Sycamore scale—Stomacoccus platani
Sycamore scale (Steingeliidae) feeds only on Platanus spp., such as London plane and the native California sycamore, P. racemosa.
Identification
Sucking feeding by the scale causes numerous, small, yellow spots on leaves. Infested leaves can become distorted, discolored, and may drop prematurely.
Anthracnose and powdery mildew fungi also commonly cause discoloring and premature drop of sycamore leaves. Distinguish sycamore scale by the tiny, discolored leaf spots it causes and by the scales' cottony wax, especially on bark.
The insects themselves are brown or yellow and less than 1/12 inch long. Except for the crawler stage, sycamore scale does not resemble most other scales. Adults resemble immature (wingless) thrips. The nymphs and resting-stage preadults, called cysts, are elliptical and resemble insect eggs or tiny footballs. During certain stages, nymphs produce whitish wax and resemble whitefly pupae. Male cocoons, mature females, and egg masses can also be covered with cottony white tufts.
Sycamore scales can occur on foliage from leaf flush through fall and on tender bark anytime of year. They overwinter on and beneath bark, where eggs hatch during late winter. The crawlers (mobile first instars) move from bark to feed on leaves. Some scales develop on bark or move between leaves and bark during summer.
Damage
Sycamore scale causes small, yellow spots on leaves. Infested leaves can become distorted and stunted and may turn brown and die or drop prematurely. Prolonged high populations of the scale can stunt tree growth and cause dieback of twigs and small branches. On young trees, infestations can cause abnormal bark roughening and sloughing off of bark.
Solutions
Provide appropriate growing conditions and cultural care and protect trees from injuries. Healthy trees are better able to tolerate pest damage, such as premature leaf drop. Lady beetles that feed on sycamore scale include the twicestabbed lady beetle and Exochomus quadripustulatus, which is black with four orange to yellow blotches.
Foliar sprays are not recommended because trees are often large and it is difficult to thoroughly wet the underside of leaves where scales feed. If scales were abundant the previous season and damage cannot be tolerated, apply narrow-range oil or another insecticide during bud break. For more information, see Pest Notes: Sycamore Scale and The Scale Insects of California Part 2: The Minor Families . |
Distorted, spotted leaves
Scale eggs, nymphs, and wax
Adult female sycamore scale
Male (top) and preadult (cyst) female
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