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Oystershell scale

 Image of Oystershell scale

The oystershell scale is one of the most common armored scale insects that cause injury to shade trees and shrubs. Ash, cotoneaster, dogwood, lilac, poplar and willow are most commonly infested. Oystershell scales attach themselves to the bark of twigs and branches. They feed on the plant by sucking out plant sap and can weaken and even kill the plant when the infestations are abundant.

The most familiar stage of the oystershell scale is the covering of the full-grown female scale that overwinters attached to the bark. The mother scale is about 1/8-inch long, brown or gray, slightly banded, and the general shape of an oyster shell.

The oystershell scale overwinters in Colorado only in the egg stage. Eggs are underneath the old scale covering of the mother. At lower elevations, eggs typically hatch in late May or early June. At higher elevations, egg hatch may be delayed into mid-June.