Conifer Spider Mites

Spider mites infest a variety of conifer species, including pines, spruce, hemlocks, arborvitaes and others. The mites pierce and suck nutrients from conifer needles.  

Because spider mites are so tiny, the easiest way to diagnose infestation is to take a twig sample from your conifer and beat it against a white piece of paper; the spider mites will appear as moving brown specks on the paper.  Spider mites create webbing at the base of needles and branches.

Download Pest Sheet




  • Common Symptoms
    • Needles will become mottled in color. This will progress into needle discoloration and in severe infestations, needle loss.

    • A properly timed injection of ACE-jet can significantly reduce or eliminate the existing population of mites on the tree.

    When To Treat
    • ACE-jet should be applied at the first sign of mite feeding.

      Since spider mites prefer hot and dry conditions, and infestation usually becomes a severe issue in the summer months. We recommend a program of monitoring environmental conditions during the summer months: during periods of summer stress, inspect trees for building mite infestations, which are particularly injurious to conifers. In other words, keep one eye on the trees and another eye on the weather.

    What To Expect After Treatment
    • Treatment with ACE-jet will quickly kill the mites present. However, ACE-jet has limited residual value and may require more than one application to protect against re-infestation.

    References And Photo Credits
    • Main photo taken by Rayanne Lehman, Pennsylvania Department of Agriculture,
      Mite infestation on spruce 1 taken by USDA Forest Service – Region 4 – Intermountain Archive, USDA Forest Service,
      Mite infestation on spruce 2 and 3 taken by John A. Weidhass, Virginia Polytechnic Institute and State University,