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Spider Mites

Trees with spider mite damage

The spider mite is considered one of the most destructive spider mites in the United States. It injures the foliage of spruce, arborvitae, juniper, hemlock, pine, Douglas-fir, and occasionally other conifers. Dwarf Alberta spruce, Picea glauca ‘Conica’, is one of this pest’s preferred host plants. After hatching, the young, pale green mites called larvae resemble adults except they are smaller and have only three pairs of legs. As the mites mature, they shed their skins three times before becoming adults. Adults and nymphs have four pairs of legs and are dark green to nearly black with the body surface clothed with salmon pink-colored spines (Fig. 1). The adult’s legs are also salmon pink. This species damages host plants by sucking plant fluid from needles as they feed. Infested trees at first have a speckled, yellowish appearance, and lack rich green color. After prolonged feeding, needles turn rusty colored and may drop prematurely. Mites usually attack older needles located in the lower and inner parts of the plant. Damage may spread as the season progresses. This species also produces silken webs on the needles.