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Our Burning Planet

Cape Town battles to save urban forests from tree-killing Vietnamese beetles

Cape Town battles to save urban forests from tree-killing Vietnamese beetles
A wood chipper processes infected branches, breaking them down to minimize the risk of beetle survival. (Photo: Kristin Engel)
Kristin Engel
By Kristin Engel
4 Apr 2025
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South Africa is facing an escalating ecological crisis – a tiny invasive beetle from Vietnam is killing off trees in urban and natural forests. More than 7,000 trees have been affected by the tree-killing beetle in Cape Town alone.

Since its discovery in KwaZulu-Natal in 2017, the polyphagous shot hole borer (PSHB) has been confirmed in eight of South Africa’s nine provinces — Limpopo being the only exception. In Cape Town, the infestation has been severe, with more than 7,000 trees confirmed to have been infected.

The PSHB infestation in South Africa was first seen affecting crops such as pecan and macadamia orchards, and then moved to commercial forestry species.

female borer beetle A female polyphagous shot hole borer (PSHB) beetle. (Photo: S Bush / Fabi)



polyphagous shot hole borer map Polyphagous shot hole borer map of distribution in South Africa. (Photo-FABI)



But now, one of the biggest risks from the infestation is in urban forests, on streets, parks and garden trees, with thousands lost to the tiny beetle as researchers, communities and municipalities battle to contain the spread.

The most unpredictable impact has been on natural/native forests, where a pattern has developed with the beetle moving from urban trees to indigenous forests.

A research study by Garyn Townsend, Martin Hill, Brett Hurley and Francois Roets published in February 2025 found that PSHB was affecting nearly all major South African forest types, except mangrove forests, as they are dominated by unsuitable host species. 

They found that over five years, PSHB invaded all but one forest type with the PSHB “colonisation” recorded on numerous native tree species, often resulting in severe infestations and sometimes mortality. 

infestation signs The telltale signs of PSHB infestation. This is the point of entry of the PSHB on a London plane tree in Dam Park, Strand on 2 April 2025. (Photo: Kristin Engel)



response management With no known cure for the polyphagous shot hole borer, rapid response and responsible management remain the best tools to slow its devastating impact on trees. (Photo: Kristin Engel).



“Many tree species and families had higher than expected infestation rates. An increase in PSHB-attacked trees and infestation severity was observed over the course of the study, with trees having a 7.5% increased chance of PSHB infestations per year and PSHB holes increasing by over 10% annually,” said the study.

With no known cure or effective eradication method, municipalities have been scrambling to respond. The beetle infestation has increasingly spread, with insufficient legislation on how to manage it since it was first confirmed in the country in 2017.

Read more: Tiny but seemingly invincible beetle has killed thousands of trees across SA, millions more at risk

In the City of Cape Town, the approach focuses on containment, mitigation and public education coordinated through its Invasive Species Unit, taking lessons from how other South African communities have responded, as well as California, Israel and more recently Perth.

City of Cape Town’s PSHB approach


Mashudu Phalanndwa is the project lead for PSHB response and head of green jobs in the City of Cape Town’s Invasive Species Unit – part of his role is to coordinate the management of invasive species across Cape Town.

In an interview with Daily Maverick, Phalanndwa said their response to the PSHB infestation was to actively monitor and report, with intensified inspections to track the spread.

To date, Phalanndwa said, they had identified more than 7,000 trees affected by PSHB since 2019 when it was confirmed in Cape Town, but that the number was higher than what had been identified.

This was because identified trees were only those to which the city had access. These were either on public land, streets, road verges or on private properties to which the owners had given the city permission to enter.

chainsaw weeping willow A chainsaw operator from the City of Cape Town’s Invasive Species Unit assesses the extent of polyphagous shot hole borer damage on a 20-year-old weeping willow before it is cut down at Dam Park in Strand on 2 April 2025. (Photo: Kristin Engel)



Chainsaw operators from the City of Cape Town’s Invasive Species Unit at Dam Park, Strand. (Photo: Kristin Engel)



infected logs Infected logs to be fed into a wood chipper and loaded on a truck for transport to a disposal site, preventing the accidental spread of the beetle. (Photo: Kristin Engel)



wood chipper A wood chipper processes infected branches, breaking them down to minimise the risk of beetle survival. (Photo: Kristin Engel)



According to Phalanndwa, based on observations from a distance, many private properties that the city did not have access to were home to reproductive host trees and showing symptoms of infection.

“So the number could be quite a bit higher than what we have on our records currently. The impact that we are seeing on the tree canopy is quite high,” said Phalanndwa.

They have been conducting visual surveys that entailed assessing all the street trees in the city of Cape Town, with a focus on the areas with confirmed PSHB infestations.

“We’ve got people on the ground that are conducting those mass surveys to ascertain the extent of spread in those particular areas. But what we’ve also been doing is we’ve been working very closely with residents wherein they would inform us when they suspect a tree or trees, either on the streets or in their properties, are affected by PSHB or are showing that there are PSHB symptoms,” said Phalanndwa.

The Invasive Species Unit would then visit or dispatch a team of quality controllers who would inspect the trees. 

