Management of six-spotted mite in WA avocado orchards – phase 2 (AV19002)

What was it all about?

This investment, which ran from 2019 to 2022, delivered effective options for the integrated pest management (IPM) of six-spotted mite in avocado orchards. The project developed an IPM guide for avocado growers and a series of videos to assist with accurate mite monitoring. The guide contains information on:

• When and how to monitor
• How to identify pest mites and beneficial arthropods
• How to improve your on-farm biosecurity
• A range of six-spotted mite management practices

To develop the guide, the research team investigated several different areas of monitoring and management, including:

• The taxonomy of the pest mite
• The development of a reliable and user-friendly monitoring program
• The potential role of predatory mites, both naturally occurring and mass-reared
• The relationship between tree nutrition, six-spotted mite and defoliation
• On-farm biosecurity and the spread of six-spotted mite
• Sustainable miticide use, including case studies of effective and ineffective management
• Alternative pesticide products

The project also collaborated with a researcher in New Zealand, the only other place in the world where the six-spotted mite is considered a pest of concern in avocados, to ensure the most up-to-date research and management practices for this pest in the world informed the management recommendations devised for Australian growers.

Long-term and intensive monitoring was conducted in over 24 orchard blocks over two years to determine seasonal trends and mite distribution patterns that were then used to develop a monitoring protocol. The research team also developed case studies of miticide and spray oil products for six-spotted mite control and management thresholds. The results showed that monitoring is essential to determine if management is necessary. Monitoring should be done fortnightly in autumn and spring, which are also the two times of the year when management with miticides is recommended if monitoring indicates six-spotted mite numbers above the ‘threshold’. A threshold of 40 per cent leaves infested in spring and 10 per cent infested in autumn was devised.

The case studies demonstrated the importance of monitoring and managing blocks separately, given the variability of six-spotted mite numbers between blocks. They also highlighted the importance of following label instructions and ensuring adequate spray coverage, as not doing so can lead to lower than expected levels of control.

Two studies investigated the relationship between leaf nitrogen, six-spotted mite and defoliation. Neither study provided clear indications of relationships that could lead to management recommendations.

The nitrogen trials, case studies and anecdotal evidence from both WA and New Zealand all indicate that other factors influence spring defoliation in avocado trees and that stressed trees are more likely to defoliate when six-spotted mite are present. These other factors likely include water stress, fruit load, level of flowering, pressure from other pests and diseases and general tree health. They need to be considered when deciding if and how to manage six-spotted mite.

The on-farm biosecurity survey and review of six-spotted mite spread concluded that six-spotted mite can spread naturally via aerial dispersal. However, human-aided spread is more targeted and has the potential to bring six-spotted mite into orchards more quickly and should be managed. To reduce the risk of six-spotted mite being spread between properties, the project recommended that machinery and equipment coming into orchards be clean and free of plant debris and that new planting stock be inspected for pests and controlled if needed.