Spider mites are a common pest of many trees, shrubs and plants. They are difficult to detect because of their size. At first glance, they look like small, moving dots. What they lack in size, they make up for in numbers. Spider mites reproduce rapidly and populations can grow quickly. High levels of infestation can stunt a plant's growth and even contribute to death of the plant.
Part of the Tetranychidae family, mites are arachnids - not insects. Common examples include the two-spotted spider mite, southern red mite and the spruce spider mite. They have needle-like mouthparts, which they use to pierce the leaves or needles of host plants and suck out the fluids from individual plant cells. Spider mites are known to feed on hundreds of plant species.
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Spider mites are pervasive and can be found in most geographies. Infestations are particularly common in summer when the weather is hot and dry, favorable conditions for mite reproduction.
Most spider mites overwinter as eggs on leaves, needles or bark, though the two-spotted spider mite overwinters as an adult. They hatch at various times depending on the species with feeding activity occurring virtually any time from spring through autumn. They develop through five stages from egg to adult. The immature stages appear similar to the adults, only smaller. An adult female may lay many dozens of eggs and, under the right conditions, eggs can develop to adults in a week or less. That means many generations can occur in a short timespan with populations quickly increasing to damaging levels. This is especially true during hot weather.
As spider mites injure foliage through their feeding, the leaves develop a stippled or speckled appearance with pale spots where plant cells have been depleted. The infested plant may become discolored or bronzed with scorching developing on the leaves. Spider-like webbing is another common, and more easily spotted, sign of infestation.
Spider mites cause minimal damage when populations are low so one of the best ways to minimize injury to plants is to keep their numbers in check through frequent inspections for the pest and its eggs. Additionally, since spider mites thrive on stressed plants, trees and shrubs should be adequately irrigated. A layer of organic mulch will help conserve soil moisture and maintain tree health. Several treatment options are available to aid in management including the release of beneficial insects that feed on harmful pests.