Boxwood leaf miners are serious pests. They prefer American boxwood but will attack English and Japanese boxwoods.
The larvae (small maggots) create yellow oval areas, similar to blisters, on infested leaves (Figure 1). When abundant, damage can cause premature leaf drop, twig dieback, and increased susceptibility to winterkill. Maggots are present in leaves from June through March, pupating in late spring.
Adults (small orange gnats) emerge, mate, and lay eggs for 10 to 14 days from late May to early June (about the time Weigela blooms). Females use sharp egg-laying organs to create tiny puncture wounds in leaves into which they insert their eggs. There is only one generation each year.
- Shear off and destroy infested leaves before early spring when adults emerge.
- Insecticidal control options include applying a 12-month tree and shrub systemic insecticide (containing imidacloprid or dinetofuran) after bloom to control the larval stages in leaves.
- A general tree and shrub insecticide can be applied to leave a residue on the foliage that kills females before they lay their leaves. This should be done now.
By Lee Townsend, Extension Entomologist