WSU Extension

Hortsense

Arborvitae : Spider mites
(revision date: 3/10/2017)


Biology
Spider mites are tiny, eight-legged, and of various colors from yellowish or greenish to red. They may be found on the foliage and often produce a fine webbing on the branchlets or between twigs. Spider mite feeding results in a very fine yellowish speckling or stippling on the foliage, causing plants to appear discolored and unhealthy. Severe infestations cause leaves to turn brown and may weaken plants. Spider mite infestations are often worse during dry, dusty conditions.
Management Options

Non-Chemical Management
  • Hose mites from plants with a strong stream of water.
  • Conserve natural predators such as ladybird beetles, lacewings, and predatory mites. Avoid use of broad-spectrum insecticides which kill these beneficial predators.
  • High levels of nitrogen in the foliage encourage spider mite reproduction. Switch to a slow-release or low-nitrogen fertilizer.
  • Provide proper culture for plants. Healthy plants are more tolerant of damage, while drought-stressed plants are more susceptible.
Select non-chemical management options as your first choice!

Chemical Management

Apply pesticides at first sign of infestation, usually May to early June. Do not apply soap products to plants stressed by drought or when tender new foliage is present. Do not apply soaps in full sun or when temperatures exceed 90 degrees F. When using Safer Brand Insect Killing Soap Conc II, test a small area for sensitivity before application. 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: Arborvitae spruce spider mite damage
Photo by: C.R. Foss
Caption: Spruce spider mite adult
Photo by: A.L. Antonelli
Caption: Spruce spider mite damage
Photo by: R. Maleike
Caption: Spruce spider mite
Photo by: C.R. Foss