This investment identified strategies to minimise the effects of critical diseases in avocado orchards and in avocado fruit as it progresses through the supply chain – helping the avocado industry increase orchard productivity and fruit quality.  

Challenge  

Poor tree health and sub-standard quality fruit are challenges facing avocado growers and the whole avocado industry. While diseases such as Phytophthora root rot, anthracnose and stem end rot have been problematic since the early days of the industry in Australia, other diseases have been more recently identified as economic constraints to productivity. This project was undertaken to learn more about the key diseases affecting avocados and to scientifically evaluate options for managing them on-farm.  

Response  

The research was conducted across several commercial orchards in the glasshouse and laboratory. The trial work demonstrated the efficacy of fungicides and other treatments in the targeted management of Phytophthora root rot, black root rot, Verticillium wilt, branch dieback, and fruit diseases anthracnose and stem end rot. Investigations into a worsening orchard problem, panicle dieback, have shown a role for Colletotrichum sp. fungi and that it could be managed by heavy pruning and fungicide sprays at flowering and early fruit set.  

Research within the project has raised concerns that key fungicides may no longer be effective in keeping fruit clean from fungal diseases; however, promising new candidates have been identified.  

Field trials with soil amendments and mulching have given variable results. Covering rows with black plastic before planting kept newly planted trees healthier for longer in a site with severe Phytophthora root rot pressure. Woodchip mulch treatment with gypsum and chicken manure improved the soil depth, and there were indications of increased yields with mulch compared with no mulch throughout the trials. Nutrient analyses in the fruit pulp showed that higher calcium, silicon, and lower nitrogen are sometimes (but not always) correlated with reduced severity of postharvest disease. Nutrient analyses of pulp and leaf also demonstrated an interesting correlation between high boron and reduced fruit yields. Fruit from Western Australian orchards have a high incidence of infection by Colletotrichum species, which are known to infect at cooler temperatures.  

Industry support, education, and extension activities have been critical components of the project.   

In addition to being published in the scientific literature, several grower-focused articles were published in Talking Avocados and Guacamole, and presentations were made to growers and other stakeholders at Avoskills workshops, industry forums, and two World Avocado Congresses.   

There has been considerable input into other printed extension material, such as posters, videos and the “Problem Solver Field Guide”. Responding to numerous grower enquiries and diagnostic work on samples were necessary, as correct diagnosis of a disease or other problems is required for optimal and cost-effective management strategies.  

Benefit  

This project’s activities have increased grower awareness of best practices and strategies to minimise the impact of avocado diseases and pathogens, aiming to improve fruit quality and maximise orchard productivity.  

Several of the project’s workshops surveyed the participants, who rated them as very useful or extremely useful and indicated that they intended to make changes because of the workshop, for example, more mulching, more foliar sprays, open up canopy, more strategic use of fungicides, more focus on crop quality, anthracnose control, and N:Ca monitoring.   

The project has also seen growers and packsheds revising fungicide use in light of the information provided on maximum residue limits, increased volumes of exported fruit, and the requirement for high-quality, disease-free fruit.