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Aphid: Woolly apple aphid (WAA)

Eriosoma lanigerum


WAA is a reddish brown aphid covered with a white wax mass produced by specialized dermal glands. This wax mass gives the insect its characteristic woolly appearance. WAA have a complex life cycle that can involve overwintering either on apple or elm. Once on apple they move to feeding sites on roots or above ground. Root feeding produces knotty galls, and extensive feeding severly taxes the root system. Unfortunately, the above-ground WAA population is not a reliable indication of the root-feeding population. Above ground, crawlers settle in bark crevices, pruning cuts, wounds, leaf axils, and occasionally the stem or calyx of fruit. Black sooty mold fungus can develop on WAA honeydew.


  • WAA overwinter as eggs on elm trees. In early spring, wingless females remain feeding on elm for 2 generations. Winged females are then produced and migrate to apple trees late in June.
  • Once on apple, 'crawlers' are produced that spread throughout the tree. Several generations are produced on apples each summer. Large nymphs have a purplish body, concealed by tufts of "wool", which are actually fine wax strands.
  • In the fall, winged forms are again produced that migrate back to elm and deposit overwintering eggs.
  • Colonies can persist on apple roots throughout the year.


  • Monitor for WAA in mid-late summer when, if present, colonies of nymphs or adults become most visible.
  • Because of poor coorelation of above and below ground populations, there is only a tentative treatment threshold of 50% of pruning wounds.  Sample 10 possible infestation sites per tree on at least 10 trees per block.
  • Should WAA infestations appear on substantial numbers of leaf axils of terminals or fruiting spurs, treatment may be warranted to reduce possible injury to developing buds.


  • WAA are resistant to many commonly used insecticides. Apply an effective insecticide in summer if warranted.
  • Best control is obtained when insecticide is applied in July when small WAA colonies appear on periphery of canopy, but this is before colonies are easily visible.
  • Some insecticides can be applied to soil to manage WAA infesting roots.