Boxwood leafminer is a very common pest of boxwood, particularly American boxwood and littleleaf boxwood. The Sheridan series of boxwood such as ‘Green Mountain,’ ‘Green Pillow,’ and ‘Green Velvet’ are also sensitive. English boxwood is resistant.
These insects overwinter as partially grown larvae in boxwood leaves. In early spring, they complete development and emerge as small, gnat-like flies. Adults mate and lay eggs in developing boxwood leaf tissue in late April and May. The eggs hatch within three weeks and the larvae feed between leaf surfaces.
Signs of a boxwood leafminer infestation include blisters on the foliage that turn yellow with time. Larvae and pupae are visible between the leaf surfaces when leaves are dissected. Treatment option are available to help manage control an infestation.