Background/context:

Husk spot caused by the fungus Pseudocercospora macadamiae is a serious disease of macadamias in Australia. It may result in premature nut drop giving rise to nuts with low kernel oil content that cause significant economic losses. In order to effectively control husk spot in a sustainable manner, disease management strategies need to be based upon a better understanding of the disease cycle of the pathogen. At the same time, effective chemical control options based on scientific principles need to be put in place and alternative control strategies investigated. The choice of cultivars for new plantings needs to be based on agronomic characters and resistance to pest and disease, including husk spot.

 Aim:

The project aimed to increase yield and kernel quality through effective control of husk spot, to reduce and more effectively use fungicide through a better understanding of the infection process as this will lead to more targeted spray regime, to introduce more sustainable disease control practices involving the targeted use of defence promotors or strobilurins, to provide accurate assessments of disease resistance in cultivars to aid in the establishment of orchards with higher level of husk spot resistance, and to enable effective selection for husk spot resistance in the breeding program to give rise to more resistant cultivars in the long term.

Major Outcomes:

Following extensive 2-years field and laboratory trials, we have been able to show that:

• Yield-limiting infection occurs at match head stage of the developing nuts

• Infection is mainly via the stomata which may influence resistance

• Applying Spin and Copper sprays at match head stage is more effective than starting later.

• Infected stick tights are an effective source of inoculum between seasons

• Disease impact varies between varieties and depends on time of infection

• An effective Strobilurin compound was identified and may serve as an alternative to Carbendazim

After communicating these initial findings on timing of application to industry in 2005, growers that have modified their chemical practices as suggested have not observed significant losses due to the disease. This project is funded by HAL and will continue beyond the life of the CRCTPP.

For more information contact:

Dr André Drenth
Department of Primary Industries and Fisheries
Phone: +61 (0)7 3896 9345
Email: mailto:Andre.Drenth@dpi.qld.gov.au