What is the Polyphagous Shot Hole Borer (PSHB)?
The Polyphagous Shot Hole Borer (Euwallacea fornicatus) is one of the most devastating tree pests to invade South Africa. First identified in the KwaZulu-Natal Botanical Gardens in 2017, evidence suggests it may have been present since 2012.
This tiny beetle has now spread to 8 out of 9 provinces, with only Limpopo yet to report an infestation—likely due to a lack of awareness rather than absence. Originally from Southeast Asia, the PSHB has spread globally, affecting trees in the USA, Australia, Israel, and South Africa.
Why is the PSHB Such a Threat?
The PSHB infests over 200 tree species worldwide and more than 100 species in South Africa. It is estimated that if left unchecked, this beetle could cause economic damage exceeding R275 billion over the next decade. It poses a significant risk to fruit production and commercial forestry, threatening economic stability and food security.
How to Identify a PSHB Infestation
Identifying a PSHB infestation can be challenging due to the beetle’s small size (2mm). The female beetles, which spread the infestation, are winged and black, measuring between 1.8mm and 2.5mm. Males are smaller, brown, and wingless.
Signs of infestation include:
Shot-hole patterns (2-3mm holes in tree bark, often in clusters)
Wilting or dieback of branches
Sugary exudates or gummosis around entry holes
Frass (wood dust) at the base of the tree
Dark fungal stains on exposed wood
The Silent Killer: How the PSHB Damages Trees
While the beetle bores into trees, it is not the primary cause of tree death. The real damage comes from the Fusarium euwallacea fungus, which the beetle carries on its mouthparts. This fungus colonizes the tree's vascular system, disrupting water and nutrient transport. As a result, infested trees begin to wilt, lose branches, and eventually die.
The beetle spreads most actively when temperatures exceed 20°C, making South Africa's warm climate an ideal breeding ground. Additionally, its deep burrowing behavior makes it difficult to control with standard insecticides.
How PSHB Spreads
The PSHB spreads through:
Beetle flight (short distances)
Movement of infested wood (firewood, timber, mulch)
Trade and transport of infected plant material
What to Do if You Suspect a PSHB Infestation
If you suspect an infestation, follow these steps:
Take clear photos of the entire tree, including any dead or dying branches.
Identify the tree species (or take detailed photos of leaves, bark, flowers, or seeds).
Photograph signs of infestation such as shot holes, fungal stains, or sawdust frass.
Remove a small piece of bark with a chisel to check for fungal staining or tunnels.
Report the infestation to a professional arborist or tree health specialist immediately.
Current Control Methods: Is There a Solution?
1. Physical Removal & Destruction
In most cases, infected trees must be cut down and destroyed. The wood is then burned or solar-treated to kill the beetles and prevent further spread.
2. Chemical Treatments
Standard insecticides are ineffective since the beetle bores deep into the tree. However, research is ongoing into tree injections that deliver chemicals directly into the infested wood.
3. Biological Control
Beauveria bassiana: A fungus that attacks PSHB but has not yet proven to be highly effective.
Parasitic wasps and nematodes: Under investigation as potential natural predators of the beetle.
Preventing PSHB Infestations
To reduce the risk of infestation:
Avoid transporting firewood from unknown sources.
Inspect trees regularly for early signs of infestation.
Plant resistant tree species in affected areas.
Report any suspected infestations to tree health experts.
Frequently Asked Questions
1. Can PSHB kill my tree?
Yes. The beetle and its fungus can disrupt the tree's vascular system, leading to death if untreated.
2. How can I treat an infested tree?
Currently, the best method is removal and destruction. Consult a specialist before attempting chemical or biological treatments.
3. Is there a cure for PSHB?
There is no guaranteed cure yet, but ongoing research aims to develop effective treatments.
4. How does PSHB spread to new areas?
It spreads through beetle flight, movement of infested wood, and human transportation of infected plant materials.
5. Which trees are most at risk?
Indigenous and commercial trees, including avocado, maple, oak, and willow, are particularly vulnerable.
6. How do I report a PSHB infestation?
If you suspect an infestation, contact your nearest arborist or tree health specialist immediately.
Final Thoughts: The Importance of Awareness
The Polyphagous Shot Hole Borer is a serious environmental and economic threat to South Africa. Awareness and early detection are crucial in preventing its spread. If you own property with trees, regular inspection and responsible wood management can help protect your property and community.
For expert tree health assessments and PSHB management, contact Overberg Arborists, the leading tree care specialists in the Western Cape.
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Thanks for being a contributing member of our urban forest
The OA Team
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