WSU Extension

Hortsense

True Fir : Spruce spider mite
(revision date: 3/22/2021)


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

Biology
The presence of spruce spider mites is indicated by yellow or bronzish stippling beginning near the needle bases. Infestations usually begin on older needles of the lower branches and spread upwards as the mite population increases. Damaged needles eventually turn brown or reddish-brown. Fine webbing can cover the needles and twigs. The actual spider mites are very small and vary in color from greenish to orange, dark green, or black, with orange legs. Spruce spider mites attack many species of conifers. They are easily spread by wind and are often worse on dusty roadside trees.
Management Options

Non-Chemical Management
  • These mites are probably controlled naturally by predatory mites and rain.
  • Try to avoid broad-spectrum insecticides that will kill predatory mites and insects and allow a spider mite population explosion.
  • Hose trees with strong stream of water to wash off spider mites (where practical).
Select non-chemical management options as your first choice!

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

Begin monitoring for spider mites in the late spring or especially during hot weather. Soaps should be applied in May or early June if mites are present. Repeat application may be necessary. 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.
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium salts of fatty acid  |  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