What to do when you have trees infected with the shot hole borer beetle

A plane tree, which is highly susceptible to the borer beetle.

Once you have established that you have trees in your garden that are infected by

the polyphagous shot hole borer beetle (PSHB), and you have filled out the form for the City of Cape Town’s invasive species unit, this is what you need to do next.

When your trees are infected with the PSHB, it is the fungus (Fusarium euwallaceae) that is killing your trees.

So, you need to kill the fungus in your tree. The fungus provides food for the adult beetles and their larvae.

The fungus grows on the outer part of the tree trunk, in the cambium and phloem “ring”. Beetles can burrow quite deep – up to 50cm in some of the trees.

However, it appears that the fungus concentrates in a 3cm to 6cm ring immediately below the bark of the tree. This ring, however, stretches from the roots to the very crown of the tree.

It is thought that the beetles are not in the very tops of the trees, but up to about 4m high. That means that you need to apply fungicide rather high up into the trees for sufficient fungicide to penetrate the bark and be effective against the fungus.

There is one fungicide currently registered in South Africa that appears to be effective in killing this fungus. The product developed by Pan African Farms (panafricanfarms.co.za) is called PSHB Fungicidal, and can be ordered directly from the company.

The application of the fungicide will need spray equipment that can reach high into infected trees. For the fungicide to be drawn into the bark, a large volume of water is needed, thus a large spray droplet nozzle must be used. Misting sprays will not be effective.

Random Harvest Indigenous Nursery in Gauteng have been using this product to treat trees in Johannesburg successfully for the past two years, and there is information on their website (randomharvest.co.za) and Facebook pages.

In addition to treating your trees with fungicide, provide your trees with food and water. In the hot summer months in the Western Cape, our trees are stressed, and this makes them more susceptible to all kinds of pests and diseases, including the PSHB.

Providing your trees with a good soaking of water once a week will help. Feed your trees with organic fertiliser, either granular or in liquid, every two weeks during the growing season.

If your trees are small enough to do foliar applications, that works well. If not, do soil applications from the drip line of the tree back towards the trunk. The drip line is the end of the outermost branches of the tree.

If you suspect that you have this beetle infesting trees in your yard or in your street, please take action. It is vital that we do our absolute best to eradicate this pest.

The list of trees being infected and potentially dying grows almost daily. If we do not act, we will lose thousands of trees in the Western Cape.

Losing trees in your immediate area will change the wildlife and the micro-climate in your area. There are streets in Johannesburg where every street tree has been cut down. The temperatures in these streets on average was between 5°C and 9°C hotter than before the trees were removed.

That is an enormous difference. It is not only the trees in our gardens and streets that are at risk, but in our national parks and veld too. We can all do our part to help. For more information, or to see previous articles we’ve published on this subject, visit www.bolanderlifestyle.co.za