Balsam woolly adelgid
Adelges piceae
15 host plants
Last updated
Inspect branches and main stems of silver fir and other true firs closely for small cottony white masses clustered on bark; these are colonies of adelgids covered in white waxy material. Heavy infestations can stunt branch growth or cause branch dieback. Swollen knots may form where adelgids feed on young growth.
Maintain tree vigor through adequate moisture and wind protection; healthy trees tolerate adelgid feeding better. Prune heavily infested twigs in winter when pests dormant. Horticultural oil applied in March coats overwintering stages and reduces spring populations. Apply insecticidal soap when crawlers are active in spring or early summer. This pest causes more damage in coastal areas.
Quick Reference
Balsam woolly adelgid Emergence (est.) typically begins around 1143 GDD₃₂. As of April 21, 2026, all seven Puget Sound stations have passed this threshold (1393.7–1554.7 GDD₃₂), so Emergence (est.) is likely underway across the lowlands.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 21, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,555 | Emergence (est.) | — | — |
| Seattle / UW | 1,516 | Emergence (est.) | — | — |
| Kent / Auburn | 1,497 | Emergence (est.) | — | — |
| Olympia / Tumwater | 1,467 | Emergence (est.) | — | — |
| Bellingham / Whatcom | 1,440 | Emergence (est.) | — | — |
| Tacoma / Puyallup | 1,434 | Emergence (est.) | — | — |
| Sequim / Rain Shadow | 1,394 | Emergence (est.) | — | — |
Source: UMD IPMnet, Pest GDD Catalog, Added 2026-04-03 About GDD₃₂ →
Cultural Controls
- Hand-wipe to remove minor infestations when possible.
- Hose infested trees with strong stream of water to wash off these insects.
- Ladybird beetles and syrphid fly larvae help control adelgid populations.
- Avoid use of broad-spectrum insecticides which will kill these important predators.