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 April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂, approximately 40 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | Pre-season | Adult emergence | 40 |
| Seattle / UW | 1,171 | Pre-season | Adult emergence | 50 |
| Kent / Auburn | 1,111 | Pre-season | Adult emergence | 110 |
| Olympia / Tumwater | 1,106 | Pre-season | Adult emergence | 115 |
| Bellingham / Whatcom | 1,101 | Pre-season | Adult emergence | 120 |
| Tacoma / Puyallup | 1,075 | Pre-season | Adult emergence | 146 |
| Sequim / Rain Shadow | 1,070 | Pre-season | Adult emergence | 151 |
Source: UMD IPMnet catalog. Sources: UMD: extension.umd.edu. About GDD₃₂ →
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.