There are several different species of mites that can cause damage to a wide variety of ornamental plants, including deciduous trees and shrubs, evergreens, and garden plants. As the name implies, mites are so small that they often cannot be seen without the aid of a magnifying glass, which makes identification difficult. Often the first sign of a problem is extremely fine webbing produced by certain species of mites. More commonly, an infested leaf or needle will begin to lose its normal green color, followed by a flecked or stippled pattern. To verify the presence of mites, place a piece of white paper beneath an infested branch and gently shake the foliage. Mites will fall and appear as slow-moving specks on the paper.
Mites are not insects but tiny animals related to spiders. Mites feed by using their needle-like mouthpart to pierce the chlorophyll-bearing cells of a plant leaf and suck out the plant juices. This repeated feeding action will produce a flecking, bleaching, or stippling pattern on the affected foliage. When significant populations are present, these injured areas can enlarge, turn yellow or brown, dry, and then drop from the plant. Infested deciduous leaves can become deformed or curl downward.
Although mites can appear any time during the growing season, most mite populations will increase quickly during hot, dry weather. Their development from egg to adult usually takes less than a week, and most mite species produce several generations each season. This combination of rapid growth and multiple generations makes them difficult to control.