More than 50 plant species in Colorado are attacked by the oystershell scale. Of these, 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 overall appearance of the scale often is similar to that of the underlying bark and these Insects are easily overlooked.
Old scales can stay attached to the tree for several years before falling off.
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. Eggs from all the scale Insects do not hatch at the same time, and egg hatch may last a couple of weeks.