Pear slug
Caliroa cerasi
19 host plants
Last updated
You will find olive-green, slug-like larvae with glossy slime coating on the upper leaf surfaces of pear, cherry, hawthorn, and mountain ash trees. Feeding damage creates a skeletonized appearance as larvae consume tissue between veins. Mature larvae are orange-yellow. Multiple overlapping generations cause repeated defoliation from late April through summer. Young trees suffer the most impact.
Remove infested leaves and prune heavily damaged shoots to improve appearance. Hand-pick larvae clustering on lower canopy leaves. Spray strong water streams to dislodge small larvae. Encourage parasitic wasps and natural enemies. Time applications for May and July targeting young larvae before heavy feeding. Dormant cultivation may reduce pupae. Avoid pesticides that harm beneficial insects.
Quick Reference
Pear slug Emergence (est.) typically begins around 4323 GDD₃₂. As of June 3, 2026, Puget Sound stations range from 2435.5 to 2672.8 GDD₃₂, approximately 1650 units before the expected threshold.
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 | Pre-season | Emergence (est.) | 1,650 |
| Kent / Auburn | 2,665 | Pre-season | Emergence (est.) | 1,658 |
| Seattle / UW | 2,610 | Pre-season | Emergence (est.) | 1,713 |
| Olympia / Tumwater | 2,570 | Pre-season | Emergence (est.) | 1,754 |
| Tacoma / Puyallup | 2,535 | Pre-season | Emergence (est.) | 1,788 |
| Bellingham / Whatcom | 2,533 | Pre-season | Emergence (est.) | 1,790 |
| Sequim / Rain Shadow | 2,436 | Pre-season | Emergence (est.) | 1,888 |
Source: Pest GDD Catalog (UMD IPMnet), Added 2026-04-03 About GDD₃₂ →
Cultural Controls
- Natural enemies control pear slug populations fairly effectively.
- Specific biocontrol agents are not known, but this is rarely a pest in backyard gardens, so significant biocontrol likely occurs most years.
- Avoid use of broad-spectrum insecticides which can kill beneficial insects.
- Wash pear slugs from trees with a strong stream of water.
- Hand removal is effective on small trees.