The spruce spider mite has the potential to be one of the most destructive conifer feeding spider mites in the United States and Canada. Adult female spruce spider mites will lay their brown, overwintering eggs beneath host plant bud scales, in the axils of needles, or beneath webbing on host plant branches or stems. Eggs are rounded, flattened from the top down, and have a thread (stipe) sticking up from their center. Larvae hatch from the eggs and develop into nymphs. Each process can happen in a matter of days; 3 days for larvae to develop and 6 days for nymphs to develop. The initial larva only has 3 pairs of legs. After it molts for the first time, 4 pairs of legs are present. Adult spruce spider mites are tiny, approximately 1/2 mm in length. They vary in color from dark green to brown. Adults legs are a salmon pink color. Each year, it is possible for 3-4 generations to occur; in some areas, 7-10 generations per year are reported. A single generation may be produced every 2-3 weeks. When the hot summer months arrive, the spruce spider mite enters a summer dormancy period until cool temperatures return in the fall. Spruce spider mites may be primarily dispersed via the wind.
The spruce spider mite may leave behind tiny strands of webbing on the needles of its host plants. As a result of spruce spider mite feeding, damaged needles on spruce hosts often turn reddish brown. Initial feeding may turn the upper surface of the host plant needle a stippled yellow color. This cool season mite is of most significance on ornamental landscape conifers, but may also occur in natural forests. Larvae, nymphs, and adults all feed on the host plant needle. Spruce spider mites often prefer to feed on older rather than new needles. Feeding often occurs in the lower branches, toward the inside of the tree. Damage occurs primarily in the spring and fall. If feeding is heavy, host plant needles may drop prematurely. This pest can reproduce quickly, in large numbers, and may suddenly cause very noticeable injury. Less active in hot, dry weather (typically midsummer). Certain climatic conditions favor spruce spider mites. Their populations have been found to respond favorably to 79°F temperatures and relative humidity between 50-60%; however, simulated rainfall on Fraser fir seedlings significantly limits spruce spider mite populations (Boyne and Hain, 1983).
Magnification is required to view spruce spider mite eggs. Tapping host plant branches over white paper may be a useful tool when scouting for spider mite presence. (View with a hand lens.) Do this as soon as any sign of off-green color appears on the foliage. Check 3-4 locations on the plant using this technique. If 10 or more spruce spider mites are found at each location on the plant, chemical applications may be necessary on high-value hosts.
Trees suffering drought stress should be provided with adequate watering to reduce the impact of spider mite feeding. Do not over fertilize trees infested with spider mites or piercing-sucking insect pests, as this can benefit the pests more than the tree itself. Syringing, or spraying mite infested foliage with a heavy stream of water, may help knock the spider mites off their host and provide management on ornamental/specimen trees or shrubs. If done on a regular basis (ex. weekly), syringing can have the same effect as strong rain events which help dislodge the mites and reduce the severity of their feeding.
Natural enemies of spider mites (Tetranychidae) can include pathogens, viruses, and predators. Phytoseiid mites, spiders, and insects (including some beetles, lacewings, true bugs, flies, and thrips) are also natural enemies of certain spider mites. Specifics regarding the spruce spider mite are not fully understood. However, Typhlodromus spp. may help reduce spruce spider mite populations (Marshall, 1986). A study looking at augmentative biological control of spruce spider mite on juniper using Neoseiulus fallacis and Galendromus occidentalis suggested that releases of predators may not be effective if spruce spider mite populations are currently high. During the trial, the cost of using the predatory mites was 2.5-7 times greater than chemical management options (horticultural oil or hexythiazox) conducted during the study (Shrewsbury and Hardin, 2003). The authors suggest that further research is needed to determine the efficacy and timing of early season predatory mite releases to provide optimal suppression of spruce spider mite.
Abamectin (NL)
Acephate (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Chlorpyrifos (N)
Chromobacterium subtsugae (NL)
Cypermethrin (NL)
Etoxazole (N)
Fenazaquin (NL)
Gamma-cyhalothrin (L)
Hexythiazox (NL)
Horticultural oil (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Metarhizium anisopliae (robertii) (NL)
Neem oil (NL)
Spinosad (NL)
Spiromesifen (L)
Tau-fluvalinate (NL)
Active ingredients that may be applied systemically include: Abamectin (injection), acephate (injection), Metarhizium anisopliae (robertii) (soil drench), and neem oil (soil drench).
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
