PSHB POMEWEST
PSHB
and its research investigation
Western Australia
Euwallacea fornicatus, also known as Polyphagous shot-hole borer (PSHB), is a tiny beetle that bores into living trees, causing damage and dieback. It tunnels into the tree's stems and branches and spreads with the movement of infested trees, firewood, and green waste material.
Words Dr Duccio Migliorini and Shahidul Khan, Harry Butler Institute, Murdoch University
THE beetles have a symbiotic relationship with a fungal organism from the genus Fusarium which is used as a food source for the beetle and its larvae. The fungus is inoculated by the adult beetles during galleries excavation phases, and it colonises the vascular tissue of susceptible trees. It is the beetle and fungus complex (PSHB-Fusarium Dieback “PSHB-FD”), not the beetle alone, that causes the damage. Symptoms include wilting and dieback of tree branches and leaves, often starting in the upper canopy. PSHB-FD affects hundreds of host species globally from horticulture species (including avocado, mango, stone fruit and citrus) to native Australian species and introduced, ornamental tree species.
Situation in Western Australia
PSHB was first reported in Western Australia in 2021 from a boxelder tree in Fremantle. Its current range is Perth urban and peri-urban area, where it spread on native and ornamental woody plant species. Presence of PSHB colonization in crop plantations was detected only once on avocado trees. Government-led tree removal is now limited to high-risk containment areas, where landowners are now responsible for managing infested trees in most metro areas.
Left: Sapwood lesions on Excised stems of Prunus domestica caused by artificial inoculation of the PSHB associated Fusarium. Right: Fungal inoculation of a pear excised stem using toothpicks previously colonized by PSHB associated Fusarium.
POMEWEST PSHB
Research project
The Harry Butler Institute at Murdoch University is conducting a major research project funded by the WA Agricultural Research Collaboration (WAARC) to improve our understanding of the interactions between PSHB-FD and its host plants in the Western Australian environment, and to identify effective management strategies.
The project is being conducted by a multidisciplinary team of plant pathologists and entomologists.
Dr Duccio Migliorini has travelled to various WA orchards to collect commercial rootstock and plant material samples to assess susceptibility to the Fusarium fungus.
Early results have shown that the major stone fruit cultivars grown in Western Australia differ in their sapwood reaction to the fungal pathogen. Laboratory trials showed that three weeks after inoculation, some nectarine and plum cultivars developed, on average, slightly larger lesions than the other stone fruit cultivars tested, including pear and some apples. Over the coming months, these trials will be expanded to include additional plant species of economic, ornamental and ecological importance in WA.
Developing artificial pheromone lures
Research on the beetle is being conducted through several experimental laboratory trials and aims to fill knowledge gaps regarding the insect's biology and chemical ecology.
Five artificial diets for colony establishment in the laboratory were successfully selected, allowing investigation of beetle reproductive performance. To identify potential attractants for lure development, an experimental olfactometer was used to test beetle preferences to different volatile sources. Notably, significant attraction was observed towards multiple source types tested. These findings demonstrate the feasibility of maintaining PSHB colonies on artificial diets and identify promising volatile sources for future volatile organic compound (VOC) characterisation and lure-trap testing with novel attractants.
Limited chemical options
Chemical control strategies evaluated in South Africa and California have consistently involved trade-offs that limit their practical application.
In brief, contact insecticides (e.g. Bifenthrin) target adult beetles immediately before dispersal or shortly after they land on a host tree, making them effective only during periods of active beetle flight. Systemic sapwood insecticides rely on uptake through the vascular system and accumulate in the sap. However, because PSHB does not feed on sap, their effectiveness is limited.
The combination of Emamectin benzoate (insecticide) and Propiconazole (fungicide) by trunk injection is currently considered the most effective treatment for high-value ornamental trees. However, both compounds are only locally systemic, meaning they move slowly through vascular tissues and require repeated applications to maintain efficacy.
Furthermore, as observed with other systemic fungicides such as phosphites, these products cannot be effectively applied to heavily infested trees because the vascular system is already severely compromised, preventing the chemicals from reaching all parts of the plant.
To identify the most effective chemical control strategy, our project includes a large-scale field experiment designed to compare the efficacy of several combinations of state-registered insecticides and fungicides for the management of PSHB-FD in infested trees. The trial is being conducted on native tree species in a wetland severely affected by the disease and is well underway.
Containing PSHB-FD is a major challenge, as demonstrated by experiences in South Africa and California over the past decade. Nevertheless, there are realistic prospects that an effective integrated management protocol can be developed by combining multiple control strategies, such as chemical treatments and sanitary pruning.
The role of research is to identify the most informative and effective scientific components and translate this knowledge into practical, evidence-based protocols for growers and land managers.
The strong interest shown by industry stakeholders in WA over recent years is therefore highly encouraging and provides a solid foundation for the development and implementation of effective control strategies.
Duccio will be presenting the project findings so far at the Pomewest Grower Dinners from 1–3 September 2026. 🍐
More information
This project is funded by the WA Agricultural Research Collaboration in partnership with Murdoch University Harry Butler Institute, the WA Department of Primary Industries and Regional Development, University of Western Australia, Curtin University and Arbor Carbon.
Duccio Migliorini, Harry Butler Institute Murdoch University, Duccio.Migliorini@murdoch.edu.au