Needled Evergreen Shrubs: Needles

Mites of Evergreens

Spruce spider mite damage appears as tiny yellow stipples on needles. The needles turn yellow, and then brown. The damage is usually first observed on the older needles at the base (or one side) of the tree (or shrub), eventually moving up the tree (or shrub). When the mite population is very high, webbing may be noticed on the needles. Lower branches may lose all of their needles, except new growth on spruce. Small trees and shrubs may be killed and large trees may have some dieback. This spider mite prefers cooler temperatures and is active in the spring (March - June) and fall (September - November). There are other species of mites that attack juniper. The damage is similar to spruce spider mites, but occurs throughout the summer. Spider mites are very tiny, about 2 mm. They have 8 legs and are yellowish green when young. When mature and fully fed they are grayish black, with a tan area behind the mouthparts. The eggs are circular and reddish brown. There are several generations a year and eggs overwinter on the bark and needles. This mite prefers spruce, pine, hemlock, and arborvitae, but will attack other conifers. To check for mites on a pine, tap branches over white paper and look for the dark slow moving mites. Also look for predator mites, which are fast moving, and tiny round, black ladybeetles that feed on the mites.

Management: If more than 10% of the tree is damaged and no predators are found, control may be needed. Use a dormant oil in winter to control overwintering eggs, if they are abundant. (They may be seen clearly with a hand lens.) During the growing season, a summer rate of horticultural oil or insecticidal soap may be used.

Rust mites cause yellowing and dropping of needles on hemlock, fir, spruce, yew golden-larch and pines. These mites are eriophyid mites, which are very tiny . At 10X magnification, they are visible as light yellow, spindle-shaped forms with four legs. On hemlock, the hemlock rust mite feeds on the upper and lower surfaces of the needles. On pine, rust mites are usually found between the needles within the needle sheath.

Management: Use a horticultural oil spray at the first sign of mite activity and damage unless predators are obvious and mite populations are low.

Keywords: spruce spider mite, spruce spidermite, spider mites, rust mites, eriophyid mites, hemlock rust mite

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Photo Gallery

Close-up of spruce spider mite.

Mite eggs on hemlock.

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