Monitoring giant willow aphid (<i>Tuberolachnus salignus</i>) on apple trees in close proximity to infested willows

Abstract


 
 
 The giant willow aphid, was first found in New Zealand in 2013 and is now established throughout the country. An orchardist in the Tasman district reported infestation of his commercial block of young ‘Envy’ apple trees after harvest in May 2016, adjacent to two large willow trees heavily infested with giant willow aphid. Regular observations commenced soon after to determine seasonal activity, apple tree infestation, timing and impact and any alternative host plants or possible natural enemies. Key observations since are that the giant willow aphids appear in late September on willow shoots near the base of the tree reaching low numbers before disappearing again in late November. At this time, a ladybird species (Adalia bipunctata), where observed in the willows and on other plants nearby. In late December the aphids reappeared on the willows and numbers built to a peak in late February and remained on the willows until leaf fall. The aphids were not seen on the apple trees in any signi cant numbers until February when infestation and feeding continued until late autumn. After two seasons of infestation, the apple trees closest to the infested willows are now visibly ‘sick’ with yellowing leaves, stunted growth, reduced fruit production and branches blackened with sooty mould.