Six-spotted mite and its predators on sprayed and unsprayed ‘Hass’ avocado trees

ABSTRACT

Six-spotted mite, Eotetranychus sexmaculatus (Riley), is an introduced pest of ‘Hass’ avocados in New Zealand. Avocado orchards were surveyed for six-spotted mite and its natural enemies during 2016–18. Mean counts of six-spotted mite differed when compared by year. For each year, the effect of not spraying or spraying according to an integrated pest management programme (AvoGreen®) was not consistent for most location and season combinations. When year was ignored and all locations considered together, the leaves of unsprayed trees had fewer six-spotted mites than those of sprayed trees during autumn/winter. The phenology of mites and their predators in relation to leaf abscission was also determined on unsprayed potted trees during 2018–20 at two sites. Defoliation occurred in October and November each year but the association with densities of six-spotted mites was not consistent. Four species of phytoseiid mite predators were identified on orchards and potted trees with the most common species being Amblyseius herbicolus. The coccinellid mite predators Stethorus bifidus and S. histrio occurred on potted trees. The evidence that predators were able to control six-spotted mite populations was somewhat equivocal. Trials comparing sprayed and unsprayed trees under the same nutrient management and during multiple seasons would be useful.

KEYWORDS:

• Mites
• pest
• predation
• Tetranychidae
• Phytoseiidae
• Stethorus
• Persea
• fruit
• orchard

Acknowledgements

Thanks to Dr Zhi-Qiang Zhang for identification of the phytoseiid mites collected from avocado leaves, to Clare Schatzdorfer and Val Baker for identifying orchard blocks and arranging for leaves to be sampled, to Peter Wright and Glen Clark of the Pukekohe Research Centre for their support in maintaining potted avocado trees, and to Glenys Parton and Catherine Wilks of Avocados New Zealand for industry and spray diary data.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Funding was from the Plant & Food Research Strategic Science Investment Fund project on avocado pest ecology (2016–20).