Pear psylla
Cacopsylla pyricola
3 host plants
Last updated
You will see tiny yellowish insects with piercing-sucking mouthparts on pear foliage from early spring through fall. Heavy infestations produce abundant honeydew that causes fruit russet and leaf sooty mold. Nymphs cluster on buds and leaves. Damage includes stunting, defoliation, and unmarketable fruit. Pear psylla overwinters as adults and is the most challenging pest for Washington pear growers.
Monitor egg hatch in spring as buds swell. Time dormant oils or insecticidal soaps for early season when crawlers are vulnerable. Maintain vigilant scouting throughout the growing season to prevent population buildup. Predatory insects including minute pirate bugs and parasitic wasps attack psylla. Avoid broad-spectrum insecticides that kill beneficial insects essential for pear psylla control.
Quick Reference
Monitoring & Action
Limb-tap sampling: hold a white sheet or clipboard under a branch and sharply strike the branch. Count dislodged adults. Sample 5-10 branches per block. Also check new shoot growth for nymphs (visible as yellow flattened insects surrounded by honeydew). Sticky yellow traps can track adult flight timing but are less useful for population assessment.
Commercial orchards: 0.2 to 0.5 adults per limb-tap through the dormant and green-tip period; higher thresholds (2-5 per tap) may be tolerated once natural enemies are established. Home orchards: treat when honeydew is dripping onto fruit or when leaves show significant blackening/burn.
Nymphs feed on leaves with piercing-sucking mouthparts, preferring succulent new growth in the upper canopy. Feeding produces copious honeydew (a sweet, sticky excretion) that drips onto leaves and fruit below. Honeydew on fruit causes cosmetic russeting that downgrades packout quality. On leaves, honeydew promotes sooty mold growth, which blackens foliage and reduces photosynthesis. Heavy infestations cause leaf scorch (psylla burn), with blackened or burned-looking leaves. Honeydew also attracts ants and yellowjackets. Pear psylla can vector the phytoplasma that causes pear decline, a serious vascular disease.
Cultural Controls
- Conserve natural enemies in the orchard WSU HortSense
- Avoid excess nitrogen fertilization PNW Insect Management Handbook
- Remove root suckers and watersprouts WSU HortSense
- Open canopy through pruning PNW Insect Management Handbook
Host Plants (3)
Pear psylla is primarily a concern for home pear orchards and ornamental pear plantings in the Puget Sound lowlands. The mild maritime winters allow some adults to remain active later into fall and return earlier in spring compared to colder inland regions. Ornamental Callery pears (P. calleryana) along streets and in landscapes can harbor populations near home orchards. In the Kent area, overwintered adults typically return to pear trees by late February. The wet spring conditions promote honeydew-related sooty mold. Conservation of natural enemies is especially effective here since most home orchardists don't spray, allowing predator populations to build.
— Chris Welch, ISA Certified Arborist
Sources & References
Primary: PNW Insect Management Handbook
- WSU Tree Fruit Pear Psylla Phenology Model
- UC Davis IPM Pear Psylla
- Horton et al. 1992 (Yakima WA + Medford OR field studies, base 41F)
- 2026 Pest Management Guide for Tree Fruits
- 2026 Crop Protection Guide for Tree Fruits in Washington
- OSU organic orchards stakeholder assessment — pear psylla priority