Cape Town - After the discovery of an invasive Polyphagous Shot Hole Borer (PSHB) beetle infestation in Newlands last week, a number of further infestations of the tree-killing beetle are being seen across the metro, particularly in Rosebank and Mowbray.
Before the discovery in Newlands, trees in Somerset West only had been affected and removed, but now 12 locations have been recorded since Sunday.
Chairperson of the mayoral advisory committee for water quality, Alex Lansdowne, inspected the infected trees and confirmed the PSHB had entered the second stage of its colonisation in Cape Town.
He said the PSHB was always going to spread to the southern suburbs, which were heavily vegetated with trees; the job now was to work together to track and manage the spread.
Last year, local government MEC Anton Bredell said scientists had found that about 30% of urban trees were susceptible to PSHB.
He said Cape Town had an estimated four million trees and could expect to lose as many as a million to PSHB over the next decade.
Environmental NPO Parkscape and other organisations have advised that four boxelder trees in Rosebank – near the Liesbeek River – are also carrying the very destructive beetle.
Following assessments of the situation, deputy mayor and Spatial Planning and Environment Mayco member Eddie Andrews said: “The Liesbeek River has been identified as a priority pathway, more resources were allocated to conduct assessments to determine the extent and distribution of the beetle in the area.
“The City will soon commence with the removal of the trees on City-owned land that are infested with the PSHB (on public open spaces, river corridors, green belts, road verges, public parks and so forth).
“Unfortunately, the only way to prevent the spreading of the invasive beetle is to chip affected trees, and carefully remove the biomass under cover of heavy duty plastic and to incinerate it at an appropriate site… We request residents to report sightings to the City as soon as possible,” Andrews said.
Francois Roets, a conservation ecology and entomology professor at Stellenbosch University, explained: “The beetle bores into the vascular tissues of trees and introduces a fungus that it feeds on; it uses the living tree as a place to cultivate its fungal ‘crop’.
“Damaging of the vascular tissues by the beetle and blocking of vessels by fungal growth reduces the ability of the plant to transport water and nutrients from the roots.
“If there are enough infestations the plant simply cannot transport enough water and the tree usually then dies fairly rapidly with symptoms that are similar to those when trees are stressed by drought.
“Boxelder trees can die in as little as a year and the first English oaks will likely start dying off within four years of initial infestation,” Roets said.
