t know this, so it’s worth stating plainly.

PSHB is a declared pest under the Biosecurity and Agriculture Management Act 2007 (BAM Act). Under section 26 of that Act — titled “Duty to report declared pest” — any person who finds or suspects the presence of PSHB must report it to DPIRD. Failure to report carries a penalty of up to $20,000.

The one qualification: if you know DPIRD has already received a report about the same tree or location, you’re not required to report it again. But if you’re the first to notice it, you have no choice in the matter — and that’s the right call. The surveillance network is the only early-warning system we have.

Quarantine Area Restrictions — and the Penalties for Breaking Them

A Quarantine Area (QA) covering the entire Perth metropolitan area is in place, monitored by approximately 3,000 sticky traps across the city. The QA is divided into two zones:

The Management Zone — the inner metro area where infestations are known.
The Containment Zone — the buffer between the Management Zone and the outer QA boundary.

You cannot move host plant material from the Management Zone to the Containment Zone, or from anywhere inside the QA to outside it. This applies to unseasoned wood, green waste, and mulch larger than 2.5cm in diameter, and live plants with woody stems greater than 2cm in diameter. Machinery used for mulching or chipping must be cleaned of all wood and plant material before crossing zone boundaries.

Breaching these movement restrictions is an offence under the BAM Act, carrying penalties up to $20,000. These are not guidelines — they are enforceable legal obligations.

The 2.5cm diameter threshold exists for a specific reason: chipping infested material to below that size kills the beetle. That’s why all trees removed under DPIRD authorisation are chipped on-site. Moving unchipped wood potentially moves a live colony.

PSHB doesn’t travel far on its own — but it travels very well when people move infested wood. Firewood is a particular risk. Buy it where you burn it, and never bring Perth firewood into regional areas.

Check DPIRD’s interactive map online to confirm which zone your property sits in before your next garden clean-up, green waste removal, or tree work.

Which Trees Are at Risk

The global host list runs to over 500 species. In WA, PSHB has already been confirmed in more than 200.

The key distinction is between reproductive hosts — trees where the beetle and fungus can successfully breed and multiply, acting as population amplifiers — and non-reproductive hosts, where the beetle can attack but can’t complete its lifecycle, so trees generally survive.

The worst reproductive hosts are introduced species. Box elder maple (Acer negundo) is the highest-risk tree on the planet for this pest and has been the primary amplifier of PSHB across Perth. Coral trees (Erythrina x sykesii), robinia, willows, plane trees, oaks, avocado, and castor oil plant are also high on the list. If you have any of these on your property inside the QA, they deserve your immediate attention — and serious consideration of whether they should be replaced.

Among Australian natives, the picture is more nuanced — but not clean. River sheoak, Moreton Bay fig, Port Jackson fig, and wedding bush carry very high susceptibility ratings. Among WA natives specifically, swamp paperbark (Melaleuca rhaphiophylla), sea hibiscus, and cottonwood are rated very high risk. Casuarina, marri, red flowering gum, and certain banksias and paperbarks sit in the high susceptibility category.

Here’s the critical context: in WA, the overwhelming majority of infested native trees have been found growing next to heavily infested preferred hosts — particularly box elder maple. The beetle is not hunting your natives as a primary target. It’s spilling over from the trees it actually wants. Remove or manage the high-risk introduced species nearby, and your natives are significantly safer. That’s not a reason to be complacent — it’s a reason to understand where the real risk is actually coming from.

The WA host list is updated monthly. Always check the current version at DPIRD’s website before making planting decisions.

What PSHB Has Already Cost Perth

Kings Park is the clearest example of what this pest does when it gets into a significant tree collection.

Established Moreton Bay Figs were lost from the Mounts Bay Gardens section of Kings Park. The response team collected seed locally, grew nearly 18,000 replacement plants, and uncapped a natural spring on site as part of the restoration process. That’s not a minor setback — that’s years of work and irreplaceable mature canopy gone, with a decade-long recovery underway.

Across Perth, DPIRD has removed more than 2,600 trees from residential properties alone under its authorisation program. The WA Government has allocated $7.2 million to the Tree Recovery Program — including grants to local governments to plant three replacement trees for every one lost to PSHB, and residential rebates of up to $150 per tree removed under DPIRD authorisation.

Lost trees don’t come back. Replacement plantings take decades to reach maturity. That gap is the real cost.

What the Beetle Looks Like in Your Tree

You almost certainly won’t see the beetle itself. What you’ll see is what it leaves behind.

On the trunk, stems, and branches:

Tiny circular entry holes roughly 1–2mm across — about the size of a ballpoint pen tip
Powdery sawdust (frass) around or below those holes, sometimes formed into small “noodles” pushed out from the entry point
Dark gummy staining oozing from bore holes — sometimes the resin pressure physically pushes the beetle out
Discolouration or staining of bark around entry points

In the canopy:

Wilting or yellowing leaves, often starting at the top
Branch dieback
In advanced cases, structural branch failure — infested trees become genuine safety hazards

Spring and autumn are when the beetle is most active, dispersing to new host trees. A female can fly up to 400 metres. One heavily infested box elder maple is effectively a source population for the surrounding block.

DPIRD has published a short animation on YouTube that walks through the visual signs clearly. Search “PSHB WA DPIRD” to find it.

What to Do

If you see suspicious bore holes or symptoms on a tree, don’t move anything. Don’t prune it and take the branches elsewhere. Don’t mulch it. Don’t load the material in a trailer. Leave it exactly where it is and report it.

When a tree is confirmed as infested, removal is not always the immediate response. Where possible, affected stems and branches are pruned first, with pesticides applied in some cases to limit the borer. Full tree removal is the last resort — but when it’s necessary, all material is chipped on-site to below 2.5cm before it moves anywhere.

Report via the MyPestGuide® Reporter app — free on iOS and Android. Photograph the bore holes with a ballpoint pen or ruler in the frame so DPIRD can assess size. Make sure location services are enabled on your phone when photographing. Submit the report. It goes directly into the national surveillance network.

Call PaDIS on (08) 9368 3080 for identification help and direct advice from DPIRD’s Pest and Disease Information Service.

Email: padis@dpird.wa.gov.au

Reporting is a legal requirement. The penalty for failing to report a declared pest is up to $20,000.

The Honest Summary

This pest is now permanently in Perth. It can’t be eradicated. The response has shifted to slowing its spread and building long-term management capacity — which is the right call given the facts, even if it’s a hard one to accept.

What you can do is clear: know your zone, follow the movement restrictions, learn the signs, report anything suspicious, consider replacing high-risk introduced trees, and choose species carefully when planting. None of that is complicated. All of it matters.

The trees that come down to this beetle are gone. The ones that don’t get planted because nobody was paying attention are also gone. Both of those outcomes are avoidable with a little knowledge and a little care.

If you’re choosing new trees for your Perth garden, read our guide to the Top 10 Native Trees for Perth Backyards and our Top 10 Native Trees for Small Perth Backyards — both include PSHB risk ratings for every tree recommended.”

Resources from DPIRD

This article draws on publicly available information from DPIRD, the Biosecurity and Agriculture Management Act 2007, the WA Auditor General’s Office, Gardening Australia, and the national outbreak.gov.au response portal. It reflects the status of the PSHB response as of 2025. The WA host list is updated monthly — always check the current version before making planting decisions.

Legal disclaimer: This article is for general information purposes only. It does not constitute legal advice. Laws, regulations, and quarantine conditions can change — always check current requirements directly with DPIRD before acting. For obligations specific to your property or situation, consult DPIRD or a qualified legal professional.