Woolly apple aphid
Eriosoma lanigerum
1 host plant
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Woolly apple aphids are covered in distinctive white, waxy filaments that resemble wool or cotton. You will see white cottony masses on apple bark, particularly in crotches, pruning wounds, and graft unions. Affected areas develop galls and cankers. Honeydew attracts ants that farm the aphids. Most damaging on young trees and in warmer regions; damage is minimal in cool climates.
For young orchard trees, prune out heavily infested wood in late winter. Spray horticultural oil in late fall or early spring before buds break to smother overwintering aphids. For landscape apples, accept minor gall formation. Do not over-fertilize. Encourage natural enemies by avoiding broad-spectrum pesticides.
Quick Reference
Woolly apple aphid Emergence (est.) typically begins around 945 GDD₃₂. As of April 23, 2026, all seven Puget Sound stations have passed this threshold (1434.4–1592.7 GDD₃₂), so Emergence (est.) is likely underway across the lowlands.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 23, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,593 | Emergence (est.) | — | — |
| Seattle / UW | 1,554 | Emergence (est.) | — | — |
| Kent / Auburn | 1,537 | Emergence (est.) | — | — |
| Olympia / Tumwater | 1,505 | Emergence (est.) | — | — |
| Bellingham / Whatcom | 1,483 | Emergence (est.) | — | — |
| Tacoma / Puyallup | 1,472 | Emergence (est.) | — | — |
| Sequim / Rain Shadow | 1,434 | Emergence (est.) | — | — |
Source: Pest GDD Catalog, UMD IPMnet. Egg hatch for Eriosoma lanigerum (woolly apple aphid). Added 2026-04-03. About GDD₃₂ →
Adult woolly apple aphids are reddish to purple and are completely covered with thick, woolly white wax. The insects feed on roots, trunks, limbs, and shoots, producing galls at the site of the infestation. Heavy infestations on roots or above-ground portions of the tree can stunt growth and even kill young trees.
Cultural Controls
- Lacewings, lady beetles, and syrphid fly larvae are predators, as well as the parasitic wasp Aphelinus mali.
- Predators will consume all but the waxy secretion left by the aphids.
- This aphid is considered a minor pest in the PNW.
- If colonies are found on trees, they can be physically removed.
- Many Geneva and Malling-Merton rootstocks are resistant.
- Management-