Several types of mites can cause damage to foliage; the most common are spider mites. These mites are capable of infesting many garden, tree, shrub and bedding plants found around the home. Mites are not insects, but arachnids, related to ticks and spiders. These eight-legged arthropods can be brown, red, green or cream-colored. They live in colonies, mostly on the lower surface of leaves. Adult females deposit small, red to cream-colored eggs on a leaf, bark, or in webbing. Webbing on the leaves of your plants is another sign of mites. Spider mite eggs usually take 4-5 days to hatch and adulthood is usually reached within a week, depending on how hot and how dry the air is. An ambient temperature higher than 85 degrees and a relative humidity of less than 60% produce optimal conditions for spider mite reproduction and maturity.
Because spider mites are very small, they can be difficult to see on plants. You can determine the presence of mites by holding a piece of white paper underneath a branch or shoot and shake or tap the branch sharply. If mites are present, some will be dislodged from the leaves and fall onto the paper, where they will be seen as tiny moving specks.
Small brown or yellow dots on the leaves of a plant are the most easily observed sign of a mite infestation. As feeding continues, the leaves turn yellow or bronze in color and drop off. Heavily infested leaves and branches can be enclosed in fine silken webbing. As feeding continues, the leaves turn yellow or bronze in color and drop off. On annual vegetable plants, the loss of leaves can have a serious, immediate impact on production.
Garden plants that are typically susceptible to mites are asparagus, beans, melons and squash, peas, tomatoes and strawberries. Some landscaped trees and shrubs that are often attacked are arborvitae, azalea, crabapple, rose, spruce and walnut.
Spider mites flourish on plants under stress. Keep plants well watered and fertilized, because damage is increased when the plant does not receive sufficient water.