CSU Extension Oystershell scale can be particularly difficult to control because they are protected with a waxy covering for most of their life. One popular control approach is the use of dormant oils. Several brands of dormant oil are available. These are typically used at rates of 2 gallons oil per 100 gallons of water.
Treatment is recommended late in spring on warm days before bud break.
Effective use of dormant oils requires thorough coverage of infested trunks and branches. Where heavy crusts of scales exist, control will be reduced. After leaves have emerged, oystershell scale is vulnerable to control only during the crawler stage. After the waxy covering is produced by the insect, it is not susceptible to control with insecticides. Determination of when the crawler stage is occurring requires a careful examination of the plant for the presence of the crawlers.