Spruce spider mite

Egg hatch Active

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

Order
Acari
Type
mite
Host Plants
55
GDD₃₂ Egg hatch
976
Indicator: Serviceberry first bloom
Peak Activity
March-June: Spring activity, egg hatch and population buildup. July-August: S...
Damage Severity
growth-reducing
Now: Spring Population BuildupHigh Risk

Multiple overlapping generations develop rapidly through spring. Peak feeding causes visible stippling and bronzing. This is the primary damage window.

Next: Summer Dormancy

Spruce spider mite Egg hatch typically begins around 976 GDD₃₂. As of June 3, 2026, all seven Puget Sound stations have passed this threshold (2435.5–2672.8 GDD₃₂), so Egg hatch is likely underway across the lowlands.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Jun 3, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 2,673 Egg hatch — —
Kent / Auburn 2,665 Egg hatch — —
Seattle / UW 2,610 Egg hatch — —
Olympia / Tumwater 2,570 Egg hatch — —
Tacoma / Puyallup 2,535 Egg hatch — —
Bellingham / Whatcom 2,533 Egg hatch — —
Sequim / Rain Shadow 2,436 Egg hatch — —
Regional estimate

Source: UMD IPMnet catalog. Rutgers: 7-121 GDD50 activity window (base 50F, March 1 start). UMass: 150 GDD (Jan 1 biofix). Profile uses 179 GDD50 (UMD) as emergence threshold. About GDD₃₂ →

Monitoring & Action

How to Monitor

Tap suspect branches sharply over a white sheet of paper; look for tiny dark-colored specks that move. A 10x hand lens confirms identity. Monitor in spring (March-May) and fall (September-October) when mites are active. Check inner and lower branches first, where infestations typically begin. Do NOT rely on summer scouting: mites are dormant in summer heat.

When to Act

No formal threshold for landscape conifers. The presence of more than 10 mites per tap sample, or visible bronzing progressing outward from interior needles, justifies intervention. On high-value specimens (dwarf Alberta spruce, specimen blue spruce), treat at first detection of active mites and stippling.

What Damage Looks Like

Mites feed by piercing individual needle cells and extracting contents. Initial damage appears as tiny yellow or white stippling on needles. As feeding continues, needles become bronze, rusty brown, or grey-green. Fine silk webbing accumulates on needles and catches dust, further discoloring foliage. Heavily infested conifers develop a dull, off-color appearance that progresses from the interior outward and from lower branches upward. Severe infestations cause premature needle drop. Repeated heavy infestations can kill branches and, on small or stressed trees, entire plants. Damage is most visible in late spring and again in fall.

Cultural Controls

  • Maintain plant vigor through proper irrigation. Drought-stressed conifers suffer far more mite damage than well-watered trees.
  • Wash mites from foliage with a strong stream of water directed at inner and lower branches. Repeat weekly during active periods.
  • Avoid broad-spectrum insecticides (pyrethroids, carbaryl) that kill predatory mites and other natural enemies, often causing mite outbreaks to worsen.
  • Reduce nitrogen fertilization. High foliar nitrogen increases mite reproduction rates.
  • Prune out heavily damaged interior branches to improve air circulation and reduce mite habitat.

Host Plants (55)

Abies alba European Silver Fir, Common Silver Fir Abies amabilis Pacific Silver Fir Abies balsamea Balsam Fir Abies concolor White Fir, Colorado Fir Abies delavayi Delavay's Fir Abies grandis Grand Fir Abies koreana Korean Fir Abies lasiocarpa Subalpine Fir Rocky Mountain Fir, Alpine Fir Abies magnifica California Red Fir, Red Fir, Slivertip Fir Abies nordmanniana Nordmann Fir, Caucasian Fir Abies numidica Algerian Fir Abies pindrow West Himalayan Fir, Pindrow Fir Abies pinsapo Spanish Fir, Spanish Pin Fir Abies pinsapo subsp. marocana Moroccan Fir Abies procera Noble Fir Juniperus californica California Juniper, California White Cedar, Desert White Cedar Juniperus cedrus Canary Island Juniper Juniperus chinensis Chinese Juniper Juniperus communis Common Juniper Juniperus conferta Juniperus conferta Juniperus deppeana Alligator Juniper, Checkered-bark Juniper Juniperus formosana Formosan Juniper Juniperus grey Juniperus grey Juniperus horizontalis Creeping Juniper Juniperus monosperma Oneseed Juniper Juniperus occidentalis Western Juniper Juniperus osteosperma Utah Juniper Juniperus pingii Ping Juniper Juniperus procumbens Japanese Garden Juniper, Bonin Island Juniper, Ibuki Juniper Juniperus rigida Temple Juniper, Needle Juniper Juniperus rigida subsp. conferta Shore Juniper Juniperus sabina Savin Juniper Juniperus scopulorum Rocky Mountain Juniper Juniperus squamata Singleseed Juniper, Flaky Juniper, gao shan bai Juniperus virginiana Eastern Redcedar Pencil Cedar Picea abies Norway Spruce Picea abies var. pendula Weeping Norway Spruce, Pendulous Norway Spruce Picea asperata Dragon Spruce Picea breweriana Brewer Spruce, Brewer's Weeping Spruce Picea engelmannii Engelmann Spruce Picea gemmata Szechwan Spruce Picea glauca White Spruce, Canadian Spruce, Skunk Spruce Picea koyamae Koyama's Spruce, Yatsugatake-tohi [Japanese] Picea mariana Black Spruce, Bog Spruce, Swamp Spruce Picea omorika Serbian Spruce Picea orientalis Caucasian Spruce, Oriental Spruce Picea pungens Colorado Spruce Picea pungens var. glauca Colorado Blue Spruce Picea rubens Red Spruce Picea sitchensis Sitka Spruce Picea wilsonii Wilson's Spruce Pseudotsuga macrocarpa Bigcone Douglas-fir Pseudotsuga menziesii Douglas-fir Pseudotsuga menziesii var. glauca Rocky Mountain Douglas-fir Blue Douglas-fir Inland Douglas-fir Colorado Douglas-fir Pseudotsuga wilsoniana Taiwan Douglas-fir

Spruce spider mite is common on ornamental spruce, juniper, arborvitae, and Douglas-fir throughout Western Washington. The cool maritime climate extends the spring activity window (March through June), as sustained summer heat that triggers dormancy arrives later than in continental climates. Fall resurgence is also significant in the Puget Sound region, with activity from September through November. Dwarf Alberta spruce (Picea glauca 'Conica') is the most frequently damaged landscape host locally. Drought stress on conifers during the dry summer months (July-September) exacerbates fall mite damage.

— Chris Welch, ISA Certified Arborist

Sources & References

Primary: UMass Extension Landscape, Nursery & Urban Forestry Program - Insect & Mite Guide: Oligonychus ununguis

Data Maturity
Structured Multiple sources. Expert review underway.