BOXWOOD LEAFMINER adults should be emerging from leaves during 192-796 [366 peak] GDD base 50. Adults are small orange-yellow to red and are gnat-like. They commonly attack Buxus microphylla and B. sempervivens but cultivars such as 'Handworthiensis', 'Pyramidalis' and 'Varder Valley' are reported to be resistant. Females mate and die shortly after ovipositing eggs into boxwood leaves. Eggs hatch after three weeks and yellowish larvae feed inside leaves, causing a blister-like blotch to form on leaf undersides. Infested leaves may be slightly discolored. There is only one generation per year and larvae overwinter inside leaves and pupate at 48-585 [204 peak] GDD base 50
There is little information known regarding natural enemies of the boxwood leafminer. A cultural control method is to remove infested leaves prior to pupation. Chemical controls may target either larvae or adults. Time products targeting adults to coincide with emergence (approx. at weigela bloom). Available products include abamectin, bifenthrin or other pyrethroids, carbaryl, imidacloprid, dinotefuran and novaluron. Casey and I conducted a trial evaluating fall soil injections of dinotefuran and imidacloprid to infested boxwoods. Dinotefuran provided about 70% control of boxwood leafminers by two weeks whereas midacloprid took more than three months to obtain about 65% control. Imidacloprid persisted in boxwood longer than dinotefuran treatments but imidacloprid also caused increases in boxwood spider mite populations. Our project did not investigate how a spring application of dinotefuran will affect spider mites.
Boxwood leafminer larvae feeding. Photo by Nancy Gregory, UD Plant Diagnostic Lab.Information from Brian Kunkel, Extension IPM Specialist, UD.
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