Boxwood psyllid
Psylla buxi
5 host plants
Last updated
On boxwood foliage you will see cupped or sagging leaves beginning in late spring, with tiny whitish insects visible on undersides and small white flocculent material (waxy coating) covering them. Heavy infestations cause stunted or distorted new growth and plant decline. Look for this pest on boxwood species during May and June.
Prune out cupped or severely distorted new growth in spring to remove overwintering nymphs before maturity. Apply horticultural oil in late March or early April, coating thoroughly to target dormant nymphs. If new infestations appear in late May, apply insecticidal soap to new growth when nymphs active. Some cultivars show natural resistance.
Quick Reference
Boxwood psyllid Egg hatch typically begins around 994 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: Herms (OSU) phenological tables: 179 GDD₅₀ egg hatch, Secrest Arboretum OH 1997-2001 (Table 4). Profile value 184 near-match. UMD IPMnet catalog corroborates. Updated 2026-04-03. About GDD₃₂ →
Cultural Controls
- Do not force plants into accelerated growth, as psyllids prefer new, succulent growth for feeding.
- Clip distorted terminals to improve appearance of plants.
- Otherwise, minimize shearing of plants, since it stimulates new growth preferred by psyllids.
- Conserve naturally-occurring predators such as ladybird beetles, lacewings, and parasitic wasps.
- Avoid use of broad-spectrum insecticides which kill these beneficial insects.