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.

A London plane tree infested with the polyphagous shot hole borer beetle.
A London plane tree on 11th Avenue in Norwood, marked for infestation with the polyphagous shot hole borer.

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.

PSHB-infested trees on 11th Avenue
PSHB stickers stretching as far as the eye can see.
Close-up of tree infested with the shot hole borer
See all the dark brown spots on the trunk? I believe those are borer holes.

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.

Trees on 6th Avenue in Melville
Sixth Avenue, Melville.

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.

Epping Road in Forest Town
A tree-lined street in Forest Town.

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?

Modderfontein Nature Reserve
The Modderfontein Reserve.
Rhodes Park dam
Rhodes Park, Kensington.

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:

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

Eli in Rhodes Park
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  • Reply Dalton K Adams November 21, 2019 at 11:53 am

    The nonchalance of that real estate agent is shocking. Some people really have no foresight. I do realize that Joburg has a myriad of problems, but losing its urban forest is just going to make things worse. As you probably know, Joburg has the largest urban forest of any city in the world and it would be a tragedy to lose it. Thank you for posting this and trying to spread the word.

    • Reply 2summers November 21, 2019 at 11:58 am

      I know I was also shocked! It’s all so disheartening.

      • Reply Leigh November 21, 2019 at 12:43 pm

        It’s absolutely shocking. And the estate agents response ridiculous. How will she sell houses when our beautiful tree lined streets have nothing? I live very close to Norwood and was absolutely horrified to learn some weeks back that these signs are related to the Borer Beetle. Whilst Jhb is not the most treeied city in the world it ranks amongst the top. I cannot imagine our city without its beautiful visage of trees. Just also heard the news that Botswana has lifted its ban on Elephant trophy hunting. Sorry, I knowhave completely unrelated….but It’s all so disheartening .
        Thank you for this post.
        Your suggestions are helpful to at least understand a little of what we can do.

        • Reply 2summers November 21, 2019 at 12:45 pm

          Thanks. I’m glad it helps just a little 🙂

  • Reply dizzylexa November 21, 2019 at 12:00 pm

    Great blog Heather – I read somewhere that the best way to describe this little teeny beetle is that is the size of a sesame seed. The infected Plane trees I’ve come across look like they have measles. It’s all very sad and scary.

    • Reply 2summers November 21, 2019 at 12:07 pm

      So sad. So scary 🙁

  • Reply Graham November 21, 2019 at 12:02 pm

    Thank you for a very informative article. Residents needs to be aware of the consequences of this plague.

  • Reply violetonlineisonline November 21, 2019 at 12:11 pm

    we are walking through future graveyards. As I walk, I realise the scale of this disaster.
    Melville, Parkview, Parktown North, Houghton, IT’S EVERYWHERE. Along Glenhove, the trees look terribly sick, like they are not going to make it through another season. In Melville, I can point out the trees that have already died. Note too the Jacarandas that should be in full green leaf. They too are affected. This morning I walked past Poppies who have a huge dead tree outside their restaurant. They’ve reported it to City Parks over and over and over. Nobody has come.

    • Reply 2summers November 21, 2019 at 12:13 pm

      Ugh, it’s so horrible. Incidentally, the expert in that podcast I’ve posted says he hasn’t found any infested jacarandas yet and doesn’t think they’re super susceptible. So that’s good news at least. But still, horrible.

      • Reply Ian November 21, 2019 at 1:45 pm

        I stand corrected, but I think many of the Jacarandas in Joburg are just coming to the end of their lives… Because they are water-intensive, I understand that when individual trees do die of old age, they will not be replaced with young Jacarandas (hopefully, though, they will be replaced with something!).

        • Reply 2summers November 21, 2019 at 1:47 pm

          Yes I’ve heard the same thing.

  • Reply Ian November 21, 2019 at 1:19 pm

    The loss of our trees in Joburg would be a MASSIVE disaster for all the reasons you’ve explained in your blog. Our trees are beautiful to look at and are an important source of mental and physical well-being for all of us who live here. They provide the best and most effective carbon sink this city will ever have. Without them, our air will be more polluted and we will all suffer from a myriad of ailments, including asthma and potentially cancer. Since there is no way of effectively getting rid of the PSHB, the best way to mitigate the devastating loss of our urban forest is to plant more, PSHB-resistant trees. NOW!!!

  • Reply Margaret Urban November 21, 2019 at 3:21 pm

    I’ve been sadly watching the borer get nearer and nearer to Killarney as I go on my regular walks; just a skip across the M1 now… at least half of our street trees are London planes; most of the others are elderly jacarandas. Killarney is losing 2 or 3 jacarandas a year. We lost another yesterday; it crashed into Whitehall; succumbed to a mixture of termites and bad pruning by City Parks which has encouraged them to get top heavy.
    Thanks for posting Heather; my recent experiences with estate agents has been pretty dire – many are not nearly as knowledgeable as they used to be.

    • Reply 2summers November 21, 2019 at 3:27 pm

      Ugh, so sad. And also about the jacarandas! I agree – real estate agents of all people should be well informed about this problem. I’m going to start talking about it to every agent I meet 🙂

  • Reply Catrina November 21, 2019 at 3:30 pm

    I had no idea. This is a desaster. As always with environmental issues, people will only notice when it starts affecting them personally – like when that short-sighted real estate agent’s trees will start dying in her backyard.
    Thanks for this post. I will be in Capetown for soon and I wonder how far PSHB has spread there. I hope people will realize how urgent and important this is.

    • Reply 2summers November 21, 2019 at 3:42 pm

      I also wonder…I haven’t heard much news of this from Cape Town but I imagine people don’t know about it, just like here 🙁

  • Reply Margaret Urban November 21, 2019 at 3:30 pm

    Perhaps ‘Celtis africana’, the white stinkwood, could be a replacement for dying jacarandas. It’s an excellent shade tree, though it doesn’t have showy flowers.
    I don’t see it on the lists so not sure if it is affected by PSHB

    • Reply 2summers November 21, 2019 at 3:41 pm

      Sounds like a good candidate to me!

  • Reply AutumnAshbough November 22, 2019 at 2:59 am

    The western bark beetle has devastated the Rockies and parts of Utah. I hate, hate, hate seeing the dead trees, especially now, when we need as many as we can get to combat climate change.

    • Reply 2summers November 22, 2019 at 6:14 am

      I know. It’s devastating! I haven’t heard of the western bark beetle.

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