Oystershell scale attacks a wide range of plants.
The scale got its name because it resembles an oyster shell. It is found in every state but it is found more often and in heavier numbers in the northern states. The scale often blends in with the color of the plant's bark. The scale is often "discovered' because branches are dying back from the feeding injury.
Oystershell scale is an armored scale (its covering is a hardened waxy material). There are two commonly found races of oystershell scale in Illinois. They are brown oystershell scale and gray ostershell scale. The scale overwinters as eggs under the mother's covering. Crawlers of the brown race occur on dogwood when Vanhoutte spirea is in full bloom (about mid June in Northern Illinois). The crawlers of the gray race, which feeds on other hosts, emerge later.
Crawler sprays of chemical insecticides timed to coincide with egg hatch are effective. This insect is not controlled with dormant oil applications. Pruning severely damaged areas will reduce infestations.