Phalanndwa said that because some of the host trees, such as box elders (Acer negundo), are good indicator species of early invasion, they monitor some box elder trees outside areas of known PSHB infestations.

“That way we will be able to pick up an early invasion should it move to those areas in the city where we know it’s not [yet] affected by PSHP,” said Phalanndwa.

The city is also implementing training to educate anybody, whether they own a tree or handle tree material, to identify whether the material is infested with PSHB. If infested, people can learn how to properly handle and move that material if needed, minimising the risk of spread.

Luke Potgieter, invasive species and PSHB researcher for the City of Cape Town, also affiliated to Stellenbosch University, said they were planning on rolling out mass trapping across the city using bottle traps, used to determine whether PSHB is in an area. 

“These traps will be largely set out in areas along the leading edge of infestation. That’s really where we can track and have a better understanding of the current distribution of the beetle and where it’s likely to progress,” said Potgieter.

They would set up the traps in more isolated areas that may or may not be at risk of PSHB infestation, such as landfill sites and green waste facilities, particularly if those were close to known reproductive host trees. 

“Those trees can harbour the beetle and those traps will likely be set out in the coming spring when the weather permits and when the increased temperatures increase the beetle activity,” said Potgieter.

Challenges in dealing with PSHB 


Phalanndwa said one of the most concerning challenges was insufficient legislation.

“For as long as we don’t have enforcement tools in place, all the trees that we have — especially on the streets, in the public open spaces and any land that belongs to the City of Cape Town — still remain at risk from the invasion that could come from neighbouring properties, municipalities and other areas,” he said.

Another challenge was that they needed better management coordination between government entities at local, provincial and national government levels. 

“This invasion is becoming a global invasion, and it’s something that the city on its own cannot manage without better coordination,” said Phalanndwa.

The city has recently been in talks with the Western Cape Department of Environmental Affairs and Development Planning to look more intensely into how they could better coordinate the management of PSHB. 

They are also in contact with neighbouring municipalities. Phalanndwa said. “We’re starting to see more and more of our neighbours wanting to put in effort and reaching out for help for training and assistance with the management protocols and procedures that the city has put in place.” 

But he said this was still a risk until they could have something solid in terms of coordination, working together to manage the infestation.

The biggest challenge, according to the Department of Forestry, Fisheries and the Environment (DFFE) and the city, was the movement of infested material, specifically managing the movement of firewood — this was now the biggest driver of the spread of the beetle. 

“It’s difficult to manage the movement of firewood because the industry itself is not regulated,” said Phalanndwa.

This meant they had to rely more on the attitudes of those involved in the firewood industry, and their knowledge of the impact and the role that they could play in managing the movement of firewood or trying to mitigate the risk factor for the spread of PSHB.

Peter Mbelengwa, DFFE chief director of communication and advocacy, said that due to budget cuts through Treasury’s cost-containment measures, the department could not continue funding the monitoring and research component of the PSHB strategic plan. But the department had provided funds to update the plan to make it more inclusive and allocate responsibilities to provincial and local governments.

According to the department, there was a lack of funding to do the diagnostics and identification of the PSHB, and there was limited ability to capture and run a single database for all PSHB in the country that would be accessible to anyone for information purposes. 

Phalanndwa said it would be a great help if PSHB were listed as an invasive species under the National Environmental Management: Biodiversity Act (Nemba).

In response, the DFFE told Daily Maverick it was in the process of listing the PSHB on the proposed list to be published for public comment.

The PSHB protocols and strategic plan


The Department of Agriculture is the lead department in the PSHB strategic plan and action plan. The PSHB is a phytosanitary pest and has been gazetted as such, followed by the DFFE, which is in the process of getting the proposed list published for comment. 

The current national strategy does not mention the responsibilities of provincial, district or local government, nor landowners in the management of PSHB. This, Mbelengwa said, would be rectified in the update due to be initiated this financial year.

The Department of Agriculture published the amended PSHB control measures on 25 February 2025 as part of the Agricultural Pests Act, highlighting PSHB’s status as a quarantine pest and indicating the reporting procedures for new pests.

The amendment also highlights the prohibition relating to the removal, keeping, planting or cultivation of infested plant/weed.

The DFFE advised that when dealing with infected trees, the first step was to ensure that the damage caused by the PSHB beetle had been properly identified. 

When removing infected wood, note the amended regulations 4(2) regarding the movement of infected wood. Then ensure that the infected wood is either solarised at 70°C in a solarisation unit on site or chipped to 2cm before moving it.

The department warns not to move infected wood from an infected zone to a clean zone. The protocol is to dispose of the infected wood via incineration in the infected zone.

While municipalities and communities plan to manage the PSHB infestation as a long-term threat, investigations are ongoing by the Forestry and Agricultural Biotechnology Institute (Fabi) at the University of Pretoria, which has been exploring the possibility of introducing biological controls.

In 2024, Prof Brett Hurley and PhD candidate Garyn Townsend from Fabi visited central Vietnam, where they collected material from PSHB-infested acacia trees in the hope of identifying and testing natural enemies of the insect that could be used. These materials were being investigated, but there is limited funding to continue the studies. DM

https://www.youtube.com/watch?v=REeWvTRUpMk

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