City keeping track of the Shot Hole Borer Beetle in Somerset West
14 December 2020
Since the infestation of the Polyphagous Shot Hole Borer Beetle (PSHB) in Somerset West was confirmed in April 2019, the City of Cape Town’s Invasive Species Unit has prioritised the monitoring and surveying of the PSHB for the entire Somerset West area to identify all reproductive and non-reproductive host trees and inspect them for PSHB presence. Through this extensive survey the top five most infested reproductive host trees in the area have been identified and data has confirmed that PSHB is currently confined within the Somerset West area.
Although our data has confirmed that PSHB is currently confined within the Somerset West area, the City is still conducting additional PSHB presence surveys in other parts of the city where these top five trees are found for early detection purposes. The Invasive Species Unit (ISU) is continuing to work closely with the Stellenbosch University’s Department of Conservation Ecology and Entomology in PSHB monitoring.
The City is prioritising the containment of the PSHB infestation in Somerset West as there is currently no chemical or biological control methods available to control PSHB and Fusarium fungus that is carried by this beetle. This is done by removing heavily infested trees, mostly reproductive host trees.
‘We have identified that the movement of firewood is one of the major contributors to the spread of PSHB in other parts of the country. This is a big concern for us, particularly with the upcoming festive season. We urge residents to please avoid the unnecessary movement of firewood particularly to natural environments. Firewood traders must please check and inspect their firewood for any PSHB symptoms too. The protection of our natural environment and precious urban forest lies in our hands, let us all play our part in preventing the PSHB spread in the city and continue to report infestation via the ISU online reporting tool,’ said the City’s Mayoral Committee Member for Spatial Planning and Environment, Alderman Marian Nieuwoudt.
This online reporting tool allows members of the public to report any possible and potential PSHB infestations within Cape Town and enables the City to assess all reported possible infestations much faster.
The ISU also developed and published a PSHB Management Protocol this year which outlines management actions to be considered by the City once PSHB presence is confirmed. Furthermore, the protocol provides important information to assist the public with the identification of PSHB infested trees and reporting of any potential PSHB infested trees to the ISU.
The City is encouraging residents to report any suspected sightings of a PSHB invasion on https://www.capetowninvasives.org.za/shot-hole-borer. Once reported, officials from the Invasive Species Unit and an arborist at the City Parks and Recreation Department will conduct an investigation. The website has an extensive database of information about PSHB where residents can learn more about this destructive beetle.
More about the PSHB beetle
The beetle is the size of a sesame seed and is approximately two millimetres in length. Its symbiont fungal partner are threatened trees across South Africa
It is an ambrosia beetle native to Southeast Asia
It was first discovered in South Africa in 2017 on London plane trees in KwaZulu-Natal’s National Botanical Gardens in Pietermaritzburg
The beetle is invading and poses a threat to exotic and indigenous trees across South Africa
The beetle’s most likely pathway or vector is through the movement of infested wood, originating from dead or dying PSHB infested trees, including wood intended to be used for cooking or heating
Lifecycle of the PSHB beetle
The female beetle carries with her three species of fungi, including the pathogen, Fusarium euwallaceae
The adult females burrow into trees to establish brood galleries where they lay their eggs. They introduce the fungus which colonises gallery walls, becoming a food source for developing larvae and adult beetles. The fungus kills the water conducting tissues of the tree and can lead to branch dieback and eventually causes the tree to die
What trees are invaded?
Alien trees infested to date include London plane trees, sweetgums, Japanese maples, Chinese maples, pin oaks, and English oaks
Indigenous trees invaded to date include the coast coral tree, the forest bush willow and the Cape willow
What to do
Burning of the infected wood is the preferred method
Chipping of the wood into small pieces for compost is also recommended as the heat build-up in the composting process will kill the beetle
Once the tree has been felled the debris should be cleared as soon as possible and if required, the area should be sanitised
Infested plant material can be placed in refuse bags and sealed. The bags must be put in direct sunlight for solarisation as the heat from the sun helps to kill the beetle and its larvae
End
Published by:
City of Cape Town, Media Office
