If scale is present, the small, pale-colored crawlers will show up on the paper. Oystershell scale can be treated by spraying dormant oils after leaves drop in the fall, or before new leaves emerge in the spring. At these times, you also can scrape tree branches with a plastic, kitchen scubbing pad to remove eggs or you can prune heavily infested branches. For more information, see CSU Fact Sheet 5.513 . The caterpillars feed on new spruce needles usually starting at the top of the plant and moving down, thinning and discoloring the tree.
Heavy infestations can kill tree tops and permanently deform their growth.
The insect overwinters in eggs laid on or around the base of infested trees. This insect is most effectively controlled shortly after eggs hatch in late May or early June. Carbaryl, permethrin or acephate sprays are effective. Successful treatment is dependent on thorough coverage, but densely foliated spruce trees can be difficult to penetrate. For more information, see CSU Fact Sheet 5.542 .