integrated pest management

Mites of Ornamental Plants

Mites differ from insects in that they have 8 legs and 2 body regions whereas insects have 6 legs and 3 body regions. There is one exception however, young mites or nymphs have only 6 legs in their early stages and gain the 4th pair of legs as they mature. Mites also vary greatly in color as their appearance is a function of the host plant on which they are feeding. Most of the coloration of spider mites results from the accumulation of food material and waste in the body. Consequently, coloration is more pronounced just prior to molting in nymphs and in more mature adults.

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Leaf Blister Mite Damage on Pear
Figure 1. Leaf Blister Mite Damage on Pear

The spruce mite is quite small (1/60 inch) and usually a dark reddish color. In some cases, the mite may be dark green. The legs and front part of the body are buff or tan colored. Large quantities of "spider-like" webbing are usually produced during feeding the process. European red mites are bright to brownish-red and unspotted. The body is quite elliptical in outline and about 1/75 inch in length. There are four rows of long curved spines down the back, each borne on a whitish tubercle. The two-spotted spider mite is about 1/60 inch long and ranging in color from pale yellow through green to brown to orange. The male is smaller with a narrower body and pointed abdomen. Two dark spots, composed of food contents, show through the transparent body wall. The mites are oval in shape and sparsely covered with spines.

Life History
Most mites have a similar life cycle however, certain species overwinter either as eggs or adults. The spruce and European red mites overwinter as eggs while the honeylocust spider mite overwinters as a mature female. The overwintering sites vary (ie. spruce mites and two-spotted spider mites on the foliage, honeylocust spider mites in bark cracks and crevices of the host plant and European red mites on twigs and smaller branches). Once mites hatch from the egg, they begin feeding on the foliage rupturing the cells and withdrawing the contents. The result is the presence of tiny chlorotic flecks and a bronzing of the foliage. Extensive feeding will result in stippling, and a yellow and white cast to the leaves.

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European Red Mite Damage on Apple
Figure 2. European Red Mite Damage on Apple

Mites are very prolific and populations can build up quite rapidly. Most mites are active throughout the growing season, however the spruce spider mite is a cool season mite and is more prolific in late spring/early summer and late summer/early fall. During hot dry weather, they tend to hibernate. However, the damage caused by their feeding usually coincides with the first hot dry spells of summer.

Damage from mite infestations can be quite pronounced and significantly reduce the vigor and growth of affected plants. Webs are usually present as well as a graying of the foliage particularly on evergreens. Close examination of the needles and webs reveals tiny flecks or particles which are usually the mites themselves. Holding a light sheet of paper under a branch and shaking the branch vigorously will dislodge them and facilitate a correct diagnosis.