Polyphagous Shot Hole Borer

Polyphagous shot-hole borer (PSHB), a wood-boring exotic beetle which has been gradually spreading across the Perth metropolitan area since August 2021, was first detected in a street tree in the Town of Cambridge in February 2023.

Trees in Floreat, West Leederville, Wembley, Lake Monger and Wembley Golf Course have since been detected to have PSHB.

The Town anticipates a general increase to PSHB spread rate, and an increase in secondary infections in line with global trends, as pest numbers increase and tree health declines due to persistent pest pressure.

The Town is working closely with the Department of Primary Industries and Regional Development (DPIRD) to monitor and respond to the situation. Where trees are infected, DPIRD will be implementing prescribed treatments, which can include pruning of the tree or its full removal.

In the event that a tree has to be removed, the Town will endeavour to replace it with an alternative tree species as soon as reasonably practicable.

Mayor Gary Mack said: “The Town has a dedicated team who manage our Urban Forest, and we are actively managing the spread of PSHB across our suburbs through early intervention. We cannot accurately predict how many more trees will be infected, but the range of highly vulnerable species is limited. For now, we’d encourage our residents to help monitor for PSHB, as early detection is key to minimising further impact on neighbouring trees.”

There are a number of symptoms that indicate a tree may be infested, including:

• Beetle entry holes (approximately the size of a ballpoint pen tip or sesame seed);
• Discolouration or staining of wood;
• ‘Gumming’; the appearance of thick resin or sap;
• ‘Galleries’; intricate tunnels or galleries where PSHB farm fungus;
• Frass; or sawdust that can be present extruding from trees, produced by the beetle’s tunnelling; and
• Dieback.

Reproductive hosts and important trees to check are Maple, Plane, Coral tree, Robinia, Poinciana, Fig, Mulberry, Willow and Avocado.

Breeding and Spreading

• A single female can start a new infestation.

• Adult females can fly up to 400 m, but typically attack hosts within a range of 35 m.
• Perth’s climate supports year-round reproduction. When temperatures exceed 27 °C for extended periods (e.g., 197 days), the beetle can complete its lifecycle in under 30 days, allowing for 4–5 generations annually.
• Detection is difficult at low population densities and before reproduction begins.
• Moving infested wood or plant material is the main way PSHB spreads.
• PSHB can survive up to five months in cut timber and branches.

Treatment Options

UWA, Curtin, and Murdoch Universities are trialling various treatments, including:

• Injecting resin into the heartwood of trees to stop the development of the fungus PSHB feeds on.
• Using pheromone traps near affected trees to lure beetles out.
• Applying AI multispectral aerial imagery to monitor tree health.
• Combining multiple treatment methods.

Further reading is available through the WAARC PSHB Research Program.

Additional trials include:

• Surface Sprays: These use insecticides and/or fungicides. Only the most toxic chemicals produce high mortality rates, and they do not penetrate bark or wood.
• Systemic Trunk Injections: These move through the tree’s internal system, reaching sapwood, leaves, flowers, and fruit. However, they are costly, slow to apply, and may cause unintended damage.

Residents who suspect they have borer damage to trees should call the DPIRD’s Pest and Disease Information Service on (08)9368 3080, reported via the MyPestGuide® Reporter app, or email padis@dpird.wa.gov.au.

Further information on the beetle can be found at www.agric.wa.gov.au/borer.

 

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