Hemlock scale
Hemiberlesia ithacae
22 host plants
Last updated
Hemlock scale insects appear as small, flat, brownish oval bumps covering the needles and twigs of spruce and other conifers. The scales settle in dense populations, giving infested areas a bumpy, crusty appearance. Heavy infestations cause needle yellowing, branch dieback, and reduced growth vigor, particularly in young landscape plantings. You identify them by their immobile appearance and textured surface.
Apply dormant oil in late winter or early spring to smother overwintering scale. For growing-season populations, horticultural oil targets the crawler stage in early summer. Maintain tree vigor with appropriate watering and avoid stress. Prune out severely infested branches. For high-value trees, a second oil application in mid-summer targets new generations; timing is critical.
Quick Reference
Hemlock scale Emergence (est.) typically begins around 1044 GDD₃₂. As of May 14, 2026, all seven Puget Sound stations have passed this threshold (1926.1–2121.1 GDD₃₂), so Emergence (est.) is likely underway across the lowlands.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 14, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,121 | Emergence (est.) | — | — |
| Kent / Auburn | 2,113 | Emergence (est.) | — | — |
| Seattle / UW | 2,085 | Emergence (est.) | — | — |
| Olympia / Tumwater | 2,047 | Emergence (est.) | — | — |
| Tacoma / Puyallup | 2,016 | Emergence (est.) | — | — |
| Bellingham / Whatcom | 1,994 | Emergence (est.) | — | — |
| Sequim / Rain Shadow | 1,926 | Emergence (est.) | — | — |
Source: Pest GDD Catalog (UMD IPMnet), Added 2026-04-03 About GDD₃₂ →
Cultural Controls
- Provide proper culture.
- Healthy plants are less likely to be infested and more tolerant of damage.
- Prune and destroy branches with heavy, isolated infestations (when practical).