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Concern as tree-killing beetle spotted in southern suburbs

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A tell-tale sign of the invasive shot hole borer (ISHB) infestation. Issues like ISHB has brought the need for self-regulation in the tree care industry to a tipping point, the Cape Arboriculture Association believes.
A tell-tale sign of the invasive shot hole borer (ISHB) infestation. Issues like ISHB has brought the need for self-regulation in the tree care industry to a tipping point, the Cape Arboriculture Association believes.

An invasive beetle that has been sowing carnage among trees in Somerset West has been discovered in both Newlands and Rondebosch.

Eddie Andrews, the City of Cape Town’s deputy mayor and Mayco member for spatial planning and environment, this week confirmed that two trees (a Boxelder) infested with the invasive Polyphagous Shot Hole Borer beetle (PSHB) were discovered on a private property off Kildare Road in Newlands on Tuesday 24 January.

According to Paul Barker, a consulting arborist with extensive experience in managing PSHB, a report of a secondary PSHB infestation has since been confirmed at a site off Main Road in Rondebosch.

Hailing from South East Asia, the invasive ambrosia beetle was first discovered in KwaZulu-Natal in 2017.

It quickly spread to another seven of South Africa’s nine provinces with Limpopo being the only exception.

In the Western Cape, the outbreak was confined to the Garden Route and Somerset West – that is until now.

“We are extremely concerned about this latest sighting in Newlands as to date we have managed to contain the invasive Asian borer beetle to the Somerset West area with the assistance and cooperation of residents,” says Andrews.

Barker says the Boxelder trees found in Newlands were severely infested with PSHB.

“More than 200 beetle entry and exit holes were visible on the trees, making them an amplifier of PSHB pressure on surrounding trees.”

PSHB is a tiny black beetle (2 mm in size) that, in symbiosis with a fungus called Fusarium euwallaceae, aggressively kills trees.

A paper conservatively estimates the mortality rate of trees (growing in a city, town or suburb) infested with PSHB at 25%.

While research is ongoing to find a method that will be effective in eradicating this pest without harming the surrounding environment, the use of pesticides and fungicides has a limited effect.

The City states that while these may reduce the rate of recolonisation in lightly infected trees, these methods have not proven effective at eradicating PSHB from infected trees.

According to the management protocol drawn up by the City’s Invasive Species Unit, the priority is the swift identification and removal of highly infested trees to reduce the beetle population.

The protocol requires that the wood from an infected tree be chipped on site and carefully removed under cover of heavy-duty plastic and incinerated at an appropriate site.

Barker states that, under the supervision of the City, the two identified infested Boxelders have since been felled and chipped by a local arborist.

“The PSHB-infested green waste generated by the felling operation was safely disposed of by a City of Cape Town service provider equipped to handle infested material.”

Andrews encourages residents in the Newlands and Rondebosch areas to inspect the trees on their properties for possible beetle infestations, in particular Boxelders.

“Sightings must be reported to the City as soon as possible so that we can prevent the spreading. Working together we can contain this beetle,” he says.

More information is available on the City’s website, as well as a form to report sightings.

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