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Ministry of Agriculture, Food and Rural Affairs

Woolly apple aphid (WAA)

Woolly apple aphid nymph Terminal infested with woolly apple aphid Woolly apple aphid infestation
Click to enlarge.

Beginner

Scientific Name
Erisoma lanigerum

Identification
Eggs:

  • Cinnamon-colored,
  • Oval shaped,
  • 0.3 mm in length.

Nymphs:

  •  0.6-1.3 mm in size,
  • Reddish brown or purple,
  • Often covered with a white waxy coating,
  • Pass through 4 instars.

Adults:

  • 3 mm long,
  • Aerial colonies are usually located at pruning cuts or the base of sprouts,
  • First observed in June on pruning cuts, around wounds of limbs and trunks and at the base of young shoots,
  • Infestations increase and spread to growing twigs and leaf axils of water sprouts.

Damage:

  • Feeding forms knots or galls on twigs or roots,
  • Excrete a sticky material called honeydew that drips on fruit and leaves; honeydew causes russet spots on the fruit, and a black, sooty fungus may establish.

Often Confused With

Period of Activity
Colonies of WAA can be observed at the end of tight cluster until mid-summer.

Scouting Notes
Look for characteristic cotton, waxy covering around pruning cuts, limbs and trunks and at the base of young shoots and water sprouts in the spring and mid to late summer.

Thresholds
There are no thresholds for woolly apple aphids. Consider management when infested twigs become swollen and galls form at feeding sites. Management is also necessary if colonies infest areas near fruit clusters or on young trees and nursery stocks. Damage is minimal when colonies remain on water sprouts and limbs away from the fruit clusters.

Advanced

Scientific Name
Erisoma lanigerum

Identification
Eggs: Cinnamon-colored, oval shaped and 0.3 mm in length.

Nymphs: 0.6-1.3 mm in size, reddish brown or purple and often covered with a white waxy coating. Nymphs pass through 4 instars. Like other aphids WAA have distinct cornicles on the rear of their abdomen.

Adults: Similar in appearance to nymphs but larger in size and may have wings or may be wingless.

Damage: Woolly apple aphid feeding forms knots or galls on twigs or roots. Galls are more visible on water sprouts than on tree wounds. Areas damaged by these aphids are more sensitive to frost and winter injury. Underground colonies also form galls on the roots. Aphid colonies feed on healing tissues of limb and trunks wounds, and where canker disease has established aphid feeding may spread the pathogen.

Woolly apple aphids excrete a sticky material called honeydew that drips on fruit and leaves. Honeydew causes russet spots on the fruit, and a black, sooty fungus may establish on the honeydew, downgrading fruit quality.

Often Confused With

Biology
There are many unanswered questions about the life history of woolly apple aphids. It was believed they overwinter only on elm trees as immature nymphs or eggs, with mature winged adults moving into orchards during the spring and summer. Recently, it was determined they can complete their lifecycle on apple, overwintering aerially or on roots. The aphids on elm are now considered to be a separate species called E. herioti (Börner) that can also develop on apple. The primary host of woolly apple aphid is unknown. 

Crawlers can move to roots any time they are active, mainly in June and July, and in the fall. There are winged aphids, and crawlers, and both move from tree to tree. Close tree spacing, and clean, smooth soil surfaces favour crawler migration. High soil temperatures, weed cover and distant tree spacing inhibit aphid movement between trees.

Research shows the frequency of infestation in orchards is correlated with orchard age. Orchards 25 years or older may have 70% to 100% tree infestation, with severity of tree infestation from 24% to 50% on each tree. Malling Merton (MM) series rootstocks are bred for resistance to woolly apple aphid, however some reports suggest this resistance may be breaking down.

Period of Activity
Colonies of woolly apple aphid can be observed at the end of tight cluster until mid-summer.

Scouting Notes
Look for characteristic cotton, waxy covering around pruning cuts, limbs and trunks  and at the base of young shoots and water sprouts in the spring and mid to late summer. 

Thresholds
There are no thresholds for woolly apple aphids. Consider management when infested twigs become swollen and galls form at feeding sites. Management is also necessary if colonies infest areas near fruit clusters or on young trees and nursery stocks. Damage is minimal when colonies remain on water sprouts and limbs away from the fruit clusters.

Management Notes

  • In organic orchards, and orchards minimizing use of broad-spectrum insecticides, allows natural enemies to manage woolly apple aphids.
  • Important natural enemies of WAA include Aphelinus mali (Haldemann), lacewing larvae, lady beetles and syrphid fly larvae.
  • Orchard management can impact woolly apple aphid populations.
  • Remove suckers at the base of the tree trunk to create less favourable conditions for establishment of these aphids.  Early generations developing on suckers migrate up into trees.
  • Remove suckers and water sprouts on major scaffold limbs – these are preferred sites of aphids. Hand suckering early in the season (June) improves spray coverage inside the tree.
  • Paint large pruning cuts with commercial pruning paint to discourage aphid colonies.
  • Summer prune in August to remove larger developed colonies.
  • Plant resistant rootstock such as MM.106 and MM.111 – bred to be resistant to woolly apple aphid. 
  • When necessary, early summer chemical management is better than late summer controls. Use high volumes of water to improve coverage and efficacy of insecticides.
  • Chemical management is also better when nymphs are young and colonies start to form – as pesticides are able to penetrate the waxy coating protecting aphids. See OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :