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Spruce Spider Mite

April 26, 2000

Spruce spider mite, Oligonychus ununguis,eggs have hatched now throughout the state. This hatching was observed during the first week of April in northeastern Illinois by Don Orton, Illinois Department of Agriculture. Now is the time to make spray applications before the mites have caused serious damage. Spruce spider mite is a cool-season mite in contrast to two spotted spider mite, Tetranychus urticae, which is a warm-season mite. Spruce spider mite feeds on coni-fers such as spruce, arborvitae, hemlock, juniper, Douglas fir, and some pines. They use their piercing–sucking mouthparts to remove plant fluids and chloro-phyll (green pigment). Injured foliage will generally appear bronze colored to brownish.

Adult mites are oval-shaped and approximately 1/60th of an inch long. Adults are black or tan, whereas the nymphs are light gray-green in color. Eggs, which are round and brown in color, are laid under bud scales or in the axils of needles. The overwintering eggs are laid on plants from September through November. These eggs hatch into nymphs. Spruce spider mites are present in high numbers from April through mid-May, although they are usually present into June in northern Illinois. It generally takes three to six days to go from egg to nymph. All motile or active stages primarily feed on needles, generally preferring older needles. There can be three generations per year.

Spruce spider mite presence can be verified by knocking them off branches onto a white sheet of paper where they are easily seen. They produce a green streak when smeared. Red streaks on the paper are indicative of predatory mites.

Management of spruce spider mite involves imple-menting proper cultural practices such as watering to minimize stress and the use of pest control materials. Pest control materials that may be used to manage spruce spider mite include bifenthrin (Talstar), dicofol (Kelthane), dimethoate (Cygon), summer oil, or insecticidal soap. Because these materials only work by contact activity, it is important to get thorough coverage. Be careful when using summer oils on blue-needled conifers as they may cause discoloration.

Author: Raymond Cloyd


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