The Western Australian Department of Primary Industries and Regional Development (DPIRD) led a biosecurity incident response to the detection of Pseudomonas syringae pv. actinidiae biovar 3 (Psa) in an establishing kiwifruit orchard in Western Australia (WA) during 2023-2024. Psa is a highly destructive bacterial disease that causes a significant reduction in yield and quality of kiwifruit. It is present in many kiwifruit production areas globally. In Australia, Psa is found in Victoria and New South Wales, and is a declared pest for WA. The objective of the response was to minimize negative impacts on the WA kiwifruit industry.
Following detection, extensive surveillance identified four infected premises including the original kiwifruit orchard and commercial and retail nurseries in the greater Manjimup and Perth metropolitan regions. The detection in retail nurseries indicated it may have been distributed extensively throughout WA residential backyards. Tracing efforts could not definitively assign the introduction of Psa to a single source or timeline. Plant and pollen imports were considered as the most likely pathways of entry.
Psa was assessed to be not technically feasible to eradicate. Psa is a systemic disease, located in all plant parts except fruit, can be latent and asymptomatic. The bacterium survives on fallen leaves and woody debris for up to six months, and can be spread by heavy rainfall, strong winds, mechanical transmission such as grafting, and by animals. Eradication would require complete destruction and removal of infected plants surrounded by a buffer zone of healthy plants. Psa can be managed, but not eradicated in other commercial production regions, and extensive destruction of plants would devastate commercial growers in WA.
Several challenges were encountered during the response. Kiwifruit growers were without an industry representative organisation within WA. There is no mechanism for a cost-sharing for eradication of a declared pest present in other parts of Australia. The Psa diagnostic protocol required lab validation, a process hampered by staffing and logistical constraints, exacerbated during the Christmas holiday period. Some industry members believed that a less virulent biovar was present in WA, rather than the highly virulent biovar 3. Furthermore, hot, dry weather and ongoing chemical applications limited the ability to detect Psa in symptomatic and asymptomatic samples.
These challenges were addressed through efficient and strategic deployment of the limited resources available and regular communication and engagement with industry. During this response, the formation of the Western Australia Kiwifruit Grower Association (WAKGA) was initiated, building and strengthening the industry. DPIRD facilitated the approval for emergency use permits for chemicals to manage Psa. Growers were trained on the biology, control and taxonomy of Psa and the biosecurity response process. Regular online meetings between DPIRD, industry and experts discussed the feasibility and desirability of eradication.
DPIRD supported the industry’s recovery while transitioning to management during 2024 by undertaking testing for Psa in kiwifruit plants and delivering grower educational opportunities with an international kiwifruit expert. This response has highlighted how industry and government relationships can improve, and industry can be strengthened when responding to biosecurity incidences.