Earlyseason use of insecticides for management of woolly apple aphid (<i>Eriosoma lanigerum</i>) in Nelson apple orchards

Abstract

A spray strategy to control woolly apple aphid (Eriosoma lanigerum WAA) was assessed on apple orchards in Nelson Carbaryl applied for fruit thinning was either sprayed alone or combined with diazinon on Braeburn apples at four orchard sites infested with WAA The diazinon plus carbaryl treatment reduced WAA levels and there were lower numbers of WAAinfested shoots with considerably fewer colonies on branches and shoots in November Numbers of WAA colonies on shoots in January were 50 lower overall in the diazinon plus carbaryl treatment There was an initial decline in numbers of the WAA parasitoid Aphelinus mali in both treatments but they increased steadily during the season and high levels of parasitism were evident by harvest The parasitoid was able to suppress the lower populations of WAA in the diazinon plus carbaryl treatment and this resulted in significantly lower levels of WAA shoot and fruit infestation and bud damage in late March

Toxicity of pesticides to <i>Aphelinus mali</i> the parasitoid of woolly apple aphid

“…Carbaryl is used early in the season for fruit thinning and, especially on varieties like 'Braeburn', may need to be applied twice to achieve the ideal crop load. This use pattern can be particularly disruptive to WAA biological control and has led to a strategy of applying diazinon at the same time as carbaryl to minimise WAA outbreaks later in the season (Shaw & Wallis 2009). The present study has demonstrated that diazinon residues decay relatively quickly, which helps explain why judicious use of this product mid-season can provide good effective control of WAA without depleting A. mali populations too much.…”