Holly leafminer
Phytomyza ilicis
17 host plants
Last updated
This profile contains verified pest data from extension databases. Regional field notes and expert review are in progress.
Holly leafminer larvae create pale, serpentine tunnels within holly leaf tissue, leaving mines that follow a random, winding pattern across the leaf surface. The damage first appears in summer and becomes increasingly visible as mines enlarge through fall. You see the pale, papery trails within otherwise green leaves on Ilex species. Heavy mining can cause some leaf yellowing and drop, though leaves tolerate light mining.
Remove and destroy heavily mined leaves to reduce overwintering populations. For valuable ornamentals, apply horticultural oil in late winter to target pupae. Once mining is visible, spinosad or neem oil applied to leaf undersides targets young larvae. Apply every 7 to 10 days during mining season. Maintain plant vigor and adequate moisture.
Quick Reference
Holly leafminer Adult emergence typically begins around 1625 GDD₃₂. As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂, approximately 32 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 23, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,593 | Pre-season | Adult emergence | 32 |
| Seattle / UW | 1,554 | Pre-season | Adult emergence | 71 |
| Kent / Auburn | 1,537 | Pre-season | Adult emergence | 88 |
| Olympia / Tumwater | 1,505 | Pre-season | Adult emergence | 121 |
| Bellingham / Whatcom | 1,483 | Pre-season | Adult emergence | 142 |
| Tacoma / Puyallup | 1,472 | Pre-season | Adult emergence | 153 |
| Sequim / Rain Shadow | 1,434 | Pre-season | Adult emergence | 191 |
Source: Herms (OSU) phenological tables: 375 GDD₅₀ adult emergence, Secrest Arboretum OH 1997-2001 (Table 4). Exact match. UMD IPMnet catalog corroborates. Updated 2026-04-03. About GDD₃₂ →
Cultural Controls
- Hand-pick and destroy infested leaves in the fall.
- Pinch leaves to kill leafminers inside mines.
- Natural predators may help control populations.
- Encourage predators such as green lacewings and spiders.