Spider Mites

What Are Spider Mites?

Spider Mites can be a major problem on many woody ornamental plants. Feeding by spider mites causes discoloration, dirty appearance and early leaf drop. Spider mites are related to spiders, having eight legs. These pests are extremely small and are difficult to detect unless viewed with a 10X hand lens. Dormant periods are spent as adult females in protected places (plant or mulch debris) or as eggs. Under appropriate conditions adults resume activity or eggs hatch. Many generations can occur over a single season. Adult females can live for several weeks, laying many eggs daily. Mite development, from eggs to adults, occurs within days, which accounts for rapid build up of large damaging populations on plants.

How Spider Mites Cause Damage

Spider mites have needlelike mouth parts, which pierce cells and suck fluids out. The feeding action causes fine stippling or flecking of foliage. With large mite populations on plants, entire leaves can become yellow or bronze. Presence of shed skins, eggs, and mites give the foliage a dirty appearance. Sometimes, spider mites will spin very fine webs on the plant. These webs are not the coarse webbing produced by common garden spiders. Damage caused by spider mites not only affects the appearance and aesthetic value of the plant, but also its health and vigor. Early leaf drop can occur with some mite-infested plants.

Checking for Spider Mites

To check for the presence of spider mites, hold a white piece of paper under a branch. Shake the branch to dislodge mites onto the paper. If present, these specks will begin to move after a few seconds.

Plants Vulnerable to Spider Mites

Plants commonly damaged by spider mites include: arborvitae, azalea, beech, birch, boxwood, citrus, elm, euonymus, hemlock, holly, honey locust, juniper, maple, Mexican orange, pine, pyracantha, oak, redwood, rose and spruce.

Controlling Spider Mites

• Early detection and treatment is the key to control.
• Once populations build to damaging levels, control is difficult.
• Spray coverage of both leaf surfaces as well as stems is critical for mite control.
• Horticultural oils will help, applied both dormantly and in-season.
• For mites that do not overwinter on host plants, dormant oils may not work.
• Several applications of miticides may be necessary.