Elm leafminer
Fenusa ulmi
8 host plants
Last updated
Elm leafminer larvae create winding, serpentine mines within American elm leaves starting in late spring through summer. You will see pale, snaking trails inside the leaf tissue with brown, dead tissue along the mines. Infested leaves become unsightly and may drop prematurely. Damage accumulates through the growing season. The pest is generally minor in home settings, causing appearance issues rather than serious tree decline.
This is primarily a cosmetic problem in landscape settings. Prune out heavily mined branches if appearance is important. No chemical treatment is justified given that trees tolerate leaf loss well. Encourage natural parasitoids that keep leafminer populations in check. Maintain tree vigor through proper watering to promote rapid recovery and regrowth of damaged foliage. Most elms in home gardens show only minor mine damage without any management intervention.
Quick Reference
Elm leafminer Adult emergence typically begins around 1116 GDD₃₂. As of May 13, 2026, all seven Puget Sound stations have passed this threshold (1906.2–2098.2 GDD₃₂), so Adult emergence 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 | Adult emergence | — | — |
| Kent / Auburn | 2,089 | Adult emergence | — | — |
| Seattle / UW | 2,063 | Adult emergence | — | — |
| Olympia / Tumwater | 2,025 | Adult emergence | — | — |
| Tacoma / Puyallup | 1,993 | Adult emergence | — | — |
| Bellingham / Whatcom | 1,972 | Adult emergence | — | — |
| Sequim / Rain Shadow | 1,906 | Adult emergence | — | — |
Source: Herms (OSU) phenological tables: 219 GDD₅₀ adult emergence, Secrest Arboretum OH 1997-2001 (Table 4); 228 GDD₅₀ Dow Gardens MI 1985-1989 (Table 3). UMD IPMnet Pest Predictive Calendar corroborates (Gill & Klick, base 50°F, Jan 1 biofix). Updated 2026-04-03. About GDD₃₂ →
Adult moths are about 0.12 inch in length. Wings are held roof-like over the body and are golden bronze with white bands. The larvae vary in appearance depending on their age, as they progress through five instars. Young larvae are legless and cream-colored. Older instars have legs and are cylindrical in shape, cream-colored and about 0.125 inch in length. Mature larvae are yellow and about 0.167 inch in length. The larvae feed within the leaf tissue creating dead discolored areas on leaves. If...
Cultural Controls
- Natural predators may help control populations.
- Pinch, or pick and destroy, infested leaves to kill larvae.