Pest description and crop damage Hemlock scale feed on the needles of Eastern hemlock (Tsuga canadensis) and spruces (especially Colorado blue). Adult scale are round to oval, dark gray or black, and about 2 mm (0.1 inch) in diameter. Immature scale (crawlers) are green to yellow. Scale typically are found as small bumps on the underside of needles.
Scale feed on the needles by sucking out the cell contents. The initial symptom of infection is yellow spots on the upper surface of the needles. As few as 4 to 6 scale per needle will cause the needle to drop. Colorado blue spruce in particular loses large numbers of needles. Severe infestations may weaken trees sufficiently to cause death. The hemlock scale is most common on stressed trees.
Apply to control the early summer crawler stage.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 102).