Pesky bug brings a plague to city trees

18 February 2018 - 00:00 By FARREN COLLINS
Julian Ortlepp says that the infestation is serious and could change the city’s landscape if not addressed.
Julian Ortlepp says that the infestation is serious and could change the city’s landscape if not addressed.
Image: Moeletsi Mabe

Johannesburg's reputation as one of the most wooded cities in the world is under serious threat from an alien insect no bigger than a matchstick head.

A worrying report compiled by Johannesburg City Parks last month showed how shothole borers had decimated trees in the suburb of Craighall Park.

Areas such as Parkview, Sandton and Houghton are also severely affected by the tiny, 2.5mm-long beetles, which bore holes in trees and infect them with a deadly fungus.

The insect originally hails from Southeast Asia.

Tree experts and arborists in the city confirmed the infestation to the Sunday Times, saying it had spread to other parts of the city and was laying waste to trees in some of the city's oldest suburbs.

Tree surgeon Julian Ortlepp, from Treeworks, said he had seen infected trees in every suburb he works in, "and that is almost all the northern suburbs".

"Imagine losing all the English oaks and the liquid ambers."

He said that the city was at risk of losing thousands of trees, which could affect the ecology of the city.

"The trees help bring rain, help with [reducing] pollution and supply oxygen. It would drastically change our environment."

Neil Hill, an arborist from Urban Forest Tree Care Service, said there was no way of knowing how many trees were affected, but that the situation was "very serious".

"I believe it is the most serious problem facing our urban trees since I started working in the field of arboriculture over 20 years ago," Hill said.

According to the city's report, controlling the insect is very difficult, and it warned of the bug spreading quickly to other areas.

in numbers

• 6 million: the estimated number of trees in Johannesburg

• 2.5mm: the average length of a shothole borer

• 270: the number of tree varieties that can be infected by the shothole borer

The report read: "The trees at Craighall Park are highly infested by the borers and the damage caused is beyond reversal. [Almost] all box elder trees in the area are dead and only a few are remaining, but they are highly infested and declining. The borer is highly invasive and spreading to other areas is imminent."

Despite the report, Johannesburg City Parks arboriculturist Adelaide Kubayi said the extent of the problem was not yet known and that "scientific assessments" needed to be conducted across the city to determine the scale of the problem, starting with Craighall Park and Illovo.

"The city is reviewing the maintenance programme that will ensure that best horticultural practices are applied to curb the spread of the pest," said Kubayi.

She said the city would also consult the Department of Agriculture, Forestry and Fisheries for guidance.

"Although this pest is very difficult to control, the city will try its best to deal with the infestation."

City Parks estimates that there are more than six million trees in Johannesburg.

According to Hill, the trees most affected by the shothole borers include box elder, English oak, London plane, liquid amber, kapok, Australian flame, Chinese maple, paperbark and willow.

Experts are unsure how the insects arrived in South Africa but researchers at the Forestry and Agricultural Biotechnology Institute at the University of Pretoria first encountered them in Pietermaritzburg last year. There are also reports of shothole borers in Limpopo.