30 May 2018
Steer clear of dying trees in George area
The George Municipality is warning people to steer clear of trees that appear to be dying as hundreds of trees in the city are starting to succumb to, mainly, borer beetle infestation.
The municipality reported last month (3 April 2018) that trees in George were showing signs of infestation with the Polyphagous Shot Hole Borer (PSHB) beetle and associated fungus, and had called upon expert advice from University of Pretoria Professor Wilhelm de Beer. It also asked the public to report trees they suspected of being infected.
George Municipal Manager Trevor Botha said the municipality was dismayed to hear the PSHB beetle and its associated fungus had not only decimated entire species in other parts of the world, but there was also little proven success in controlling it. “We are awaiting results of DNA sequence testing to confirm the local infestation is in fact the same beetle and fungus that have killed thousands of trees elsewhere, but Professor De Beer’s initial observations and the many trees that have started dying off, certainly point in that direction.
“There are hundreds of trees across the municipal area that show advanced symptoms and, for the moment, there seems to be no certain cure. We continue to work with Professor De Beer and the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria to find a solution, but must in the meantime address what we can.
“We ask the public to be especially careful near trees during and directly after adverse weather and wind, and ask that they help spread the message. We have identified Meade Street in the CBD the greatest immediate threat, where the fungus had accelerated the dying off of several trees that had 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. In George the most likely to be infected are box elder, maple and oak trees, which line many of the city’s streets – but these are not the only species that can be affected and we suggest people take heed as a general rule. Please note indigenous species can also be infected.”
Mr Botha said many of the trees in George were reaching maturity and had already been scheduled to be systematically replaced as they started dying off. However, the aggressive nature of the borer beetle combined with the effect of urban development (such as paving) and the mature age of the trees have resulted in trees dying faster than could have been anticipated – or planned or budgeted for.
“The municipality has been trimming dead branches from trees constantly, but will need to get in outside contractors to adequately address the problem. Cutting and trimming large trees is a specialist, dangerous and expensive task for which the municipality must find additional funding. While we are investigating all sources of funding, we appeal to the public to take care and tell others to do so also. 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,” said Botha.
The municipality had initially investigated a separate, specialised disposal site for infected trees, branches and plant material – where it could be burnt or solarised. However, the Western Cape Department of Environmental Affairs and Development Planning was not in favour of another disposal or burn site in the city. Since the impact and spread of the disease is currently faster than any proven control measure (hence out of control), it is also considered more prudent to focus efforts on safeguarding trees.
All infected stumps, branches and plant material must be taken to the municipal garden waste site on the Airport Road (R102) for disposal. Cut materials should preferably be moved off the premises to the waste site within 24 hours from being cut.
Tree felling companies, garden services and wood cutters are advised to dispose of plant material only at the garden waste site. Infected wood should NOT be turned into firewood for selling or chipped for mulching as the fungus remains active in this way.
Private property owners
It is recommended that owners regularly inspect trees on their properties for signs of disease and trim dead branches as they notice them. It is very important that nobody sit, play or linger under such trees and children should be warned to not climb in or play under such trees under any circumstances. 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,” said Botha.
Persons, businesses and organisations wanting to meaningfully assist can contact email@example.com
The George Municipality started investigating possible local infestation of the Polyphagous Shot Hole Borer (PSHB) beetle and its associated fungus following a scientific report in the Southern African Institute of Forestry (SAIF) newsletter in March2018. Since then hundreds of trees in the George municipal area have been identified to be infected by the disease.
Professor Wilhelm de Beer of the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria provided the following information:
The PSHB and its fungus was first discovered in South Africa during a routine survey for tree pests at the KwaZulu-Natal Botanical Gardens in August 2017, and is suspected to have come into the country via packaging in harbours. Native to Southeast Asia, it is a 2mm long ambrosia type beetle (which means it feeds on ambrosia produced by fungus) and is also known as Euwallacea fornicatus (Stompkopkewer in Afrikaans).
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 situation is worsened by the fact that the beetle and fungus is not host specific but seems to be 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 important 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.
As there is still relatively little known about the control of the PSHB beetle and its fungus, and because of its aggressive and non-selective targeting of species, it is recommended that infected host plants and trees be felled and the plant material burnt or solarised to limit spreading.
Herbicides are being tested, but at huge cost and has had limited success so far because the fungus has been killing trees faster than the herbicide can take effect. Some attempts at biological control have been made overseas but with little success.Last published 30 May 2018