A black beetle is killing South Africa’s trees, and no one knows how to stop it. It arrived from Southeast Asia about four years ago; now, the polyphagous shot-hole borer has spread a thousand miles across South Africa, from the eastern city of Pietermaritzburg, where it was discovered in 2017, to indigenous forests on the west coast near Cape Town. An unwelcome side effect of globalisation, the pest is believed to have arrived along with wood pellets on a ship.
The polyphagous shot-hole borer, or PSHB, first drew scientific attention in 2008 after infesting avocado orchards in Israel and was then found burrowing into millions of trees in urban southern California. Now, South Africa is probably facing the largest invasion by surface area to date.
The pest is likely to drastically reduce the green canopy of Johannesburg, one of the largest man-made forests in the world, with some tree experts saying that as much as 30% of all trees could die. It could also hurt the country’s avocado, macadamia, wine, stone fruit and pecan nut industries, which account for a large slice of the nation’s $11 billion of agricultural exports. At risk too are the iconic oak trees of Stellenbosch, the de facto capital of South Africa’s scenic winelands.
Wilhelm de Beer, a forest pathologist at the University of Pretoria, is leading a nationwide PSHB network that includes researchers from eight universities. “Typically, these forest insects go for one particular tree. Now, we have something that is sitting on everything and that makes it so difficult to study, because some trees die in three years, some in five years and some don’t die at all. We can’t predict what’s going to happen.’’
The beetle has infested pecan nut orchards in the Northern Cape province, and the avocado industry in the north east of the country is monitoring for a potential outbreak. Macadamias, peaches and grapevines may also be affected, according to the Department of Agriculture, Forestry and Fisheries. While the government has pledged R5 million for research on pest control, most funds so far have come from commercial agriculture — pecan, macadamia and avocado farmers.