The death of trees?
Indigenous and exotic trees in South Africa are dying by the thousands because of a tiny beetle that experts say is “impossible to eliminate”.
The beetle is only two millimetres in size and can be extremely difficult to spot.
The destructive polyphagous (able to feed on various kinds of foods) shot hole borer beetle has already infested thousands of trees and plants in the country and is expected to reach all corners of SA by 2022, killing off and damaging hundreds of species of trees. And while this happens, desperate calls to register chemicals to treat the trees have fallen on deaf ears.
The polyphagous shot hole borer beetle was first discovered in 2017 in Pietermaritzburg’s KwaZulu-Natal National Botanical Gardens in the historic avenue of London Plane Trees by researcher Dr Trudy Paap.
Although the beetle’s existence in SA was only discovered in 2017, Paap said at the time that the beetle had been in the country for at least five years and had already infected most of the London Plane Trees in the gardens that were planted in 1908.
Experts have said the beetle has spread across the country with the hardest hit areas being around Gauteng first, Johannesburg second and KwaZulu-Natal third.
The beetle is native to south-east Asia and is two millimetres in size — less than half the size of a nano sim card.
It has already been identified as the cause of massive tree deaths in the Gauteng urban areas as well as in George and Knysna.
The beetle is thought to have been brought into the country through wooden shipping pallets, although this cannot be confirmed.
The beetle has spread across the country through the transportation of fire wood and nursery trees as well as wind. The beetles can also fly to reach their next host.
Tree Treatment’s Hilton Fryer said the beetle is a much bigger problem than most people realise.
He said that using factors such as tree density, he had created a national four-year forecast model which projects the beetle achieving maximum infestation of trees over a seven-year period. “The model projects that the beetle will have reached all parts of South Africa by 2022,” said Fryer.
He said his forecast for KwaZulu-Natal in the next few years would “be bad” as “the dense indigenous forests create conduits which helps the borer to spread”.
He said trees most affected in KwaZulu-Natal are the Natal Fig as well as the Castor Bean.
He said, at the moment, the total infestation in Johannesburg is around 10% of its trees. The percentage would increase over a number of years if the beetle is allowed to spread, he added.
“The most difficult thing to realise is that there is no way the beetle can be controlled in South Africa. Any efforts to control it would not be effective as the beetle has embedded itself throughout the country. The outcome for indigenous forests on the Dolphin Coast are very poor.”
University of KwaZulu-Natal Plant Pathology senior professor Mark Laing, said although the London Plane Trees had been infected in the Botanical Gardens, they seemed to be quite hardy and looked better than he had expected them to.
He said infection depended on the type of tree and the amount of stress on the tree.
He said trees in urban areas were particularly vulnerable to stress, especially if they were planted along streets as the movement of their roots and their growth is restricted. “A friend of mine suspected her litchi tree along Howick Road was infested. I went out to have a look and the 30-metre tree was stone dead, thanks to the borer.”
Fryer said he had performed a survey trip two weeks ago to various places, including parts of KZN.
“I did see symptoms of the beetle on the street trees and in Pietermaritzburg’s botanical gardens.
“The avenue of London Plane Trees in the city are looking a lot better than the infested London Planes in Johannesburg.
“The beetle spreads very quickly. A year ago, the areas that are now infected in Johannesburg weren’t before. We did a community walk a year ago in Parkwood [a suburb in Johannesburg] and we could not find any evidence of the beetle.
“One year later we now know of many places where the beetle has penetrated the suburb.”
Fryer said he had created maps of the different provinces in the country with the number of incidents of the beetle reported using the Tree Survey mobile app that enables the public to report incidents of the beetle.
“The blank spaces on the map do not necessarily indicate that the beetle hasn’t reached those areas, we just have a lack of data,” he said.
“The beetle spreads quickly in a short space of time. If a tree is infested you have to either treat it or remove it or else the beetles will breed and spread.”
He said there had been experimental trials for various chemicals to treat the trees and kill the beetle, but none of the chemicals have been registered.
“The registrar from the National Department of Agriculture, Forest and Fisheries (DAFF) had received 15 chemical applications from various companies late last year but there has been no progress on having these chemicals registered.”
Fryer said the chemicals could not be used unless they were registered.
He added that some of the chemicals had proved to be effective through tests in America but the registrar had not processed the application.
Msunduzi municipal spokesperson Thobeka Mafumbatha said the municipal environmental department is unaware of the beetle.
“The information has not reached us yet. To date the PSHB has not yet been tabled for discussions in previous meetings,” said Mafumbatha.
