Spruce budworm
Choristoneura fumiferana
30 host plants
Last updated
True fir forests east of the Cascade crest suffer most, though you may encounter this pest on landscape spruce and fir. Larvae feed on buds and growing tips, webbing the branch terminals together. Look for reddish-brown foliage by mid-summer on susceptible hosts like subalpine fir and grand fir. Damage accumulates over three to five years of consecutive defoliation, causing branch loss and crown thinning.
Most forest and shade-tree populations are naturally suppressed by parasitoid wasps and flies. For ornamentals, prune infested twigs and burn pruning material to eliminate pupae. Monitor trees after pruning to ensure recovery. Do not apply broad-spectrum pesticides, as these kill natural enemies.
Quick Reference
Spruce budworm Emergence (est.) typically begins around 1160 GDD₃₂. As of May 13, 2026, all seven Puget Sound stations have passed this threshold (1906.2–2098.2 GDD₃₂), so Emergence (est.) is likely underway across the lowlands.
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 | Emergence (est.) | — | — |
| Kent / Auburn | 2,089 | Emergence (est.) | — | — |
| Seattle / UW | 2,063 | Emergence (est.) | — | — |
| Olympia / Tumwater | 2,025 | Emergence (est.) | — | — |
| Tacoma / Puyallup | 1,993 | Emergence (est.) | — | — |
| Bellingham / Whatcom | 1,972 | Emergence (est.) | — | — |
| Sequim / Rain Shadow | 1,906 | Emergence (est.) | — | — |
Source: MSU Extension conifer insect table: 200 GDD₅₀ first larval activity (Jan 1 biofix, MSU field observations). Not in Herms phenological tables (forest pest, not landscape). Species-specific to C. fumiferana. Updated 2026-04-03. About GDD₃₂ →
Cultural Controls
- Hand-pick and destroy on small trees (where possible).
- Avoid use of broad-spectrum insecticides which may kill natural predators and parasites including parasitic wasps.