Amanda Taylor, Area Specialized Agent
– Nursery and Greenhouse alerted us that Boxwood leafminer
adults are active in the Lenoir area. Adult leafminers are delicate orange flies that hover in large numbers around boxwood plants. They are only active for a couple weeks each year. They will continue to emerge over the next couple of weeks and then lay eggs inside of boxwood leaves. The larvae develop within the leaves creating blister mines and discoloring the leaves.
Boxwood leafminer adult. Photo: SD Frank
Insecticide applications targeting the adults now can reduce the number of adults that land on the bushes and lay eggs. This can reduce the number of mines in the coming year. Contact insecticides containing abamectin, bifenthrin, permethrin, pyripoxyfen, or spinosad will kill adults. Nursery growers have the option of using Discus, a combination of a contact insecticide (which will kill adults) and a systemic insecticide (which will kill larvae). Other insecticides are in the Southeastern US Pest Control Guide for Nursery Crops and Landscape Plantings.
Boxwood leafminer larvae in a boxwood leaf. Photo: SD Frank
If you miss the adults, the larvae that are inside the leaf can be killed with a systemic neonicotinoid insecticide such as imidacloprid or dinotefuran. Caution should be exercised with any insecticide applications since boxwoods are also flowering now and their flowers are very attractive to bees, flies, and other pollinators.
Boxwood flowers and leaf blisters occur simultaneously in spring. Photo: SD Frank