Boxwood leafminer
Monarthropalpus flavus
5 host plants
Last updated
Inspect boxwood leaves for blistered puffy appearance on undersides with orange or reddish tint; upper surface shows pale yellow or light green speckles where tiny larvae tunnel between layers. Heavily mined leaves turn brown and drop prematurely by late summer. Look for this damage on common boxwood throughout growing season.
Prune out and destroy heavily mined leaf clusters to remove developing larvae, particularly effective in spring when blisters first appear. Apply horticultural oil in late March to smother overwintering pupae before adults emerge. If mines appear later, remove and destroy infested leaves rather than spraying; boxwoods tolerate defoliation well. Repeat infestations may warrant resistant species.
Quick Reference
Boxwood leafminer Adult emergence typically begins around 1221 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: UMD IPMnet catalog. Sources: UMD: extension.umd.edu. Wisconsin Extension: Wisconsin Extension (landscape pest table). 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
- Plant varieties of English boxwood (Buxus sempervirens) such as 'Suffruticosa', 'Pendula', and 'Argenteo-varigata', which are reported to be seldom damaged.
- Pinch to kill maggots in infested leaves when practical.
- Pick and destroy infested leaves when practical.
- Provide proper culture to maintain plant health.
- Healthy plants are more tolerant of insect damage.
- Natural predators may help control populations.