Hemlock: Hemlock scale
Photo by: R. Van Denburgh
Biology
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
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
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: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- 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
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.