European elm scale
Gossyparia spuria
8 host plants
Last updated
European elm scale appears as small, flat, reddish-brown bumps on American elm bark, particularly on trunks and older branches. You will see oozing sap and sooty mold accumulation beneath scale infestations. Heavy infestations can girdle branches and cause significant dieback. Scales overwinter on bark and remain relatively inconspicuous until populations build.
Apply horticultural oil in late dormancy before buds open. Encourage natural parasitoids and predatory beetles by avoiding insecticides. Prune heavily infested branches. Maintain tree vigor through proper watering and wound care.
Quick Reference
European elm scale Egg hatch/crawler typically begins around 2946 GDD₃₂. As of May 13, 2026, Puget Sound stations range from 1906.2 to 2098.2 GDD₃₂, approximately 848 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 13, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,098 | Pre-season | Egg hatch/crawler | 848 |
| Kent / Auburn | 2,089 | Pre-season | Egg hatch/crawler | 857 |
| Seattle / UW | 2,063 | Pre-season | Egg hatch/crawler | 883 |
| Olympia / Tumwater | 2,025 | Pre-season | Egg hatch/crawler | 921 |
| Tacoma / Puyallup | 1,993 | Pre-season | Egg hatch/crawler | 953 |
| Bellingham / Whatcom | 1,972 | Pre-season | Egg hatch/crawler | 974 |
| Sequim / Rain Shadow | 1,906 | Pre-season | Egg hatch/crawler | 1,040 |
Source: UMD IPMnet catalog. Sources: UMD: extension.umd.edu. About GDD₃₂ →
Cultural Controls
- A strong stream of water will wash off some scales.
- This is most effective in spring, before leaves emerge.
- Provide proper culture to maintain plant health.
- Healthy trees are more able to tolerate scale infestations.
- Asiatic elms such as Siberian elm (Ulmus pumila) and Chinese elm (U.
- parvifolia) are apparently not infested.