Main Club July 2023

Two presenters, Chelsea Payne from Botanic Gardens and Parks Authority (BGPA) and Dominic Castledine from the Department of Primary Industries and Regional Development (DPIRD), talked about an important pest currently threatening trees in Perth suburbs. Our president, Basman Al-Jalely, also contributed since that is one of his research areas.

The Polyphagous Shot-hole Borer (PSHB), Euwallacea fornicatus, is a beetle which bores into trees and can lead to their death. Originating in Southeast Asia, it has spread to several parts of the world and has recently been detected in Perth. The beetles, the size of a sesame seed, do not kill the tree directly but cultivate a fungus, a species of Fusarium, as a food source for the beetles and their larvae. The fungus destroys the vascular tissue, and this causes Fusarium dieback, which can kill the tree. The beetle and the fungus have co-evolved and are co-dependent.

Dominic said that Fusarium dieback if established here, would cause significant loss of canopy in urban streets and the loss of some types of fruit and nut trees and perhaps native vegetation. The full effect has yet to be known. The main symptom is the appearance of “shot holes” – circular holes only 1mm in diameter. Broken branches may show galleries, appearing as black lines in the wood. Some types of trees show frass or “wood noodles”, gumming (resin oozing), lesions, and “sugar volcanoes” on avocado trees.

In Western Australia (WA), there are 130 recorded hosts, half of which are reproductive hosts, in which the beetle can complete its life cycle. Current top hosts are Maple, Robinia, Coral Tree, Moreton Bay Fig, Plane, Poinciana, Mulberry and Coprosma. Some native hosts are Acacia saligna, Banksia littoralis, Corymbia calophylla and Eucalyptus camaldulensis. See www.agric.wa.gov.au/borer for a complete list. A code can be scanned from the website.

DPIRD is working to eradicate the pest by trapping, surveillance, inspections, managing infested trees and working with Greenwaste, and has established a quarantine area around Perth. Removal of the tree or proper pruning are very effective control method.

Chelsea talked to us about their work at Kings Park in biosecurity. BGPA is part of the International Plant Sentinel Network, an early warning system for Botanic Gardens. They also are part of a Plant Health Australia Surveillance program, which forewarned BGPA about PSHB. BGPA also has a Field Collection Program. Seeds of plants from all over the state are kept in a seed bank in case these species are wiped out by disease. They also do selective breeding and hybridisation for resistant plants.

We can help stop the spread by reporting any evidence of the borer, telling others about the PSHB, and not buying susceptible trees. We should prune trees to Australian standards, using natural target pruning, which is best left to qualified arborists. We should promote healthy trees and encourage local councils to maximise plant diversity. (Mallees and the Proteaceae are very suitable.)

Mike Gregson