Euonymus scale
Unaspis euonymi
7 host plants
Last updated
Euonymus scale appears as tiny, flat bumps on the undersides of euonymus leaves and stems, clustering heavily to create a whitish-gray crust. You will see yellow, dying foliage as scales suck sap; affected branches may eventually die. Both male and female scales are present; females are larger and brown, males are white and narrow. Heavy infestations cause branch dieback and severe plant decline.
Spray horticultural oil during dormancy to smother overwintering females and reduce spring populations significantly. Encourage natural enemies, particularly parasitoid wasps and lady beetles, by avoiding broad-spectrum insecticides. In summer, target crawler emergence with insecticidal soap applied to leaf undersides when you see first movement. Prune out heavily infested branches. Improve plant vigor through proper watering and pruning; stressed plants are more susceptible to severe damage.
Quick Reference
Euonymus scale Egg hatch/crawler 2nd gen typically begins around 6390 GDD₃₂. As of May 13, 2026, Puget Sound stations range from 1906.2 to 2098.2 GDD₃₂, approximately 4292 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 2nd gen | 4,292 |
| Kent / Auburn | 2,089 | Pre-season | Egg hatch/crawler 2nd gen | 4,301 |
| Seattle / UW | 2,063 | Pre-season | Egg hatch/crawler 2nd gen | 4,327 |
| Olympia / Tumwater | 2,025 | Pre-season | Egg hatch/crawler 2nd gen | 4,365 |
| Tacoma / Puyallup | 1,993 | Pre-season | Egg hatch/crawler 2nd gen | 4,397 |
| Bellingham / Whatcom | 1,972 | Pre-season | Egg hatch/crawler 2nd gen | 4,418 |
| Sequim / Rain Shadow | 1,906 | Pre-season | Egg hatch/crawler 2nd gen | 4,484 |
Source: Herms (OSU) phenological tables: 575 GDD₅₀ egg hatch 1st generation, Dow Gardens MI 1985-1989 (Table 3); 406 GDD₅₀ Secrest Arboretum OH 1997-2001 (Table 4). MSU Extension and UMD IPMnet (522 GDD₅₀) corroborate mid-range. Profile range 400-575 brackets both Herms sites. Updated 2026-04-03. Rutgers: plant-pest-advisory.rutgers.edu (35-120 GDD₅₀ overwintered adults; 533-820 GDD₅₀ crawler emergence). Wisconsin Extension: Wisconsin Extension (landscape pest table). About GDD₃₂ →
Monitoring & Action
Visual inspection for white male scales on leaves. Double-sided sticky tape on stems for crawler detection.
Feeds on cell contents. Heavy infestations cause leaf yellowing, branch dieback, and plant decline. Male scales visible as white specks on leaves; female scales encrust stems.
Cultural Controls
- Plant resistant species. Euonymus alata (especially 'Compacta') and E. fortunei 'Acutus' are seldom infested. Several other species will tolerate scale feeding.
- Avoid Euonymus japonicus (evergreen euonymus), as it is extremely susceptible to scale infestations.
- Prune and destroy twigs with isolated heavy infestations.
- Hand-wipe to help control small infestations, when practical.
- Natural predators may help control infestations, but may not prevent damage.