What was it all about?

Avocado orchards in south western Australia are vulnerable to attack by the six-spotted mite (SSM), Eotetranychus sexmaculatus. If left untreated, trees in infested orchards can be defoliated resulting in sunburnt, unmarketable fruit and reduced tree vigour. Miticides are available for use on the pest, but growers are aware of the potential for resistance to develop and are looking for alternative methods of crop protection.

This project, which ran from 2016 to early 2019, sought to assist growers in monitoring mite populations and implementing appropriate management techniques, as well as investigating the role that predatory mites could play during production.

Monitoring orchards for the pest is critical to avoid large populations building up. The team developed and distributed identification kits at talks about SSM to give growers the skills needed to identify the pest on avocado leaves. Until now, most growers had relied on consultants to monitor populations. The project team found the key time for the prevention of spring outbreaks of SSM is in late summer/early autumn or if no action taken, to monitor through winter.

Four species of predatory mites were assessed through releases in avocado orchards, but only one, Metaseiulus (Typhlodromus) occidentalis, reduced SSM in field studies.  

Field monitoring revealed other candidates for biocontrol. Large populations of the native Euseius elinae were found in orchards, even where potential predators had been released, as well as a previously unknown predator, Amblydromalus lailae. It seems likely that the two mite species work together to suppress six-spotted mite.  More work is required to quantify the role of A. lailae, either alone or in combination with E. elinae.

The project has considerably advanced the understanding of predatory mites as control for SSM, but more work is needed before predatory mites species either released or present naturally can be relied upon as a stand-alone method of protecting avocado trees from SSM.

ACT NOW

• Download the monitoring and identification guide for six-spotted mite.