Ecology and management of the leafroller (Tortricidae) complex over ten years during establishment of an organic pipfruit orchard in Central Otago, New Zealand

Abstract

The ecology and management of leafroller pests (Tortricidae) in a newly-planted organic pipfruit orchard at the Clyde Research Centre, Central Otago, New Zealand were studied from 1991 to 2001. Adults were monitored with pheromone traps and fermented molasses bait traps, and immature stages and their damage by sampling vegetative shoots, fruit clusters, and harvested fruits. The dominant pest species was Epiphyas postvittana, followed by Planotortrix octo, and minor damage was caused by Ctenopseustis obliquana and Pyrgotis plagiatana. The major leafroller species are bivoltine in the region, with generations well synchronised. High damage (>30%) was expected under organic management but did not eventuate, with only 0.3–2.6% of harvested fruit being damaged on standard cultivars, which received regular fungicide sprays, with no trend of increasing damage over time. Disease-resistant cultivars, which received minimal or no fungicide sprays, suffered damage at harvest of 0.8–9.4%, which similarly did not increase over time. Population sampling from 1994 to 1998 indicated high larval mortality, including major parasitism by the braconid Dolichogenidia tasmanica, but with scope for further parasitoids known to be present in Otago but not yet present in this young orchard. The standard apple and pear cultivars ‘Fuji’ and ‘Taylor's Gold’ regularly suffered harvest damage >2%, which is a problem for exports to some markets. Sprays of Bacillus thuringiensis against the larvae of the first generation on these cultivars were only partially successful in protecting the crop. Strategies for improved management are discussed.