Spider mites are common pests for a wide variety of landscape plants, trees and shrubs. Most mites are active during warm, dry months, but there are cool season mites that infest trees during the winter. Most spider mites and their newly hatched eggs can tolerate freezing temperatures without perishing.
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Spruce spider mites are cool season mites that infest conifers, such as Fraser fir. These pests thrive in colder temperatures and become less active when the weather is hot. Spruce spider mites are members of the arachnid family that have eight legs and soft bodies. These pests are usually red or green in color, and they lay their eggs on tree shoots. The spruce spider mite is not found on host trees during freezing weather, but their eggs remain there until it is time to hatch. The twospotted spider mite is also a common pest in a variety of trees. These mites are considered a warm season mite, but according to the University of Florida, they often survive freezing weather when infesting greenhouse-grown plants. Twospotted spider mites are very tiny and are typically brown, orange, red, yellow or opaque. These mites have two large spots that are visible on their bodies.
All spider mites feed on host plants with piercing or sucking mouthparts. As they feed, they remove plant sap from host trees, causing leaves to turn yellow and appear bronzed. Heavily infested trees can eventually die. Most spider mite species place a fine silky webbing over the leaves and branches of host trees.
Spruce spider mites are susceptible to predatory insects, such as lacewigs and lady beetles. Spruce spider mites reproduce the fastest during the warm months, but they can survive and function in temperatures that are below freezing. Twospotted mites can also be controlled by predatory insects and survive best in freezing temperatures when infesting greenhouse-grown plants. Spider mites are more easily controlled during periods of rainy weather because the rain knocks the mites from their host plant.
Both spruce spider mites and twospotted spider mites are most difficult to control at the egg stage. During the growing season, spider mites can occur on host trees in all stages of development. Pesticides are available at your local garden center for spider mite control. However, pesticides also kill predatory insects which may cause a rise in spider mite populations. Miticides are available for spider mites in all stages of development, but some mites can become resistant to miticides if used on a regular basis.