Damage

Mites are not insects, but tiny animals related to spiders. Mites feed by using their needle-like mouthparts 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. When mite populations are high, extremely fine webbing is produced by certain species of mite.

Life Cycle

The two-spotted spider mite overwinters as adult females in ground litter or under tree bark. The adult has four pairs of legs. The body is greenish and marked by two spots on the back. When temperatures warm in spring, the females become active, feeding and laying eggs. The female will live about two to four weeks and during this time will produce from 100 to 300 eggs. The two-spotted spider mite is more prolific in warm to hot weather, and multiple generations will be produced during the growing season.

The spruce spider mite overwinters as eggs under bud scales of needles, and under webbing on stems and branches. From the time the eggs hatch in early spring, successive populations develop at 2 to 3 week intervals, with three or more generations possible each year. Spruce spider mite prefers cooler weather and is primarily a problem in spring and fall, when it will feed on the older rather than newer needles of the host plant. A small, oval-shaped mite, it is light gray-green when young, turning dark green to black as it matures, although colors can vary.

The European red spider mite overwinters as eggs, which are often laid in such large quantity that the twigs and branches appear to be covered with a fine red brick dust. Eggs begin to hatch in early spring with as many as seven generations produced each year. Adults are reddish-brown and oval-shaped with four rows of spines on the back.

Management

Cultural Management

The presence of a few mites on a host plant usually does not warrant enough concern to require any kind of control. The accumulation of dust and dirt on foliage tends to provide a favorable environment for many mite species, so periodically hosing the plant down with a strong stream of water will effectively remove or reduce the population. Maintaining healthy, vigorous plants is a preventative measure in keeping mite populations low. Avoid over fertilizing, as this can be beneficial to mites. Closely monitoring the extent of any damage and the size of the mite population will help determine whether further steps are required.

Biological Management

Some species of mite are held in check by the presence of predatory mites and insects, but this balance can be upset when the plant is under stress from improper siting, drought, or other environmental conditions.

Chemical Management

When infestations are severe enough to warrant more extensive management, thoroughly spray the foliage with an appropriate miticide, paying particular attention to the undersides of leaves and needles. Because mites have a rapid growth cycle and are capable of producing several generations per growing season, repeated applications of chemical controls may be necessary.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).