The Shot Hole Borer Beetle: A Deadly Threat to Joburg's Trees

I struggled to decide how to title this post, as the title above feels like an understatement. While the polyphagous shot hole borer (PSHB) beetle is first and foremost a killer of trees, this insect could also kill our city.

And PSHB is not only a threat to Joburg. It’s infesting trees all over South Africa and could eventually spread to the rest of the African continent.

I’m not an expert on the shot hole borer and I know very little about trees, other than how freaking awesome they are. There’s a lot of confusing and conflicting information about PSHB floating around and I’ll undoubtedly get things wrong here. But I’m distressed by how few people seem to be aware of this grave threat. I’d like to use this blog to change that.

So please bear with me (bore with me?) as I try to lay out the basics on what the shot hole borer is, what it’s doing to our trees, and what we can do to fight it.

What is the Shot Hole Borer?

The shot hole borer, also known as PSHB (the P stands for polyphagous, which means the beetle can feed on multiple types of trees), is a two-millimeter-sized beetle that comes from Vietnam. It was first discovered in South Africa in 2017, at the national botanical garden in Durban, but many experts believe the beetle made its way here years earlier. PSHB has also spread to other parts of the world, including Israel and California.

The beetle infests trees by tunnelling deep into the trunk or branches and depositing a fungus that effectively poisons – and eventually kills – the tree. If the tree is a PSHB “reproductive host” species, then the borer will reproduce in the tree at an alarming rate: A reproductive host tree can house up to 100,000 borer beetles. The offspring then fly out of the host tree and infest more trees.

Many of the trees affected by PSHB in South Africa are “exotic” species native to Europe and other places – plane trees, oak trees, maple trees, fruit trees, etc. But many indigenous South African species are also vulnerable to PSHB.

PSHB has been spreading in South Africa for at least three years, and tens of thousands of trees have potentially been affected already. Predictions vary regarding how many trees could ultimately die. But some experts predict Joburg could lose more than 30% – i.e. at least a couple of million – of its trees.

Why Do I Care?

Research and environmental action groups have begun marking PSHB-infested trees in Joburg with large, red-and-white stickers. A couple of weeks ago, while driving down 11th Avenue between Rosebank and Norwood, I noticed nearly every tree within a two-kilometer stretch had a sticker on it.

The stickers read:

“This tree has been killed by the Polyphagous Shot Hole Borer Beetle. The PSHB is a new invasive pest in South Africa that is killing both indigenous and exotics (sic) trees. This tree is now a PSHB breeding area and contains hundreds of thousands of beetles. This beetle is smaller than a grain of rice, when it emerges it will fly and attack the surrounding trees killing them too. This tree needs to be removed and the infested wood disposed of responsibly so that the beetles within are destroyed.

Parts of the sticker text have been crossed out, perhaps due to a lack consensus about if/when these trees will die (they’re definitely not dead yet) and what is the best course of action for dealing with them.

Even though I’d been aware of PSHB for some time, seeing this endless row of presumably soon-to-be-dead trees was a massive shock.

A bit later I was making small talk with a woman I’d never met before – a real estate agent in Norwood. I asked her if she’d seen the long row of stickers and if she had any idea what would happen to those trees.

“Oh, I was wondering what those stickers meant,” the woman replied absently. I explained what I knew about the shot hole borer and how it’s killing hoards of trees. She shrugged.

“This city has bigger problems than dead trees,” she said.

That is when I decided to write this blog post.

The Potential Impact of PSHB

I suppose I can understand where that woman’s comment was coming from. Johannesburg (and South Africa more generally) has massive problems with poverty, crime, lack of basic services, xenophobia, corruption, violence against women, an economic recession, etc. etc. etc. Who cares about a few million dead trees, especially dead trees that aren’t even indigenous?

I’ll answer that question with a photo.

This is Melville’s 6th Avenue, the street where I live, as it looked yesterday afternoon. The trees you see here are London plane trees, highly susceptible to becoming PSHB reproductive hosts.

Imagine what this street will look like if/when these trees are gone.

Imagine the thousands (literally thousands) of other Joburg streets – in Sandton, Parktown, Greenside, Linksfield, Brixton, Kensington, Norwood, Rosebank, Saxonwold, Craighall, Northcliff, Orange Grove, Albertville, Bez Valley, Yeoville, Bertrams, Berea, Troyeville, and dozens of other suburbs – that look much like this one. Now imagine those streets stripped of trees.

Imagine the public parks – Emmarentia Dam, Delta Park, Modderfontein, James and Ethel Gray Park, the Joburg Zoo, Joubert Park – with hundreds of stumps where trees used to stand. Imagine the millions of birds and insects and other animals that live in and eat from those trees. Where will they go?

Imagine the summer sun beating down on your house without any shade. Imagine the heat. Imagine that cloud of smokey pollution that hangs on the city’s horizon every year in August and September, before the rains come, and how much thicker that cloud will be with 30% fewer trees to absorb it. Imagine the impact on our agricultural sectors. Imagine the erosion. Imagine the CO2 emissions.

Imagine the loss of our cultural heritage. Imagine the dip in tourism to a city billed as “the world’s largest urban forest”, after that forest is severely diminished. Imagine your plummeting property values. Imagine the reduced quality of life for every living thing in Joburg.

The looming death of our trees is catastrophic.

What to Do About Shot Hole Borer

There is no proven way to stop or cure PSHB (and this is really fu*king scary). But there are various measures we can take to contain the spread.

Unfortunately, according to most of what I’ve heard and read, the City of Joburg is lagging behind in its response to the crisis. At the very least the city needs a designated dumping site for trees infested with PSHB, where the wood can be chipped and dried in the sun under plastic sheets (which kills the beetle). Otherwise the borer can live inside the firewood of dead trees and spread further and further afield as the wood is distributed.

But anyway, this hasn’t happened yet. So here are a few things we as individuals can do right now:

• Tell everyone you know about PSHB. According to my very informal research, at least 90% of Joburgers have no idea this problem exists. Talk to your friends. Talk about it on social media and in community chat groups.
• Knowledge is power. Read up on the issue. A few sources I’ve found helpful are the Johannesburg Urban Forest Alliance (JUFA), the Forestry and Agricultural Biotechnology Institute (FABI), Arbour Solutions, the Shot Hole Borer Action Group on Facebook, and this Chai FM radio interview with local tree expert Julian Ortlepp.
• Take a look at the trees around your home. If you suspect one of your trees is infested, contact an arborist to do an assessment, remove dead trees, and provide guidance on holistic methods to treat live trees. TreeWorks and Landscape Guru are two companies that do this, and Arbour Solutions has a treatment (not a cure) that can potentially stave off the death of a tree.
• Keep your healthy trees healthy by mulching, watering, and providing natural fertilizers. An arborist can advise you on this.
• Report dead or infested trees in public spaces to Joburg City Parks and JUFA ([email protected]).
• Don’t buy/use firewood unless you know where it came from.
• PLANT NEW TREES, especially indigenous trees that aren’t susceptible to PSHB. Browse a list of vulnerable trees here.

Let’s save our trees, our city, and ourselves.