Desperate drive to stop tree-killing beetle

The beetles make tunnels in trees to lay their eggs inside.

A volunteer group is using a combination of traps, trickery and triage in a desperate effort to save Arderne Gardens from an invasive tree-killing beetle.

The polyphagous shot hole borer poses the gravest threat to the public park since it was founded in 1845, says the Friends of Arderne Gardens (Fotag).

Fotag says it is executing a plan to stop the beetle from decimating champion trees in the gardens.

Just last week, the Tatler reported on confirmed new infestations in Observatory and Kenilworth (“Invasive, tree-killing beetle spreading,” Thursday March 2).

In a statement on Tuesday, the City said it had now recorded 191 infested trees, 104 on City-owned land and 87 on private properties in the southern suburbs.

Boxelders, London planes, English oaks and grey poplars are the trees being hardest hit in the southern suburbs, and so far, the beetle has reached Newlands, Kenilworth, Mowbray, Rondebosch, Observatory and Wynberg.

Fotag chairman Fracois Krige said they had worked with scientists from Stellenbosch University and the University of Pretoria’s Forestry and Agricultural Biotechnology Institute to develop a plan for the gardens.

They were hanging verbenone repellents in vulnerable champion trees and deploying lures and traps, he said.

“These help to trick the beetle into thinking that the trees are already infested and not an attractive host. Passing beetles are sexually attracted to the lure pheromone mimickers,” he said.

Verbenone is a beetle pheromone that signals that a tree is fully infested and the food supply is insufficient for additional beetles.

Mr Krige said they planned to pre-emptively remove boxelders (Acer negundo) within the gardens along with a few other low-value reproductive host species, such as the decayed oaks on the Herschel boundary, and some viburnum shrubs.

Boxelders accounted for over 90% of infested trees in the surrounding area and 100% of the outlier species and severely infested species, he said.

They were “amplifier” species, essentially the super-spreaders of the beetle, he said.

This week, the City started clearing infested trees from municipal land and called on residents to participate in a voluntary tree-replacement initiative that will be launched tomorrow, Friday March 10.

The first trees to be removed are infested boxelders along the Liesbeek River corridor, near the N2 highway and Liesbeek Park Way.

Access to these areas will be restricted while the work is under way with chainsaws and wood chipping machines. The beetle-infested chippings will then be transported to a site for incineration.

“It is a sad turn of events for all of us. As much as we value our trees – many of them are decades older than us – we do not have any alternative but to chip the infested trees. We are doing so in an effort to stop the beetle in its tracks and to save other trees from a similar fate,” said mayoral committee member for spatial planning and environment Eddie Andrews.

First to go, he said, would be the boxelders from City-owned land along major transport routes as those posed the biggest threat of spreading the beetle.

The City has also rolled-out free training for gardening and landscaping businesses and others that handle trees and plant material on how to prevent the spread of the beetle.

Mr Krige, an arborist, said he had been inundated with calls and emails about the beetle.

“We are discovering extremely rapid spread of the infestation daily. It is one of the most depressing and stressful times of my life. I think that Capetonians are unaware of how serious and devastating this will be in the next few years. Once the boxelder population crashes and the beetle moves on to the next tiers of susceptible species, we will be living in a transformed landscape. I am determined to do the best I can for the Arderne,” he said.

Report beetle sightings online at www.capetown.gov.za/ invasivespecies, by calling 021 4444 2357 or emailing invasive.species@captown.gov.za