Hemlock: Hemlock scale

categories: Conifers Hemlock Hemlock Insects Ornamentals

revision date: 2024-07-10 01:44

shown on purple background these hemlock needles are gray colored and dying.
Hemlock scale
Photo by: R. Van Denburgh


Hemlock scales feed on the needles of Eastern hemlock (Tsuga canadensis) and spruces (especially Colorado blue). Adult scales are round to oval, dark gray or black in color, and about 2 mm (1⁄10″) in diameter. Immature scales (crawlers) are green to yellow. Scales are typically found as small bumps on the underside of needles. As few as 4 to 6 scales 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.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Provide proper culture. Healthy plants are less likely to be infested and more tolerant of damage.
  • Prune and destroy branches with heavy, isolated infestations (when practical).

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

  • Oils are effective in early spring.
  • Apply all products (excluding oil and dormant sprays) to control the immature crawler stage in early summer.
  • Homeowners should not make foliar applications to trees over 10 ft tall.
  • Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.