A 2mm beetle is laying waste to George's trees

30 May 2018 - 09:50 By Dave Chambers
A close-up of the 2mm polyphagous shot hole borer beetle.
A close-up of the 2mm polyphagous shot hole borer beetle.
Image: George Municipality

Out of-control borer beetles are destroying hundreds of trees in the southern Cape.

Residents should steer clear of dying trees because of the danger of falling branches‚ officials in George warned on Wednesday.

“We ask the public to be especially careful near trees during and directly after adverse weather and wind‚” said municipal manager Trevor Botha.

“We have identified Meade Street in the CBD as the greatest immediate threat‚ where the fungus has accelerated the dying off of several trees that have reached maturity.

“Please take a good look at a tree before you walk‚ park‚ stand or picnic under it and avoid trees with signs of dying‚ such as broken branches.”

Elevated blue-black lesions on a tree’s bark, resembling shotgun wounds or cigarette burns, indicate borer beetle infestation.
Elevated blue-black lesions on a tree’s bark, resembling shotgun wounds or cigarette burns, indicate borer beetle infestation.
Image: George Municipality

Botha said the polyphagous shot hole borer beetle and its associated fungus had wiped out entire species elsewhere in the world‚ and there was little proven success in controlling it. The fungus killed trees more rapidly than herbicides could take effect.

The municipality is working with microbiologist Wilhelm de Beer‚ from the Forestry and Agricultural Biotechnology Institute at the University of Pretoria‚ and is awaiting the results of DNA sequence testing to see if the beetle responsible for the carnage is the same one that has laid waste to trees elsewhere.

“Professor de Beer’s initial observations and the many trees that have started dying off certainly point in that direction‚” said Botha. “There are hundreds of trees across the municipal area that show advanced symptoms and‚ for the moment‚ there seems to be no certain cure.”

The municipality planned to employ contractors to deal with ailing trees. “Cutting and trimming large trees is a specialist‚ dangerous and expensive task for which the municipality must find additional funding‚” he said.

“For now‚ we are concentrating on trimming branches on the major routes in town. Should it become necessary‚ the municipality will consider temporarily closing sections of roads and sidewalks.”

The municipality warned that infected wood must be taken to the town’s municipal waste site and not turned into firewood or chipped for mulching‚ as the fungus remained active.

“It is very important that nobody sit‚ play or linger under affected trees and children should be warned to not climb in or play under such trees under any circumstances‚” said Botha.

A polyphagous shot hole borer beetle on a man’s hand.
A polyphagous shot hole borer beetle on a man’s hand.
Image: George Municipality

“It is highly recommended that dying trees be felled‚ removed and the plant materials burned. Do not leave the tree stump untreated and do not replant in the exact same spot where the infected tree was‚ as evidence exists that beetles may bore down when a tree is cut.

“We have had to come to terms with the fact that‚ as with other cities that have been invaded by this beetle and fungus‚ our urban landscape is going to change. We will lose many of our large trees‚ which will sadly change some of the character of our city.

“But we are determined to plant new trees wherever we can‚ repopulating our city with indigenous species that have so far proven resistant to the beetle. We thank the public in advance for their help and support.”

The polyphagous shot hole borer beetle and its fungus were discovered in South Africa during a routine survey for tree pests at the KwaZulu-Natal Botanical Gardens in August 2017.

The beetle is suspected to have come into the country via packaging in harbours. Native to south-east Asia‚ it is a 2mm beetle known as Euwallacea fornicatus (Stompkopkewer in Afrikaans).

Professor Wilhelm de Beer takes samples from a tree in the Garden Route Botanical Garden.
Professor Wilhelm de Beer takes samples from a tree in the Garden Route Botanical Garden.
Image: George Municipality

The beetle bores through the bark into the sapwood of trees and inoculates the fungus into living wood. The fungus grows in the beetle’s tunnels and serves as food for its larvae. In susceptible trees‚ the fungus can spread through the sapwood causing disease and even death.

The beetle and fungus is affecting a wide range of indigenous and exotic trees‚ including box elder‚ Chinese and Japanese maple‚ oak‚ plane trees‚ Kapok trees‚ paper bark acacia‚ wild plum‚ dwarf corral and common corral.

Overseas surveys have also indicated susceptibility of crop trees such as avocado‚ macadamia‚ pecan‚ peach‚ orange and grapevine.

Symptoms most seen on trees in George so far are small elevated blue-black lesions on the bark resembling shotgun wounds or cigarette burns. Other symptoms include patches of white powdered wood on the bark surrounding entrance holes of beetle tunnels and blotches of oozing resin on the bark. 

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