A recent joint study by Stellenbosch University and the University of Pretoria found that the polyphagous shot hole borer beetle could lead to the removal of 65 million urban trees by 2030 if nothing is done to stop its spread.
POLYPHAGOUS SHOT HOLE BORER BEETLE PRESENT IN EIGHT PROVINCES
The shot hole borer was first detected in South Africa Durban in 2012 and since then it has spread to eight out of nine provinces, Limpopo being the exception. It is believed that the invasive species entered the country via a container ship.
It is the largest current outbreak of the pest. According to Stellenbosch University, this invasive species is different to what the country is accustomed to because it will have the largest impact on trees in urban areas.
The shot hole borer can only fly short distances – between 500m and 2km. Its rapid spread through the country is thought to be the result of people moving wood across province borders.
The beetle carries a fungus (Fusarium euwallaceae), which it feeds on. The same fungus infects trees and leads to their death.
Research is underway to find a biological control agent for this fungus and the shot hole borer. However, such an agent is at least a decade away from being found. It will be even longer before the agent could significantly reduce the beetle’s spread.
THOUSANDS OF TREES AT RISK
The article – An assessment of the potential economic impacts of the invasive polyphagous shot hole borer (Coleoptera Curculionidae) in South Africa – was published in the Journal of Economic Entomology this week.
One of its co-authors, Professor Francois Roets, said a tree-rich town like Stellenbosch could lose 20 000 of the old oak trees that line its streets, while Somerset West – where the beetle was detected four years ago – already has more than 10 000 infected trees, some of which are now dying.
Urban trees are more susceptible to the beetle and its fungus because these trees are already under stress due to the urban environment – compared to trees in a rich natural environment.
Roets added that people in urban environments tend to plant cloned non-native tree species that are not as capable of fighting off novel pests.
Overall, the potential economic impact of the shot hole borer between 2020 and 2030 is R275 million, if business continues as usual.
The main author of the article, Professor Martin de Wit municipalities across the country will have to remove and dispose of an estimated 65 million trees during that period.
“We need a national policy and coordinated strategy for municipalities to stop this beetle in its tracks,” said de Wit.
“To date, the polyphagous shot hole borer is not yet listed under the Alien and Invasives Species Regulations, making it difficult for municipalities to react effectively,” he added.
There is no tested and approved insecticide or fungicide registered in the country to treat infestations of the shot hole borer effectively for urban trees.
Professor Roets said, “Anyone who tells you they will save your tree with chemicals and fungicides is likely lying and will be breaking the law.”
The Democratic Alliance (DA) called on the Minister of Environment, Forestry and Fisheries (DFFE) to advise how the national government plans to assist with a coordinated response to the shot hole borer threat.
Dave Bryant, the opposition’s shadow environment minister, said the country’s fragile economy “simply cannot handle such a devastating loss” and wants an emergency meeting with all spheres of government to be convened to plan a way forward.
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