Japanese maple scale (JMS), Lopholeucaspis japonica (Cockerell), is a non-native pest from Asia and was first detected in Connecticut in 1914. Since its introduction it has been confirmed from several additional eastern states. JMS can infest a wide range of woody ornamental plants commonly found in nurseries and landscapes. This insect pest is quite small and blends in well with host bark, allowing it to avoid detection until population levels are high. Feeding by the JMS causes reduced plant growth and vigor. Foliage may drop prematurely, giving plants a thin appearance and twig dieback may also occur.
Important landscape hosts include: apple, ash, camellia, cherry, cotoneaster, crabapple, dogwood, elm, euonymus, holly, honeylocust, hornbeam, Itea, lilac, linden, magnolia, maple, pear, privet, pyracantha, redbud, serviceberry, stewartia, styrax, yellowwood, and zelkova.
Symptoms & Life Cycle
JMS have an oystershell-shaped body covered in a white, waxy protective coating. Beneath this outer shell, the adult and nymph scales are lavender in color. Female scales are 1-2 mm long while males are slightly smaller. JMS are most commonly found on bark, though they can also occur on foliage. There is limited understanding of the life cycle of this pest, but in the colder climates of New England, JMS is likely to have only one generation and is thought to overwinter as fertilized adult females. In the spring, females lay approximately 25 eggs within their protective coverings. Eggs develop in late-spring, hatch, and crawlers (immature nymphs) emerge in mid-May. The timing of the initial crawler hatch seems to coincide with bloom of Syringa reticulata 'Ivory Silk' and Hydrangea quercifolia, so these events can be used as phenological indicators. The period of egg hatch and crawler activity lasts for a long period of time (about 10 weeks in the mid-Atlantic region). Two generations of egg laying occurs in southeastern and mid-Atlantic states, but in New England it's possible there is only one generation per growing season.
On shrubs, scouting for this pest should initially focus on the first eight inches above the soil line. For trees, meanwhile, scouting should take place on the trunks and scaffold branches, particularly at the branch collar. It is most effective to scout for JMS in the dormant season when it is easier to see the bark, especially on shrubs with dense canopies. Scouting for crawlers can be accomplished by placing double-sided tape or electrical tape with a thin film of petroleum jelly on branches near live scales. Mark the branches with flagging and check often for the tiny purple crawlers using a hand lens. Heavily infested trees should be removed to prevent spread of JMS to healthy trees. Lightly infested branches can be pruned out and bark could be scrubbed with a gentle brush and water to remove unsightly scales from trunks and branches.
As with other armored scales, timing of pesticide applications should coincide with crawler activity since the sprays cannot penetrate the adult scales' waxy, protective shell. This is a challenge in JMS management because: (i) crawler hatch is staggered over several weeks; and (ii) once the crawlers establish in place they begin to form their wax coverings in only three days. Therefore, the window of time for effective control is very narrow. Thorough applications of dormant oil at 2-3% in late winter are an important component of achieving successful control. During the growing season, horticultural oil at 2% can be applied but should target active crawlers and should not be applied to plants experiencing environmental stress. Recommended insecticides include the insect growth regulators pyriproxyfen (Distance) or buprofezin (Talus 70DF) and the neonicotinoid clothianidin (Arena 50 WDG). Horticultural oil (at 0.5 to 1 percent) can be tank-mixed with Distance or Talus 40SC for improved control. Continue to make applications on the recommended spray interval as long as crawlers continue to be trapped on the sticky tape, from mid-May through late-August.
Written by: Susan Scheufele and Nicholas Brazee