As our arborists and techs conduct their Plant Health Care treatments, they are noticing quite a few leaf blisters in boxwoods. These blisters contain the young larvae of the Boxwood Leafminer which continues to be the primary pest in boxwood. Over several years, a lightly infested plant can become discolored, brown and even defoliated, but when the population of the leafminer is severe, they will kill the boxwoods.
Their life cycle begins in spring. Leaves that contain the larvae blisters hold young larvae that grow and feed just under the epidermal cell of the leaf. In April or early May the pupae emerge from the leaf as adults, and to the naked eye, the adults appear to be an orange mosquito. They are weak flyers and generally hover within inches of the boxwood after hatching because a slight gust of wind will blow them away. Leafminers generally pupate over a three week period. The adults mate and the female lays eggs in the tender new growth of the boxwood. Sometime in early summer the eggs hatch, and the larvae begin their cycle of growth concluding the following spring.
These pests are controllable, and options are simplified because only one generation of leafminers are produced each year. The main objective is to kill the adults. Therefore, when treatments are applied properly and thoroughly to all the boxwoods in a given area, the leafminers can be managed.
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