Boxwoods in the landscape not looking so good? Are you seeing a lot of yellow-brown spots on leaves?
Look at the undersides of leaves for empty pupal cases partially sticking out of the epidermis, this is a sure sign the boxwood leafminer adults have emerged!
ADULTS ARE FLYING and MATING and can be found on the newest leaves where the black locust (Robinia pseudoacacia) are blooming stage (e.g. Toronto). The tiny orange midge adults resemble tiny mosquitoes and emerge out of last year’s leaves. Adult midges lay their eggs into newly emerged leaves and those eggs will hatch into the next generation of leaf miners. Treating new foliage with insecticides at the beginning (or just prior to) adult emergence can help reduce successful egg hatch and leafminer establishment in the nursery. Avid (abamectin) miticide/insecticide is now registered for boxwood leafminer in nursery production and is very effective.
This pest is more common in the landscape. Insecticidal soap can be used to suppress adults in the landscape when used as an early morning application (cooler temperatures, less midge activity). Landscapers can also prune out infested new foliage in July/August. The infested clippings will desiccate, making it impossible for the freeloading leafminer larvae to complete their life cycle into next spring.