Azalea Lace Bug
Stephanitis pyrioides
113 host plants
Last updated
Beginning in May, examine rhododendron foliage for pale speckled upper surfaces paired with brown varnished undersides concentrated with cast skins and frass. Tiny brown and tan adults resemble delicate lace patterns underneath leaves. Infested leaves eventually yellow or brown, creating aesthetic damage.
Forceful water spray to leaf undersides in early June disrupts nymphs. Apply horticultural oil or insecticidal soap every 10 days if lace bugs persist, timing sprays when daytime temperatures stay below 85F. Encourage natural parasitoid wasps and predatory mites by limiting pesticide use. Tolerating minor stippling maintains beneficial insects for long-term suppression.
Quick Reference
Azalea Lace Bug Egg hatch 1st gen typically begins around 1099 GDD₃₂. As of May 13, 2026, all seven Puget Sound stations have passed this threshold (1906.2–2098.2 GDD₃₂), so Egg hatch 1st gen 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 | Egg hatch 1st gen | — | — |
| Kent / Auburn | 2,089 | Egg hatch 1st gen | — | — |
| Seattle / UW | 2,063 | Egg hatch 1st gen | — | — |
| Olympia / Tumwater | 2,025 | Egg hatch 1st gen | — | — |
| Tacoma / Puyallup | 1,993 | Egg hatch 1st gen | — | — |
| Bellingham / Whatcom | 1,972 | Egg hatch 1st gen | — | — |
| Sequim / Rain Shadow | 1,906 | Egg hatch 1st gen | — | — |
Source: UMD Extension IPMnet Pest Predictive Calendar (Gill & Klick). 214 GDD₅₀, base 50°F, Jan 1 biofix. Rosetta (OSU NWREC) reports 213 GDD base 50.4°F (10.2°C); treat as equivalent. Mid-Atlantic derived. Note: base 50°F models are poor predictors of calendar date in maritime PNW because winter heat between 32-50°F is invisible to them. source: UMD Extension IPMnet; Rosetta, OSU NWREC About GDD₃₂ →
Monitoring & Action
Inspect undersides of leaves beginning at Deutzia first bloom (typically mid-April in the Puget Sound lowlands). Look for pale spiny nymphs aggregated near the midrib and black fecal spots. Upper-surface stippling appears 2 to 4 weeks after nymph emergence. A hand lens helps detect early instars. Focus on sun-exposed plants first. source: WSU HortSense; UMass Extension
No formally published quantitative threshold for ornamental plantings. Treat when early-instar nymphs are visible on multiple shoots. First-generation intervention (April) is significantly more effective than reactive treatment after adults disperse. source: HortGuide regional interpretation (based on WSU HortSense, NC State Extension, UMass Extension)
Piercing-sucking feeding removes cell contents from leaf mesophyll, producing a stippled or bleached pattern on the upper leaf surface. Affected leaves appear silvery-white to bronze. The underside of infested leaves shows dense black to brown fecal deposits ('tar spots') and cast nymphal skins. Damaged leaves do not recover their green color. Severe multi-year infestations cause chronic decline, reduced flowering, and in extreme cases plant mortality on susceptible hosts. source: WSU HortSense; Rosetta, OSU NWREC
Cultural Controls
- Site rhododendrons and azaleas in partial shade. The mechanism is biocontrol, not plant physiology: shaded, species-diverse landscapes support higher natural-enemy populations that suppress lace bug populations. UC IPM
- Avoid drought stress; water-stressed plants sustain more severe damage and recover more slowly. WSU HortSense
- Direct a strong stream of water at leaf undersides to dislodge nymphs; wingless nymphs cannot return to the plant. WSU HortSense
- Prune and dispose of heavily infested shoots in fall to reduce overwintering egg load. NC State Extension
- For chronic problems, consider replanting with resistant deciduous azalea species (R. atlanticum, R. arborescens, R. canescens, R. periclymenoides, R. prunifolium) or non-host alternatives (Camellia, Osmanthus, Daphne, Mahonia). UMass Extension; OSU SolvePest
- Avoid broad-spectrum insecticides that disrupt natural enemies, which can trigger secondary pest outbreaks (spider mites). UC IPM
Host Plants (113)
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— Chris Welch, ISA Certified Arborist
Sources & References
Primary: WSU HortSense
- Garrison, R.R. & Tobin, P.C. (2022). Development of Azalea Lace Bug, Stephanitis pyrioides, on Susceptible and Resistant Rhododendron species in Western Washington. J. Economic Entomology 115(1): 233–239. PubMed 34984439. — PNW generation count, degree-day model (171 GDD base 50.4°F for 50% nymph emergence), resistant cultivars
- Rosetta, R. Dealing with the Onslaught: IPM of Azalea Lace Bug. OSU NWREC. — Detection dates, novel host trials, base temperatures, GDD thresholds
- LaBonte, J. & Valente, R. Novel host poster. Oregon Dept. Agriculture. — Cage trial data for PNW native hosts
- Eigenbrode, S.D., Bosque-Pérez, N.A. et al. (2020). Attracting Chrysopidae with plant volatiles for lace bug control. J. Insect Science. PMC 7459699. — Quantitative biocontrol study
- Shrewsbury, P.M. & Smith-Fiola, D.C. (2000). Evaluation of green lacewings for suppressing azalea lace bug populations in nurseries. — 79-88% ALB reduction data
- PNW Insect Management Handbook — Azalea/Rhododendron lace bug.
- UMD Extension IPMnet Pest Predictive Calendar (Gill & Klick) — GDD threshold data.
- UMass Extension: Stephanitis pyrioides.