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