Includes Parthenolecanium corni
Pest description and damage Scale insects are small (less than 0.125 inch in length) soft insects that live beneath waxy scales. These insects are often identified by the shape and size of their scales, the description of adult males and females, immature crawler stage, color of eggs, and host plant preferences. Lecanium scales are most noticeable as the female scales expand in size in the spring. As females swell in the spring, they produce large egg masses under their scales and release considerable honeydew that coats nearby foliage. The female lecanium scales are about 0.13 inch in diameter and vary from red to dark brown in color. They are oval and resemble small "helmets," "turtles," or bumps on branches and stems. Male scales are smaller, flat, and oblong. Crawlers are pale yellow and overwinter on stems.
Biology and life history Lecanium scales overwinter as immatures on twigs and branches. They resume feeding in the spring and begin to swell; the males, when mature, escape from beneath the scale, and fly to find females. The fertilized female swells to a hemispherical shape and eggs are laid underneath the scale in May-June. The females are initially soft and exude honeydew, then harden. The eggs remain under the scale until hatching in early summer. Newly hatched yellowish-brown crawlers congregate on small branches, twigs, and the undersides of leaves. When infestations are heavy, crawlers are found on the upper surface of leaves, and on the fruit. Young scales are dispersed by wind, rain, irrigation, or by people and machinery. After four to six weeks on the leaves, the young return to the stems and twigs to feed and overwinter. There is one generation per year.
Pest monitoring Inspect twigs during the dormant season for flat pale-yellow scale crawlers. Pay attention to weak plants. In late spring, examine beneath any hemispherical females to determine if eggs are still present (tiny beads roll out from beneath the scale) or have hatched (white fluff beneath the scale). The new crawlers are detected, using black tape with sticky side out on twigs near old scales, in May. Crawlers are best observed through a 10X magnifying glass.
Management-cultural control
Remove or squash swelling scales in the spring when they are just starting to mature or prune out heavily infested branches.
Management-biological control
Several predatory mites and parasitoid wasps feed on these scale insects. Check beneath scales for predator mites or wasp grubs to determine mortality. Holes in the top surface of scales indicate that parasitoids have already emerged.
Management-chemical control
See Table 1 in:
Chemical Control of Landscape Pests
For more information
See "Scale insect" in: