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I am sending you information that you will find helpful in controlling the boxwood leaf miners and psyllids. If you need further information let me know.
Control of the boxwood leafminer should begin with the selection of the more resistant varieties mentioned above. Pruning the foliage before adult emergence or after egglaying ends will help to reduce the overall population of egglaying adults. Chemical control is difficult because the application must be timed with the emergence of the adult flies. An application of an insecticide spray when the adult flies emerge – this corresponds to when weigela is in bloom – can reduce populations. Insecticide sprays containing bifenthrin (Talstar), carbaryl (Sevin), cyfluthrin (Tempo or Bayer Advanced Garden Insect Control) or malathion are among the recommended materials that can be applied to control the adult flies. Imidacloprid, a systemic insecticide (Merit or Bayer Tree and Shrub Insect Control), will control the larvae inside the leaves and does not require precise timing. This product should be applied in mid- to late April.

Boxwood psyllid

The boxwood psyllid, Cacopsylla busi, is a less serious pest that occurs wherever boxwoods are grown. It causes cupping of leaves and may affect twig growth, but the damage caused is purely aesthetic and not as destructive as other boxwood pests. The boxwood psyllid is a common pest of all boxwoods, but the American boxwood (Buxus sempervirens) is most susceptible.

This insect overwinters as a tiny, orange egg deposited in the bud scales. The eggs hatch in the spring when the buds of the host plant open. The nymphs immediately begin to feed and develop white, waxy strands over their bodies. Winged adults appear by early June. After mating, the female deposits her eggs between the bud scales of the host plant. There is one generation each year.           This information came from Michigan State University.  Thank you for using Ask an Expert.