Oligonychus Ununguis

Photo courtesy of USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org

Signs & Symptoms

Photo by Sandy Gardosik, Pennsylvania Dept. of Agriculture (PDA).

  • Rusty or bronze colors near the base of the needles; damage possibly most severe during hot, dry weather
  • Premature needle drop
  • Damage heaviest at the bottom, inside of the tree
  • Permanent chlorophyll loss
  • Fine webbing at base of needles and twigs; cast skins, dead mites, dirt, and other debris trapped in the silk

Where to Look

Photo by Chal Landgren, OSU.

  • Localized areas in the field
  • Along dusty roads and/or where other insecticides have been used

Similar Symptoms As

  • Eriophyid mites
  • Environmental stress
  • Aphids

Scouting

  • Use a 15-20X hand lens to view spider mites and eggs. Eggs have a single, hair-like stripe on the top, which can be used to distinguish them from other spider mite eggs.
  • Look for eggs during the winter and early spring (before April).
  • Look for damage about halfway up the canopy and in the interior part of the tree.
  • To detect active stages, beat suspect branches above collection tools, such as paper plates or any light-colored sheet or surface.

Management Options

  • Based on scouting, decide whether to control.
  • If eggs are found in February or March, consider an application of horticultural oil.
  • Miticides typically are applied in May or early June; however, exact timing depends on scouting.

Host Susceptibility

host susceptibility graph

  • High susceptibility: Fraser fir
  • Medium susceptibility: Grand fir, Noble fir
  • Low susceptibility: Douglas-fir

Management Calendar


  • Look for foliage yellowing and bronzing: Mid-May through Octoberr
  • Look for overwintering eggs: February through March
  • Look for active mites: April through October
  • Spray eggs (if needed): February through March
  • Spray miticide (if needed) for adults/immature mites: May through June