PSHB: Critical information for growers this season

PSHB: Critical Information for Growers This Season

An update on detection, risks and best‑practice management

During the warmer temperature Polyphagous Shot‑Hole Borer (PSHB) activity increases. PSHB dispersal peaks January to March, making this the most important time of the year for surveillance and early intervention.

This article brings together the latest information growers need from recent workshops and field guidance to help protect orchard productivity and prevent further spread.

What Is PSHB and Why It Matters

PSHB (Euwallacea fornicatus) is a tiny ambrosia beetle that bores into live and dead wood, creating galleries where it cultivates a Fusarium fungus its food source. The fungus blocks the tree’s xylem, reducing water and nutrient transport, leading to dieback, limb failure, loss of productivity, and potentially tree death.

PSHB has a rapid reproductive cycle, short development time (30–40 days), and strongly female‑biased populations. A single female beetle can found a new colony, meaning one missed infestation can lead to repeated reinfestation across a block.

Which Orchard Crops Are at Risk?

The global host list for PSHB includes 500+ plant species, and many commercial fruit crops are known hosts.Reproductive orchard hosts (highest concern for spread)

  • Avocado

  • Apple

  • Mulberry

  • Fig

  • Pear (varies by species)
    These allow the beetle to complete breeding cycles and build population pressure.

Non‑reproductive hosts (still vulnerable)

  • Citrus (lemon, lime, grapefruit)

  • Carob

  • Grapevine

Where PSHB Thrives

Growers should prioritise surveillance in environments known to support PSHB:

  • Humid, shaded areas

  • Highly irrigated zones

  • Dense orchards with poor airflow

·       Freshwater systems, dam edges, drains, stormwater areas

·       Proximity within 150m to extremely susceptible hosts

 Reproductive extreme risk hosts (ornamental)

·       Robinia

·       Box elder maple

·       Coral or flame tree

 PSHB is consistently found in humid, shaded and high‑density host environments.

These conditions are common in modern orchard production, increasing both susceptibility and the risk of undetected spread. During the DPIRD eradication response, 90% of orchard trees found to be infected were within 150m of an extremely susceptible host as listed above. Consider any ornamental or windbreak varieties carefully.

 How to Detect PSHB in Orchards

Detection requires systematic scanning, starting from whole‑tree observations down to close‑up inspection.

1. Whole‑Tree Scan

Look for:

  • Canopy thinning or leaf discolouration

  • Dead or declining limbs (Fusarium dieback)

  • Fallen branches

  • Evidence of storm or mechanical damage

 2. Check Vulnerable Entry Points

Beetles preferentially target:

  • Branch collars

  • Natural cracks or fissures

  • Fresh splits, storm damage, snapped limbs

  • Pruning wounds, mower or machinery damage

 3. Close‑Up Symptoms

These are the most reliable indicators:

  • Entry holes ≈ 0.85–1 mm

  • “Frass noodles” or fine sawdust

  • Dark staining or lesions around entry points

  • Gumming or sap exudation

  • Sugar volcanoes (particularly on avocado)

 Heavy rain and wind can obscure symptoms such as frass and staining, making multiple symptom types valuable when confirming suspicion.

Storms Create Inspection Opportunities

Storm‑damaged branches frequently expose:

  • Blackened fungal galleries

  • Frass accumulations

  • Staining

Storm events should trigger immediate post‑storm orchard surveillance.

 High‑Risk Seasonal Window

PSHB trap capture data and temperature correlations show major dispersal events in warmer months, particularly January through to March.  This is the period when new infestations are most likely to appear.  Growers should increase inspection frequency during this window.

Preventing Spread: What Growers Must Avoid

The highest risk pathway for PSHB spread is movement of infested plant material, especially:

  • Unseasoned wood

  • Green waste

  • Mulch >2.5 cm

  • Firewood

Transporting waste off‑site can move beetles into new areas.

Correct Disposal

DPIRD recommends:

  • Chipping to <2.5 cm on site, don’t chip in mid-summer

  • Burying waste deeper than 30 cm and compacting

These methods prevent beetles from surviving in discarded material.

Grower Actions for Surveillance and Risk Reduction

Increase Surveillance:

  • Prioritise high‑risk hosts and humid zones

  • Schedule inspections around pruning and after storms

  • Monitor trees with signs of nutrient stress, pathogens, or bark damage

Manage Tree Health

Stressed trees are more vulnerable. Improve:

  • Water management

  • Soil aeration

  • Nutrient balance

  • Control of pathogens and trunk damage

Minimise Entry Points

  • Prune cleanly in dry weather

  • Disinfect tools (70% ethanol recommended)

  • Avoid unnecessary bark damage

Implement Waste Hygiene

  • Keep all green waste on the property where feasible

  • Follow QA movement restrictions

  • Ensure contractors understand the rules

What to Do if You Suspect PSHB

Identification of the beetle itself is difficult only molecular testing can confirm a specimen.
Growers should report symptoms, not beetles, using:

  • MyPestGuide Reporter app

  • DPIRD PaDIS hotline

If you find multiple symptoms, photograph the area and report immediately.

Staying Informed

The WA Agricultural Research Collaboration (WAARC) is investing in research to support growers in detection tools, modelling, lure development and host susceptibility studies.
For updates, visit dpird.wa.gov.au/pshb.

 References

·       Practical Tips for Detection of PSHB in Orchard Tree Species (DPIRD)

·       Grower Workshop 1 – Management, Surveillance & Risk Reduction (DPIRD)

Nardia Stacy