What was it all about?

From 2017 to 2022, this project delivered a integrated disease management program to increase the productivity and profitability of macadamia growers and the Australian macadamia industry at large.

Working closely with the industry’s integrated pest management program, the work included a combination of research, training, and communication activities to improve management approaches and diagnostic capabilities for a range of priority diseases for the industry, including husk spot, Phomopsis husk rot, flower bright complex, Phytophthora root rot, and branch dieback.

The research generated new knowledge on the biology and ecology of endemic and emerging diseases in macadamia. It revealed that diseases in macadamia are complex and are caused by a suite of pathogens that interact with the environment leading to reduced productivity. Twelve known plant pathogenic species and 14 novel pathogens were identified for the first time and proven to cause diseases in macadamia. Prevalence of the pathogens varied with regions and climatic conditions. Novel assays were developed to test the aggressiveness of the pathogens and to examine susceptibility of macadamia cultivars. Significant differences in disease severity were observed among macadamia cultivars to husk rot, flower blight, Phytophthora root rot, and branch dieback. Fourteen genotypes of Macadamia tetraphylla and two M. integrifolia were identified as resistant to the two most aggressive species of Phytophthora in macadamia (P. cinnamomi and P. multivora). In flower blight disease systems, this project revealed significant variations in infection to the three types of flower blight (green mould, grey mould, and dry flower disease). Disease severity on macadamia flowers varied with the stage of flower development at the time of infection.

The project developed and evaluated disease control options including cultural practices and their use in an integrated system. A key component of disease control strategy developed is to reduce pathogen inoculum and enhance macadamia resilience to pathogen attack, whilst broadening the spectrum of disease control options available to growers. New crop protection products, which aligned with the industry Strategic Agrichemical Review Process were developed and the data generated in this project supported the registration of two products - Belanty® (mefentrifluconazole) and Merivon® (Fluxapyroxad and Pyraclostrobin) in macadamia.

The project revealed that diseases in macadamia are influenced by interactions of two or more intrinsic and extrinsic factors. Therefore, it is recommended that future R&D should build on the findings in this project to support the development of predictive tools and control options to managing multiple diseases in macadamia.

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A wide range of resources were developed and disseminated to macadamia growers to manage diseases. These include disease diagnostics, early detection, and predictive tools. Field guides and fact sheets with information on disease cycles and control options were provided as printed and digital materials.

The resources are available on the Australian Macadamia Society website.