Spruce Spider Mite

    Spruce Spider Mite

    Oligonychus ununguis

    spruce spider mite

    Adult spruce spider mite and eggs (Ward Strong, BC Ministry of Forests, Bugwood.org)

    spider mite webbing

    Spider mite webbing on spruce needles (Petr Kapitola, Central Institute for Supervising and Testing in Agriculture, Bugwood.org)

    spruce spider mite damage

    Spruce spider mite damage (John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org)

    Pest Description

    • adults: very tiny, ~ 1/64 inch; dark brown/reddish to dark green
    • eggs: smaller than adults and are brown to red

    Host Plants, Diet & Damage

    • all conifers, especially blue and Alberta spruce in Utah
    • feed on needle cell contents
    • cause yellowing/stippling; needle browning and dieback
    • may cause premature needle drop
    • fine webbing on needles; dirty appearance
    • damage may be patchy within canopy
    • prefer older growth

    Biology, Life Cycle & Damaging Life Stage

    • overwinter as eggs near needle bases
    • egg hatch begins around mid-March to mid-April
    • cool-season mite, active primarily in spring and fall
    • overlapping life stages present in late spring
    • over-summer primarily as eggs; dormant in summer at temperatures warmer than 80-90 degrees F
    • a single generation takes 2 to 3 weeks; up to six generations per year are possible
    • can disperse via the wind
    • immatures and adults are the damaging stages

    IPM Recommendations

    • Manage trees to improve or maintain health.
    • Monitor spider mite populations on host plants with a “paper test” starting after budbreak. To conduct the test, hold a white sheet of paper under affected branches and shake vigorously. Tiny specks moving around on the paper indicate the presence of mites.
    • Preserve beneficial mites and organisms.
    • Apply a dormant horticultural oil or insecticidal soap to needles and twigs in spring or fall when mites are present.
    • Apply an insecticide/acaricide (bifenazate; horticultural oil; insecticidal soap; pyrethroid) when mites are present on leaves.