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Pest 411 Japanese maple scale infestations
Examine the bark
Japanese maple scale infestations
by Shimat V. Joseph and Will Hudson, Department of Entomology, University of Georgia
Fig. 1. Japanese maple scale.
Lorraine Graney, Bartlett Tree Experts
Identification
The adult males of JMS are winged, leave their waxy shell, and are not common. The wingless females are 2 mm long and remain under their waxy shell or cover (Fig. 1). The JMS females and nymphs are lavender-colored and found beneath their off-white oyster-shell shaped covers. Females are found primarily aggregate on the tree bark, at the base of branches and in the cracks and crevices on the bark (Fig. 2), although they are occasionally found on the leaves. Often, they blend in with the color and pattern of tree bark (Fig. 3) and are challenging to detect. Branch dieback symptoms appear when the trees are heavily infested.
Biology
A JMS female lays about 25 lavender eggs found underneath the female cover (Fig. 4). The eggs hatch into tiny pale purple-colored nymphs referred to as “crawlers” (Fig. 5). Crawlers are the only mobile stage with legs and antennae. They move around the tree bark and settle on suitable sites by inserting their piercing mouthparts. Once they settle and start feeding, they molt into the immobile nymphal stage and lose their legs and antennae. They develop into adults after molting through two more nymphal stages (3rd and 4th instars).
The Japanese maple scale (JMS), Lopholeucaspis japonica Cockerell (Fig. 1) is an insect pest of Japanese maple and several other ornamental tree species.
JMS-infested trees in the landscape reduce the value of the property. In the nursery, JMS infestation affects the marketability of the trees. This insect sucks the plant juices using its piercing and sucking mouthparts. JMS, similar to other armored scales, does not directly feed on the phloem vessels of the host tree and thus, it does not ingest an excessive amount of sugars and excrete excess sugars as honeydew. JMS secretes a detached waxy shell that covers the body.
Although males are present, females produce eggs without mating. Within a few months, the population size increases with large numbers of scales on the tree bark.
JMS completes two generations in North Georgia, with the first generation from April or May to August and the second generation from August into the following year. The JMS overwinter as nymphs on the bark. The late instar nymphs blend in with tree bark during the winter and easily go undetected. The overwintering JMS nymphs molt into females in early spring and become visible with a white waxy covering.
Host range
In addition to Japanese maple, JMS has been found on at least 17 other hosts such as Camellia, Carpinus, Cercis, Cladrastis, Cornus, Cotoneaster, Fraxinus, Gleditsia, Ilex, Itea, Magnolia, Malus, Prunus, Pyracantha, Pyrus, Salix, Stewartia, Styrax, Syringa, Tilia, Ulmus, Zelkova and others.
Monitoring
Because the nymphs and females of JMS infest the bark, bark ridge and collars, scouting these areas of the tree will help determine the JMS infestation. Often, the trunk of certain trees is hidden from view. The waxy coatings are clearly visible during the growing seasons, indicating infestation; however, it can be difficult to see them on light-colored barks.
The waxy shield covering the insect protects from external elements, including insecticide sprays. However, the crawler stage of JMS does not have this protective waxy cover. Thus, the crawler stage is more susceptible to insecticide sprays than other nymphal or adult stages and so it is critical to determine the peak emergence periods of crawlers.
Typically, the peak emergence of crawlers occurs in early spring for the first generation and mid-summer for the second. To this end, systematic monitoring of crawlers is necessary. Wrapping sticky cards or double-sided tape around the trunk can help determine crawler emergence activity (Fig. 6). The tiny, pale purple-colored crawlers get stuck to the edge of the sticky surface when they walk over, and they can be viewed using a 10× hand lens. Both generations will probably need control actions for effective management of this pest.
Management
Management of JMS will depend on the type of insecticide material being used. 4 Contact insecticides, such as horticultural oil and insect growth regulators are useful tools if adequate insecticide coverage on the JMS-infested bark is achieved. 4 Effective treatment can be challenging for some hosts as the bark is hidden by the tree canopy. Penetration can be improved by pruning out select branches. Systemic insecticides such as neonicotinoids can be used for JMS infestations in less accessible situations. 4 In the fall, the application of horticultural oil can cause substantial JMS mortality by dissolving the waxy covering and exposing them to cold winter conditions. 4 In the growing period, the use of 2-3% ultrafine oil can reduce the survival of the scales. The ultrafine oil is effective when applied above 40 °F. These sprays should target crawlers, and some IGRs will affect adult female egg viability.
Lorraine Graney, Bartlett Tree Experts (left), and Brian Kunkel, University of Delaware (right)
Fig. 2. Japanese maple scale infestation on truck and branches.
John .A. Davidson, University of Maryland, College Park Fig. 3. Japanese maple scales blend-in with the bark color and pattern.
Lorraine Graney, Bartlett Tree Experts Fig. 4. Female Japanese maple with purple eggs.
Brian Kunkel, University of Delaware.
4
Some neonicotinoid insecticides, such as dinotefuran, are effective against JMS as they move systemically within the tree. Both fall (root zone drench) and spring applications can be effective.
Robert Leckel, University of Florida Fig. 5. Purple-colored crawlers of Japanese maple. Fig. 6. Sticky tape wrapped around the stem.
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