Pest Name: Spruce Spider Mite

Background: The spruce spider mite is considered one of the most destructive spider mites in the United States. It injures the foliage of spruce, arborvitae, juniper, hemlock, pine, Douglas-fir, and occasionally other conifers. Dwarf Alberta spruce, pictured above, is one of this pest’s preferred host plants.

Damage: This species damages host plants by sucking plant fluid from needles as they feed. Infested trees at first have a speckled, yellowish appearance, and lack rich green color. After prolonged feeding, needles turn rusty colored and may drop prematurely. Mites usually attack older needles located in the lower and inner parts of the plant. Damage may spread as the season progresses. This species also produces silken webs on the needles.

Monitoring: When plant foliage begins to show off-green, or stippled, color and spider mites are suspected, perform a foliage check. Take a piece of white paper, hold it under a branch suspected of having mites, and strike the branch hard against the paper. This should dislodge the mites, and even though they are only 0.5 mm long, you should be able to see the dark, oval spider mites against the white background. Examine three to four places around the plant. If you dislodge ten or more mites at each site, it would be advisable to apply a registered miticide according to label directions.

Treatment: There are several options for treating Spruce Spider Mites:

  1. Insecticidal Soaps or Horticultural Oil.

  2. Neam Oil.

  3. Pyrethoid based pesticide.

  4. Apply a Dormant Oil spray in mid winter to kill overwintering eggs.

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