Boxwood leafminers feed and develop within plant leaves. Heavily mined leaves usually turn yellow and may drop prematurely, but the leaf drop usually doesn’t have a significant impact on otherwise healthy plants.
Natural enemies can be effective in managing infestations. If this insect has been a problem, application of insecticides such as carbaryl (Sevin), cyfluthrin (Bayer Multi-Insect Killer Concentrate, or permethrin (Bonide Borer Miner Killer, and others) about the time of Weigela bloom should provide preventive control. Products containing acephate (Orthene and others) can give some control if mines are developing.
Boxwood psyllids are flat, green, sap-feeding insects that cause spring terminal growth to cup (Figure 3). The damage is especially noticeable on American boxwood. While the small nymphs (Figure 4) blend well with the foliage, the white waxy strands that they produce are very easy to see (Figure 5). These insects affect the appearance of the plant but are not a threat to plant health or vigor. Fortunately, distorted leaves usually fall off in about a year and the plants can recover. More information is available in Boxwood Psyllids (EntFact-454)
By Lee Townsend, Extension Entomologist