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Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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?

Diseases of avocado continued to be identified by industry as a key factor limiting productivity in most of the major production zones. Beyond the farm gate, postharvest diseases also accounted for significant losses in the supply chain. This project investigated options for more sustainable management of major root- and fruit-infecting diseases. A focus of the research was to reduce fungicide inputs, for the benefit of the environment and general public.

• Rootstock material with superior establishment and survival capacity under very high Phytophthora root rot pressure in the field was identified. Two new selections were better able to withstand the disease than most of the commercial cultivars used in the industry today. The yield and fruit quality performance of these rootstocks was being assessed in a separate project at the time, and potential for commercialisation and release to industry was under discussion
• Application rates and timing of potassium phosphonate for Phytophthora root rot management were optimised. The rate for foliar treatment was increased, and adopted by industry. Injection application had to be be performed at a time when fruit was not an active metabolic ‘sink’. Later-maturing fruit varieties such as ‘Reed’ required delayed injection so that phosphonate did not accumulate in developing fruit and residues in fruit were not excessive
• Preliminary trials indicated the potential of some alternative approaches or products for reducing postharvest disease in fruit. While some of these products were fungicides used in other horticultural industries, others had no pesticidal mode of action and relied on boosting calcium levels in peel or activating plant defences to limit the infection by fungi and development of disease symptoms. Further trials were necessary before recommendations could be made to industry
• Brown root rot had been identified as limiting productivity in avocados in some production areas. This fungus killed trees, and the only practical management option at this stage was tree removal. Further research was needed to evaluate chemical and cultural options for minimising the impact of this disease to growers and industry.