Twospotted spider mite
Tetranychus urticae
1 host plant
Last updated
Twospotted spider mites are tiny, round, and ranging from greenish-yellow to red depending on season and host. Heavy webbing on plant foliage appears grayish or tan, trapping dust and giving plants a dirty appearance. Infested leaves become pale yellow with brown feeding spots. This mite attacks a wide range of plants and favors warm, dry conditions.
Increase humidity by frequent foliar misting or regular overhead irrigation to reduce mite populations. Strong water spray dislodges mites from foliage. Release predatory mites (Phytoseiulus species) for biological control on high-value plants. Apply horticultural oil or sulfur before mite populations explode. Miticides are a last resort; avoid use if natural predators are present.
Quick Reference
Twospotted spider mite Egg hatch typically begins around 2375 GDD₃₂. As of May 9, 2026, Puget Sound stations range from 1800.9 to 1983.6 GDD₃₂, approximately 391 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 9, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,984 | Pre-season | Egg hatch | 391 |
| Kent / Auburn | 1,972 | Pre-season | Egg hatch | 403 |
| Seattle / UW | 1,954 | Pre-season | Egg hatch | 421 |
| Olympia / Tumwater | 1,913 | Pre-season | Egg hatch | 462 |
| Tacoma / Puyallup | 1,881 | Pre-season | Egg hatch | 494 |
| Bellingham / Whatcom | 1,863 | Pre-season | Egg hatch | 512 |
| Sequim / Rain Shadow | 1,801 | Pre-season | Egg hatch | 574 |
Source: UMD IPMnet Pest Predictive Calendar (Gill & Klick, UMD Extension; base 50°F, Jan 1 biofix, mid-Atlantic Zone 7a-7b). Population increase. extension.umd.edu About GDD₃₂ →
Adults are about 2-3 mm long, have eight legs, and are light tan or greenish with a dark spot on each side of the back. Mite feeding reduces plant vigor and may cause leaves to curl, turn brown, and drop prematurely reducing yield. Spider mite feeding is accompanied by webbing on the undersides of the leaves.
Cultural Controls
- Rain and cool temperatures tend to suppress mite populations.
- Considerable natural control is provided by lady beetles and minute pirate bugs (Orius spp.).
- Predatory mites such as Typhlodromus spp. or Neoseiulus fallacis (syn.
- Amblyseius fallacis) are also effective at managing populations of spider mites and may be purchased and released.
- Use according to supplier's directions.
- Excessive nitrogen fertilization may cause population buildup.
Host Plants (1)
Sources & References
Primary: PNW Insect Management Handbook