What is all the Crisis about?
If you are not aware of the tree crisis that we are facing caused by these tiny destructive shot hole borer beetles, please keep an eye open on your trees or trees in your neighbourhood, as the Shot Hole borer beetle has become a major problem in South Africa, and has already caused significant damage to trees in our Country’s eco-system.
Johannesburg City Parks and Zoo, the custodians of the City of Joburg’s trees, of which we all see in our Parks and on pavements, have met with their counterparts for urban forestry in government; research institutions; tree maintenance service providers and its internal teams to outline its plan of action in tackling the outbreak and the extent of the infestation and damage caused by the Polyphagous Shothole Borer (PSHB) – which simply put- carries fungal spores that infects and eventually kills trees off.
The shot hole borer, is a very small beetle that is an evasive species that was introduced into South Africa from Asia in 2017, and was first encountered in KZN, and has slowly started spreading across the country, putting most trees at risk of infestation. The beetle initially embeds its larvae in the inner parts of a tree, and when the larvae is fully developed, it makes its way out to the surface of the tree, and in the process of doing this it causes damage or lesions to the tree done by their tunnelling process, which causes tiny small holes on the surface of the tree, and its these holes and tunnels that’s been created that has a major effect on the trees growth by reducing the amount of nutrients the tree receives through its veins, and results in a tree that is not sending enough nutrients to the top of the tree, and one will start seeing trees that look diseased from the top of them, and will cause them to slowly start dying off. Further to this and compounding the problem is the female beetle carries a fungus (Fusarium euwallaceae) that is left in these tunnels that creates a feeding ground for the larvae and adult beetles, and it is this compounded problem that kills a tree.
So what can be done?
People enquire what can be done to save their tree that has infestation. The simple answer, is that there is no solution or formulation available that is registered with the Department of Agriculture for the treatment against shot hole borer, as it is an evasive specie of borer beetle. From what we have researched, we are sharing information on the best practises to follow. Successful trial have been done in the USA, however these have been undertaken by their local authorities and experts with their own registered formulations for the shot hole borer beetle.
With Shot hole borer beetle, the first thing to establish is if the tree has infestation, so one needs to examine the tree and see if it indeed is infested by shot hole borer.
If it is infested, one has to try ensure the infested tree doesn’t cross infest healthy trees, but unfortunately the reality is there is no single solution to eradicate these borer beetle, as a treatment that is successful will require multiple strategies and using multiple products repeated over a number of years. There are no pesticide products developed and registered for us against the Shot hole borer, due to it being an evasive ambrosia specie of borer beetle that attacks living trees, and if any type of fumigation gas was used (as in the case of conventional processed wood treatments to non-living timber) it would kill the tree and surrounding vegetation, and would be too greater a risk to treat and would not be a practical solution.
Some nurseries offer over the shelf products that would need to be injected deep into the borer holes on trees, this may work, but excessive amount may be required to be injected to be effective, and can be counterproductive. One needs to consider the risk associated to the surrounding environment around the tree before this is attempted.
The surface spraying of the tree or bark does not work and is simply a waste of time and money. If a pesticide applied can penetrate bark and you have the beginning stages of the borer in your tree, this may help, but in most cases it does not work.
Has my tree been infested?
There are a few signs to look out for. First one is sawdust type powder collecting on the base of the tree or on the bark, with small tiny surface holes. One may even see a type of liquid coming out these holes.
At the end of the day, these beetles are very opportunistic and most trees are targeted, as long as they can provide the correct ecosystem for the beetle to breed and thrive in.
Female beetles can fly almost a kilometre, but in most cases, they choose to fly and take over the closest tree they land on that is suitable to them. In heavily infested scenarios, one tree can harbour up to 100 000 beetles.
When a heavily infested tree is encountered, it needs to be either removed or treated straight away without delay, else the risk of cross infestation is at its highest, and adjoining trees could and most probably will be targeted. Dead trees or removed trees need to be carefully removed and disposed of as the timber will still be a breeding ground for the beetles.
Can you save your tree?
In summary- If caught soon enough, yes the tree can be saved, but if left too late, it becomes challenging to save it if it’s heavily infested. When a tree is stressed and attacked like this, it becomes weak and its capability to resist borer attack becomes less likely.
One can help by improving the health of your trees, such as providing adequate water through drier periods, build up a type of mulch to retain moisture around the base of the tree for the roots. Improve health by adding good compost and bio- stimulants to the soil around the trees, which can be obtained from your local nursery.
As mentioned above in “what can be done” reactive treatments can be attempted and will require repeated treatments every 6 months to see results.
You must further notify your neighbours or local residence association of a finding and create that awareness in your area when the borer are found. Warn people via social media is a good way that the word can be spread to create that awareness in your area. If you do find infestation in your tree, take action and report it to your local municipality or City Parks, and find out what they are doing about the shot hole borer crisis. If they do come out, please remember to have them remove dead trees and find out how they are responsibly destroying the trees.
Methods of treatment
To have any effect on the shot hole borer, one needs to have an effective treatments undertaken, and this requires the use of a fungicide and an insecticide getting into the infested trees. This can be achieved primarily by doing a tree injection treatment. This needs to be done with specialised equipment though to ensure the active ingredient in the insecticide and fungicide is injected deep enough into the tree within the borer exit holes, and the chemicals will be distributed by the tree via its vascular flow. From what we have researched, this is the most successful form of treatment.
There are three other types of treatments that have been attempted but are not effective enough, and these are a soil drench application to the soil around the base of the tree. This just pollutes the soil and has shown poor results when tested.
The use of irrigation pipes has been tested, and also failed to deliver the desired results. This method involves burying irrigation pipes below the surface of the ground by trees and delivering the product below ground level to avoid surface contact with animals and humans, of which is also providing poor results.
A bark penetrating pesticide can be applied to the bark on the tree trunk, as opposed to the whole crown of the tree. This method would help in new infestation sightings, but would not be effective in heavily infested trees. Disadvantage is there is limited local product available to render the treatment with.
What does one do when the tree is dead?
Most people will only notice a problem when their tree dies off, and still don’t know what caused it to die when it’s found. Some people think it’s attributed to natural causes due to nature, only to be found upon close inspection after the tree is cut down that the borer tunnels within the tree become visible.
When a tree dies, and it’s got confirmed signs of shot hole borer beetle in it, it is imperative to dispose of the tree the correct ways to avoid cross infestation to other trees. There are a few ways to do this correctly:
The best option is to have the timber of the dead tree burnt onsite. This needs to be done in a controlled way, and necessary permission obtained from your local authorities.
Disposing of the wood at designated dump sites is another option, for where it can be destroyed, however currently there are no dedicated dump sites for disposing of PSHB in South Africa. If you want to pursue this option, its best to contact your local municipality or Department of City Parks for further guidance.
Another option to look at, is what is called solarisation of the infested wood. This entails covering the pile of wood with a thick plastic sheet. Sealing the edges of the sheeting around the edges to ensure the heat and moisture are maintained and build up inside the sealed pile of wood. The disadvantage is this is a slow process, and the pile of wood needs to remain sealed for approximately eight weeks, which will kill all the shot hole borer inside the sealed heap of wood.
Once the tree is removed, one will be left with a tree stump, if possible have this removed to avoid any possible re-infestation, if not possible to remove, monitor the stump closely for any possible signs of infestation. If infestation does return, one can simply apply the solarisation process and cover the stump as directed above to kill off any remnants of the borer.
Here Is a link to the City of Joburg media statement about the shot hole borer crisis