Boxwood leafminer (Monarthropalpus flavus, family Cecidomyiidae) damage is already becoming apparent.
The boxwood leafminer is a European import first reported in the U.S. in the early 1900s. It’s not known exactly when it arrived or how it arrived to North America. Regardless, the non-native midge fly is now common on its namesake host throughout Ohio.
Yearly feeding of this insect can seriously disfigure the shrubs, as damaged leaves are shed mid-summer. The insect is actually a fly, but its larval form, which looks like a tiny yellow worm (maggot), damages the leaves as it feeds between the upper and lower layer of the leaf. The damage we see now began last summer, but the damage is seldom noticed until spring.
Boxwood leafminer damage may be mistaken for winter injury and vice versa. Both produce similar symptoms when viewed at a distance.
Chemical control with an insecticide spray is difficult because the application must be timed with the emergence of the adult flies. Applying an insecticide spray when the adult flies emerge can reduce populations.