Disease management in macadamia (MC07003)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

This project MC07003 - disease management in macadamia provided significant science-based outcomes for the Australian Macadamia Industry. Firstly, it provided effective management strategies for two major diseases - husk spot and Phytophthora stem canker/tree decline in macadamia. Secondly, it improved the understanding of the causal agent and the epidemiology of several emerging disease-systems such as husk rot and tree dieback. This knowledge underpinned the development of control measures for these diseases. Thirdly, it highlighted new pathogens and diseases of macadamias in Australia and overseas.

This project generated additional data that enabled successful registration of a new product (Cabrio®) for husk spot control by APVMA. The researcher identified three new potential fungicides for future field assessment from laboratory screenings of several new fungicide products with softer chemistries and more environmentally suitable properties. These products may have been suitable as a replacement of carbendazim. The project provided tools for screening and selection of husk spot resistance in the macadamia breeding program. The project provided results of laboratory and field trials of biological products for husk spot control. The researcher developed simple-to-use risk assessment tools to aid growers’ decision for husk spot control and identified management practice that were vital to avert severe economic loss due to husk spot.

In addition to providing a clear understanding of the pathogen that caused stem canker and tree decline in macadamia orchards, MC07003 provided management strategy using phosphorus acid and metalaxyl to control Phytophthora-induced diseases. It developed a disease assessment tool and decision guide for application of phosphite to control Phytophthora control. It provided vital information that underpinned the need to develop or adopt a nursery certification scheme for macadamia and facilitated two industry workshops to promote the benefit of a certification scheme to plant health.

The project showed that the fungi associated with macadamia dieback belonged to the family Botryosphaeriaceae and its severity over time may have shifted its importance from minor to major disease of macadamias. The project showed that sudden death syndrome followed the onset of severe stress and the combinations of the stress factors together with the biological pressure from pathogens and pests favour the development of sudden death syndrome causing tree death.

Future R&D needed to evaluate the new products in field trials and provide the economic thresholds for biological control options for husk spot. A comprehensive integrated disease management strategy including the use of risk assessment and disease forecasting tools, cultivar resistance, biological and cultural control practices such as removal of sticktights from tree canopy for husk spot needed to be evaluated. Improved understanding of relationship of soil health-organic matter and Phytophthora-induced diseases was needed for sustainable management of the diseases. Good understanding of each disease system in macadamia was required.