WSU Extension

Hortsense

Juniper : Spruce spider mite
(revision date: 3/10/2017)


Biology
Foliage of plants infested with spruce spider mites is often speckled, stippled, or bleached-looking. Severely damaged leaves or twigs may drop. Some species of spider mites produce fine webbing on the plant. They may be a problem to control because of the dense foliage typical of ornamental junipers. These mites are extremely small and are easily spread by wind, birds, and people. They overwinter as eggs on the host and can begin hatching as early as April or May.
Management Options

Non-Chemical Management
  • Predaceous mites and insect predators such as ladybird beetles may naturally control spider mite levels. Avoid use of broad-spectrum insecticides that kill these predators.
  • Wash spider mites from plants with a strong stream of water.
  • Keep plants healthy to increase pest tolerance.
  • Switch to slow-release or lower-nitrogen fertilizers. High levels of nitrogen in the leaves can increase spider mite reproduction rates.
Select non-chemical management options as your first choice!

Chemical Management

Begin monitoring for spider mite in the late spring or especially during hot weather. 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.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
Images
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Caption: Spruce spider mite adult
Photo by: A.L. Antonelli
Caption: Spruce spider mite damage
Photo by: R. Maleike