The clearest signs of shothole borer are tiny round entry holes in the bark, fine sawdust or dark staining on the trunk, and dieback in the crown as branches thin and die. The beetle itself is barely bigger than a sesame seed, so the bark tells the story long before the insect is ever seen.
The shothole borer is an ambrosia beetle that tunnels into the trunks and branches of trees. The beetles and the fungus they carry can kill a tree and spread to its neighbours, which is why early identification matters more with this pest than with almost any other tree problem on a Gauteng property.
This guide covers what the beetle is, the six signs to check for, which trees carry the greatest risk, and what to do, and what not to do, when you find signs on your property.
What the Shothole Borer Beetle Is
The shothole borer is a small beetle that tunnels into the trunks and branches of many tree species, where it breeds. The tunnels themselves are narrow, but the beetle carries a fungus that interferes with the tree’s water and nutrient movement, and it is this fungus, blocking the tree’s internal plumbing, that does the killing.
The species behind the damage in South African gardens is the polyphagous shothole borer, an invasive ambrosia beetle. Ambrosia beetles farm fungus inside their galleries rather than eating the wood itself, so a tree can be riddled with fungus-carrying tunnels while barely showing a chew mark. SANBI’s PlantZAfrica record describes it as an invasive beetle from Asia that was first recorded in South Africa in 2012.
For a property owner, two facts about the beetle’s biology drive every decision. It attacks many unrelated tree species, so no garden is automatically safe. And it moves from tree to tree, so one infested trunk is never only one tree’s problem.
The Signs of Shothole Borer in a Tree
The earlier an infestation is found, the more treatment can do. These are the usual signs, in the order they tend to appear.
| Sign | What you see |
|---|---|
| Tiny holes in the bark | Small round entry holes in the trunk or branches, as if the bark has been hit by shotgun shot, which gives the beetle its name |
| Sawdust and staining | Fine sawdust pushed out of the holes, or dark staining and gum on the bark |
| Dieback in the crown | Branches thinning and dying back as the infestation takes hold |
| Cracked or dying bark | Bark that cracks, weeps or falls away as the tunnels spread underneath it |
| Woodpecker activity | Birds pecking at the trunk, often a sign that beetles are at work beneath the bark |
| One tree struggling near others | The borer moves from tree to tree, so check nearby trees when one shows signs |
How to inspect your own trees
Walk the trunk slowly and look at eye level first. Entry holes are about the size of a pen tip, so you are looking for stippling rather than holes you could poke a finger into. Sawdust collects in bark crevices and in cobwebbed clumps on the bark below fresh holes, and staining often shows as dark patches or gummy streaks where the tree is trying to wall off the invasion.
Then look up. Crown dieback is the sign most often missed, because thin branches at the top of a tall tree read as drought stress or ordinary seasonal die-off. On an infested tree the dieback spreads branch by branch over months, and by the time the whole crown looks sick, the trunk is usually carrying a heavy beetle population.
Signs that are easy to misread
Not every hole in bark is a borer. Woodpeckers, other beetles and natural bark splitting all leave marks. The combination that points to shothole borer is round entry holes together with fine sawdust or dark staining on the same patch of trunk, especially when the crown is thinning at the same time.
Which Trees Are Most at Risk
The polyphagous shothole borer attacks a wide range of tree species, which is what the name polyphagous means, many-fooded. Exotic and indigenous trees, street trees and garden specimens have all been attacked in South Africa. SANBI’s record for the English oak describes trees in Cape Town being colonised and killed by the beetle, and oaks remain one of the species gardeners most associate with the pest.
Stressed trees are the common thread. Drought-stressed, wounded or poorly sited trees are more attractive to the beetle than vigorous ones, so keeping trees watered through dry winters and avoiding unnecessary bark damage is genuine prevention, not just garden-variety advice.
Treat any mature tree showing the signs above as worth checking, whatever the species, and check its neighbours at the same time. Because the beetle spreads tree to tree, the risk on your property is about position and condition as much as species.
What to Do If You See Signs
Work through these steps in order. The order matters, because the wrong first move can spread the beetle faster than leaving the tree alone would.
- Check the surrounding trees. The borer moves from tree to tree, so inspect every tree within reach of the affected one before deciding anything else.
- Get a professional inspection before cutting. A trained eye confirms the signs and tells you honestly which trees can be treated and which are beyond saving. Tree inspections of this kind are free from a tree service that treats borer.
- Do not move infested wood off the property. Cut branches, trunks and firewood from an infested tree can carry live beetles, and moving wood between properties is one of the main ways the pest spreads. Leave it on site until a professional advises on safe disposal or treatment.
- Follow the treatment programme for trees that can be saved. Treatment combines specialised insecticide treatment on affected trees with preventive measures to protect the healthy trees nearby, followed by monitoring so any re-infestation is caught early.
- Remove trees that cannot be saved. Heavily infested trees that are beyond treatment are removed safely to stop the beetle breeding, because a dead, beetle-filled trunk standing in the garden is a launch pad for the rest of the property.
Common Mistakes to Avoid
Most borer disasters on suburban properties follow the same few wrong turns.
- Ignoring early dieback. Reading crown thinning as drought or winter and waiting a season to see is the single biggest delay. By the next spring the infestation has usually moved to neighbouring trees.
- Pruning and transporting infested wood. Cutting out infested branches and hauling them to the dump or to a friend’s fireplace moves live beetles to new food. Do not move infested wood off site.
- Assuming a heavily infested tree can be saved. Treatment works best on trees caught early. A tree with cracked bark, heavy staining and a dying crown is usually past saving, and keeping it standing keeps the nursery open.
- Waiting for the tree to look better on its own. Unlike stress-related dieback, shothole borer infestations do not recover without intervention, and delay removes options.
- Moving firewood between properties. Firewood is the classic hitchhike for the beetle. Buy and burn locally, and keep wood from any suspect tree on the property it came from.
Frequently Asked Questions
Can a tree survive shothole borer?
It depends how far the infestation has progressed. Trees treated early have the best chance, while trees that are too far gone are best removed to stop the beetle spreading to their neighbours. A professional inspection gives an honest verdict either way.
Should I remove an infested tree immediately?
Not before an assessment. Removal is the right call when the tree cannot be saved, because a dead infested trunk breeds beetles that attack the rest of the garden. A professional inspection confirms which case you have, and the wood stays on site either way.
How does shothole borer spread?
The beetle flies from tree to tree, and infested wood moved between properties carries it much further. Firewood, cut branches and trunks from an infested tree can all hold live beetles, which is why infested material should never leave the property.
Can I treat shothole borer myself?
Effective treatment is a specialised insecticide programme applied by a trained team, combined with preventive treatment for nearby healthy trees. At home you can keep trees healthy with proper watering and pruning and avoid moving firewood, then call for treatment as soon as signs appear.
Get help with a borer-infested tree. Tree Wise Tree Felling inspects trees free of charge across greater Johannesburg and Gauteng from its Randburg base, says honestly which trees can be treated and which are beyond saving, and gives a fixed quote before any work starts. Get a quote.
Disclaimer. This article is general information, not a tree-health diagnosis. Shothole borer signs can resemble other bark and branch problems, and only a professional inspection can confirm an infestation and the right course of action for your trees.