oyster shell scale
chiefly North American
noun
1Any of several scale insects mainly of the genus Lepidosaphes, especially L. ulmi, which attacks many trees and shrubs, including commercial fruit and hardwood trees (also called mussel scale).
2The disease caused by such insects, characterized by small curved scales on the plant's bark.
Origin
Late 19th century; earliest use found in Report of the Vermont Board of Agriculture.