Many unanswered questions bugging the arbour industry

The alien invasive polyphagous shot-hole borer beetle, with its deadly fungus Fusarium euwallaceae, has created widespread havoc in South Africa. As multiple research teams study the insect, it is clear there is no single solution to deter it. Magda du Toit recently joined a media information session hosted by Hortgro, during which various aspects of a research project under the auspices of Stellenbosch University were discussed, with visits to trials in the pear orchards at Lourensford Estate in the Western Cape.

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Almost six years have passed since the detection of the polyphagous shot-hole borer (PSHB) (Euwallaceae fornicatus) in trees in South Africa, and it seems the beetle is spreading at a fast and steady pace. According to researchers, it can now be found in nearly all parts of South Africa and in more than 160 tree species.

The PSHB is native to Southeast Asia. This tiny beetle, only 1mm in diameter, attacks its host by tunnelling into trunks, stems, and branches.

According to scientists, this particular beetle is arguably the most damaging alien tree pest ever to arrive in South Africa.

The presence of PSHB was confirmed in 2017 based on the findings of Dr Trudy Paap of the Forestry and Agricultural Biotechnology Institute (FABI) of the University of Pretoria, who had identified PSHB on London plane trees in the Pietermaritzburg Botanical Garden in KwaZulu-Natal.

The spread of PSHB was subsequently confirmed in trees across the country, including in Johannesburg, Cape Town, Stellenbosch, Bloemfontein, Durban and Pietermaritzburg. It can be found in all provinces except Limpopo.

EXTENSIVE OUTBREAK

This widespread PSHB invasion in South Africa constitutes the largest geographical outbreak of the beetle in the world. It is affecting trees in all sectors: the agricultural and commercial forestry sector, urban trees (public spaces, streets, gardens), as well as native trees in natural forests.

According to Wanga Ncise, senior horticulturist at Stellenbosch University Botanical Garden, they recently confirmed three cases of PSHB prevalence in the botanical garden in Platanus acerifolia,