Spruce spider mite
Oligonychus ununguis
55 host plants
Last updated
You will see tiny yellow speckles and grayish spots on spruce needles, particularly on older foliage in the lower crown. Damage develops in spring and again in fall when temperatures cool. Needles may turn reddish-brown and eventually drop. Fine webbing traps debris between needles, making the tree appear dusty or discolored. Heavy infestations stunt branch growth and cause premature needle shedding.
Spider mites overwinter as eggs on needle surfaces; moderate winters support multiple generations yearly. Spray horticultural oil in late fall before bud break or use miticide at first sign of spring yellowing. Encourage natural predatory mites by avoiding broad-spectrum pesticides. Frequent irrigation reduces mite pressure.
Quick Reference
Spruce spider mite Egg hatch typically begins around 976 GDD₃₂. As of April 3, 2026, all seven Puget Sound stations have passed this threshold (1070–1180.6 GDD₃₂), so Egg hatch is likely underway across the lowlands.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | Egg hatch | — | — |
| Seattle / UW | 1,171 | Egg hatch | — | — |
| Kent / Auburn | 1,111 | Egg hatch | — | — |
| Olympia / Tumwater | 1,106 | Egg hatch | — | — |
| Bellingham / Whatcom | 1,101 | Egg hatch | — | — |
| Tacoma / Puyallup | 1,075 | Egg hatch | — | — |
| Sequim / Rain Shadow | 1,070 | Egg hatch | — | — |
Source: UMD IPMnet catalog. Rutgers: 7-121 GDD₅₀ activity window. Sources: Rutgers: plant-pest-advisory.rutgers.edu. About GDD₃₂ →
Cultural Controls
- Predaceous mites and insect predators such as ladybird beetles may naturally control spider mite levels.
- Avoid use of broad-spectrum insecticides that kill these predators.
- Wash spider mites from plants with a strong stream of water.
- Keep plants healthy to increase pest tolerance.
- Switch to slow-release or lower-nitrogen fertilizers.
- High levels of nitrogen in the leaves can increase spider mite reproduction rates.