Andrew Taylor of DPIRD spoke about apple scab and fungicide resistance at the recent Apple and Pear IPDM field day in Manjimup, Western Australia.  Andrew, in collaboration with Curtin University, recently completed a project that collected scab samples from a number of orchards in various apple growing areas around the state, and tested each isolate for resistance against all registered fungicides.

They found that apple scab is established in Western Australia, particularly in the Perth Hills.  All registered fungicides for apple scab provide effective control at a field level in Western Australia. However, amino-acid mutations were found in some isolates. These mutations can be the precursors to the development of fungicide resistance and loss of efficacy in the field. The scab isolates collected as part of the project are lodged in the WA fungal culture collection as a population baseline. If field failures occur in the future, isolates can be compared to those from this project to determine if resistance has developed and is responsible for the control failure.

Even though growers should currently have no concern in the efficacy of registered products, there are a number of things to keep in mind for current and future management.

• Apple scab is a high-risk pathogen for developing fungicide resistance.
• The Western Australian apple scab population is highly variable which increases the risk of resistance developing in the future.
• Apple scab is not evenly found across all apple growing areas in Western Australia. On-farm biosecurity and hygiene is important to prevent the spread to new properties and contain its spread within orchards.
• All growers need to be vigilant and monitor for scab lesions in spring, paying particular attention to new plantings as the pathogen can survive in bud material of dormant wood. New growth is highly susceptible to infection.
• The Croplife Australia website (https://www.croplife.org.au) has the current fungicide resistance management guidelines for apple scab and these should be followed to reduce resistance risk.
• Further investigations are required into the population structure of inaequalis in Western Australia and how this relates to eastern states population, impact on disease management and cultivar breeding.

The project was funded by the WA APC Pomewest subcommittee. A final report of the project is available from Pomewest: www.pomewest.net.au.

Article reviewed by David Williams (Agriculture Victoria)