Calico scale—Eulecanium cerasorum
This soft scale (family Coccidae) can occur on many deciduous trees, usually on well-shaded plant parts. Liquidambar is the preferred host in California. Occasional hosts include apricot, box elder, maple, plum, and walnut.
The mature female is globular and about 1/4 inch in diameter. Living adult females have mottled (calico) coloration; they are black or dark brown with four rows of white or yellow blotches. Small patches of woolly wax can occur on the pale spots. The nymphs are dark brown, flattened, and covered with thick, elevated, plates of pale wax.
Calico scale develops through three life stages: egg, nymph, and adult. Overwintering is as second instars, which in late winter mature into adult females that lay eggs beneath their body. During spring the eggs hatch into crawlers (mobile first instars), which move to settle and feed on leaves. Nymphs molt to the second instar during summer. In the fall, the second instars move to overwinter on twigs. There is one generation per year.
Scale nymphs and adult females suck phloem sap from twigs. While feeding they excrete sticky honeydew on which grows blackish sooty mold. Low populations are not damaging to plants, but liquidambar (the host preferred in California) may decline if the scale is abundant during several consecutive years.
Calico scale is rarely abundant enough to warrant control, except on liquidambar. If this soft scale is damaging hosts or its honeydew is not tolerable, infested branches and shoots can be thoroughly sprayed with horticultural oil during the dormant season, except not on plum and walnut which may be damaged by dormant-season oil. Oil is also effective if sprayed when monitoring indicates that crawlers are active in the spring. See the section "Monitoring" in Pest Notes: Scales for how to effectively time oil application. Consult Pest Notes: Scales for more management information.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Adult female calico scale.
Adult female calico scales.
Size of adult female calico scale.
Second instars of calico scale.