A Technical Report from The Bartlett Tree Research Laboratories 391
Oak species are used as the primary or secondary host by a large number of scale insects. High populations of any one of these insects devitalize host plants by sucking large portions of the sap. This is especially severe on plants that are under stress from deficiencies of light, water, nutrients, etc. The first symptoms of scale insect attack are small withered leaves, followed by tip dieback of small branches; then larger branches may die. This makes the plant more susceptible to attack by woodboring insects, diseases and winter injury. After a few years of heavy, uncontrolled infestations, younger trees may die, while larger ones become disfigured or distorted and lose their aesthetic appeal as ornamental plants.