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Recently we had the privilege of hosting a speaker, Paul Barker, who works closely with identifying and eradicating the Polyphagous Shot Hole Borer The Polyphagous Shot Hole Borer (PSHB) is an invasive beetle native to Southeast Asia that has seriously threatened South Africa's trees. The first detection was in 2017 on London Plane trees in the KwaZulu-Natal National Botanical Gardens in Pietermaritzburg. The PSHB has since spread to multiple locations across eight provinces. This tiny beetle, about the size of a sesame seed, may seem insignificant, but it carries with it a deadly companion: the fungus Fusarium euwallaceae. The beetle has a symbiotic relationship with this fungus, which it uses as a food source for itself and its larvae. Unfortunately, this fungus is also a tree killer. In susceptible trees, it causes a disease known as Fusarium dieback, which leads to dying branches and, ultimately, tree death.  The Threat to South Africa's Trees PSHB poses a significant risk to a wide range of exotic and indigenous trees in urban, agricultural, and natural landscapes. While the beetle attacks many tree species, it cannot complete its life cycle on all of them. Trees in which the beetle can breed and multiply are known as "reproductive host trees." These include important species such as oaks, maples, willows, coral trees, avocados, and castor beans. On these trees, the beetle establishes galleries (tunnels) where it breeds, and the fungus it carries can thrive, leading to severe damage or tree death. Conversely, there are "non-reproductive host trees" where the beetle may attack but does not establish galleries or breed. The fungus may or may not cause disease on these trees, and they are generally not expected to die. However, the presence of the beetle on any tree is a cause for concern due to the potential for the spread of the fungus. Species at Risk Among the species where both the beetle and fungus flourish are the Box Elder, Weeping Willow, English Oak, and Castor Bean. However, these are not the only species at risk. The PSHB and its associated fungus have been found in a wide variety of tree species across South Africa. For a complete list of affected species, please refer to the attached documentation. Please see attached documents for full plant species lists and more information. Preventing the Spread of PSHB One of the most significant means of spreading this beetle is the movement of infested wood, most importantly, firewood. Proper disposal of infested trees is crucial in reducing the spread of this damaging pest. Methods such as chipping, composting, or solarization of wood are recommended to prevent further infestation. Solarization can be achieved by placing chips in direct sunlight and covering the pile with plastic. Burning is not recommended as the smoke and heat will make the beetles disperse out of the wood before burning is completed. Ongoing surveys are being conducted to monitor the spread of the PSHB across South Africa. Public awareness and involvement are vital to this effort. You can assist by keeping an eye out for symptoms of infestation in your local area and reporting any suspicious activity to the relevant authorities. What You Can Do
By staying informed and vigilant, we can help protect South Africa’s trees from the devastating effects of the Polyphagous Shot Hole Borer. Remember - Burn it where you buy it! 
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AuthorGVB Conservancy Staff Archives
May 2025
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