Crabapple: San Jose scale

categories: Crabapple Crabapple Insects Ornamental trees Ornamentals

revision date: 2022-11-22 10:33

Closeup of San Jose scale.
San Jose scale closeup
Photo by: K. Grey

Biology

San Jose scale is an armored (hard) scale found on many deciduous trees and shrubs including (but not limited to) apple, cherry, elm, maple, poplar, and willow. The scale insects are about 1/16″ in diameter. The female is gray with a yellow spot in the center. The crawlers are yellow and are easily spread by wind, birds, or people. San Jose scale may be found on twigs, branches, leaves, and fruit. Heavily infested trees may wilt and appear water-stressed. Severe infestations may cause twigs and branches to die back. The scale overwinters as black immature scales.

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 plant care. Healthy plants are more tolerant of insect damage.
  • Prune and destroy localized infestations.
  • Natural predators and parasites help control scale populations, but may not prevent damage in severe infestations. Avoid use of broad-spectrum insecticides which kill beneficial insects.
  • By late April, begin monitoring for crawlers by using double-sided sticky tape.

Chemical Management

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

  • Pesticide recommendations are for flowering (non-edible) crabapples.
  • Apply early spring to smother overwintering scale.
  • Apply oils during delayed dormant period.
  • 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.

Additional Images