Trees and their care - current threat to our trees from the Shot Hole Borer Beetle

16 Nov 2018

The FWG Gardening Club met for a presentation from Charles Verster on the care and treatment of pests in our trees and about the current major threat to Johannesburg trees from the POLYPHAGOUS SHOT HOLE BORER BEETLE (PSHB)

The FWG Gardening Club met for a presentation from Charles Verster on the care and treatment of pests in our trees and about the current major threat to Johannesburg trees from the POLYPHAGOUS SHOT HOLE BORER BEETLE (PSHB)

Charles is a vegetation management specialist, a horticulturalist offering services in the maintenance of vegetation along railway lines, airports, power stations and commercial and residential estates, rehabilitation and revegetation of disturbed vegetation to return the environment to a natural state. He relocates plants, trees and succulents all over South Africa. He is also a horticultural facilitator, assessor and moderator ; teaching courses such as tree identification, Pest control operators etc.

We learned that trees have natural defences against pests, e.g. secretory cavities (where secretions are stored to repel pest insects or mites – lemon and bottle brush leaves are examples and can be rubbed on human skin as a natural remedy to prevent mosquito attacks).

There are 3 main reasons trees get attacked by pests:

  1. Alien, exotic pests. There are no local natural enemies, for example the Shot Hole Borer beetle.
  2. Poor biodiversity – where the natural balance does not exist e.g. where a small tree is planted in an atrium and no natural enemies are present.
  3. Stress – caused by e.g. drought, heat, flooding, fire, frost, strangled roots.

The Shot Hole Borer beetle comes from South East Asia, imported to South Africa possibly by ships in wooden pallets inhabited by the pest. It is a tiny beetle 2mm long and can fly short distances to host trees, where it breeds and literally bores cavities throughout the tree. It carries a fungus which it inoculates the wood for a source of food and this fungus is what kills the tree. There are probably more than 600 species of wood borer beetles worldwide, most attack dead wood but approximately 20 attack live wood. It has caused extensive damage around the world – and has arrived in South Africa some time in the last decade.

Stressed trees have a higher chance of infestation by PSHB, it is therefore advantageous to maintain your trees in a healthy state.

It has been found around the Ports such as Richards Bay. Once infected there is no tried and tested remedy as yet. There are ongoing trials to find solutions to this challenge.

Infected trees must be destroyed by burning or chipping for composting.

The trees most likely to attract this pest

  1. Host trees in which both the beatles and the fungus establish, and where the beetle successfully reproduce. In most cases the reproductive hosts will eventually be killed by the fungus.
  2. Host trees that are attacked by the beetle and where the fungus establishes, but where the beetle does not successfully breed. The fungus might, or might not cause disease and kill the trees.

What to look for in your trees is gum/sap/white powder/fine saw dust/stains from small holes in the bark. Another symptom is if part of the tree appears leafless, dead branches, die-back of trees or branches. To further investigate, take a knife and expose the area of the hole if an area around the 1mm diameter hole is discoloured, this may be a sign of infection by PSHB. Seek advice from a professional in your area.

For advice and assistance call Charles on 082 653 6081 or email to: charles@ulwando.co.za The occurrence of PSHB can also be reported via the APP , this will aid in the research and study into the future.

Reference

https://www.fabinet.up.ac.za/index.php/research/7

Paap T, de Beer ZW, Migliorini D, Nel W, Wingfield MJ. (2018) The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South

Africa. Australasian Plant Pathology 10.1007/s13313-018-0545-0 De Beer ZW. (2018) A tiny beetle and its deadly fungus is threatening South Africa’s trees. The Conversation (27 February) http://bit.ly/2F0J2Ln

Written by Francesca Beattie