Japanese Maple Scale (Lopholeucaspis japonica (Cockerell)), Family Diaspididae
Plants Damaged: Japanese maple scale is showing up in more and more landscapes and nurseries lately. Look for this scale on Japanese maple, American red maple, dogwood, zelkova, lilac, yellowwood, pyracantha, privet, holly, euonymus, redbud, stewartia, cherry, magnolia, Itea, and styrax.
Damage Symptoms: This armored scale feeds directly on plant cells, not in the phloem tissue like soft scale insects. Heavy populations cause a slow decline of the tree. If high populations have resulted in dead branches on trees, prune these out before crawler hatch to reduce the number of scales potentially moving onto other branches and trees.
Life Cycle: The life cycle is poorly understood. The male and females overwinters as immatures and mature in early spring. There are two generations per year. The 2 generations overlap and crawlers are present from May through October.
Monitoring: Look for the white to gray, narrow oyster shell shaped female covers on twigs and main branches. Use a hand lens to look for the light purple crawlers. They should be out in late May or early June. Activity peaks in June to early July, and then we have a second crawler period in late July to mid September
Control: Applications of 1% horticultural oil and Distance should be made when crawlers are detected. This should have about 2 - 3 week residual activity. At that time monitor your plants again to see if crawlers are still active. The twice-stabbed lady bird beetle provides some biological control of this scale.
Information from "Scales Commonly Encountered in Maryland Landscapes and Nurseries" by Stanton Gill, Extension Specialist in IPM for Nurseries and Greenhouses,and Suzanne Klick and Shannon Wadkins, Technicians, Central Maryland Research and Education Center University of Maryland Cooperative Extension.
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