“Now that the issue has been put before us, interactions with other organs of state will be made to discuss a way forward in dealing with the problem as soon as possible. The Msunduzi Municipality does prioritise the conservation of indigenous trees as they form part of biodiversity.
“Msunduzi is in a planning stage to replace the trees along the roads, most of which are Jacaranda trees (invasive), with indigenous, as we are passionate about conserving our indigenous environment.”
Arborists working on treatments
Fryer said although there is no registered chemical to treat the borer, he said Tree Treatment works with local arborists who individually have their own treatment protocols.
“While we don’t prescribe treatment, we do fully disclose the results of international research and trials,” said Fryer.
“Each arborist we work with has attended the PSHB training workshop, and I consider them to be ethical both in their pricing and their service offering.
“The two arborists we work with in Johannesburg are treating PSHB using local products [a full spectrum treatment protocol ranging from natural oils, bio stimulants, and traditional systemics pesticides] wherever possible, using tree injection.”
He said they do not use other methods like soil drench or foliar spray of poisons.
“Arborists in KZN and on the Garden Route are still evaluating their own treatment regimes and have not yet started offering treatments commercially,” he said.
“We have partnered with an arborist in Stellenbosch who is working closely with the various stakeholders on the ground in Somerset West.”
Habitat loss will have significant consequences
According to Fryer, although the loss of individual trees can be serious, a loss of habitat would have more significant consequences such as loss of overhead tree cover, shade, and wildlife that feed or live off the trees.
He said the consequences of habitat loss are most serious in highly stable habitats like forests, which KZN has plenty of. Fryer added that trees in urban areas will need to be replaced over the years as elimination of the beetle is “not possible”.
However, there are ways to try and treat the infected trees.
A Pietermaritzburg tree feller who asked not to be named said he had been to several properties around Pietermaritzburg where he had come into contact with the beetle.
“I have had to deal with a few problem trees that were killed by the borer. It is a very serious issue and I have heard quite a number of people complain about it.”
According to Tree Treatment and PSHB.org.za local municipalities should:
• Train staff to recognise and cut down heavily infested reproductive host trees from streets and public areas. • Infested branches can be cut if the main stem is not infested but this is unlikely. • Designate dedicated dumping sites where infested wood can be dumped as it poses a risk of spreading the beetle. • Chip wood to pieces finer than 2 cm at the dumping sites. • Provide a help desk (preferably online) where the public can report infested trees and get information.
How to spot an infected tree
• Borer holes the size of a toothpick on the trunk or branches.
• Entrance holes with or without white wood powder (frass) — usually in the cracks of thick bark like on old oak trees.
• Compacted frass (fine powdery refuse or fragile perforated wood produced by the activity of boring insects or the excrement of insect larvae) “noodles” begin emerging from entrance holes on the bark.
• Resinous or gelatinous drops oozing from entrance holes.
• Brown, watery sap begins staining the bark.
• When the bark is removed small dents in the sapwood, entrance holes, and/or fungal staining are visible.
• When the first 1-2 cm of sapwood is removed, beetle tunnels continue.
• The beetle is around two millimetres long. Mature females are very dark brown to black in colour and are larger than their male counterparts.
As a resident and tree owner you can:
• Try to determine whether the symptoms are really caused by PSHB.
• If unsure, ask for help from the municipality or your local arborist.
• If the tree is a heavily infested reproductive host, cut it down.
• Dump wood at a dedicated (by your municipality) dumping site.
• Chip the wood to finer than 2 cm, allow chips to compost by keeping it wet.
• Burn the wood on site (some beetles will fly away when the wood becomes hot or when smoke appears, so do not burn in uninfested areas)
• Do not move firewood around, especially not out of an infested area.
• Leave the wood in full sun under sealed clear plastic sheets for at least one month in summer or several months during winter.
• No chemical product is registered (legal) to use on PSHB in South Africa.
These are some of the trees affected:
• Forest bushwillow • Coast coral tree • Cape willow
• Blackwood • Black wattle • Coast coral tree
• Cape willow • Avocado • London plane
• Castor bean • White willow • Cape chestnut
• Pecan nut • Lemon • Cabbage tree
• Orange • Monkey plum • Aloe coral tree
• Cape ash • River red gum • Common fig
• Natal fig • Jacaranda • Macadamia nut
• Syringa • Mulberry • Wild olive
• Frangipani • Black plum • Peach
• Red stinkwood • Guava • Pepper tree
• Tree Fuschia