Two-Spotted Spider Mite
The two-spotted spider mite, Tetranychus urticae, a pest of apple, peach, and other fruit trees, also feeds on a wide range of both wild and cultivated plants. These insect-like organisms are tiny (1/20 inch) and are difficult to see without a magnifying glass. Despite their small size, their populations build to high numbers very rapidly on the leaves of fruit trees, causing the leaves to yellow.
Fully grown females and some immature males overwinter under bark scales on tree trunks or among fallen leaves and in other protected places on the ground. With the arrival of warm weather in the spring, these mites leave their places of hibernation and start wandering about looking for food plants. Almost all of those on tree trunks crawl down to the ground, where they feed on weeds and grasses.
The first eggs usually can be found around the first week in May. In warm weather, they hatch in 5 to 8 days. A complete generation from egg to adult might require no more than 3 weeks. From five to nine generations hatch in the orchard each season, depending on the weather. In mid- or late summer, when drought and other factors such as weed removal cause poor food conditions among weeds and grasses, mites move from the old host up tree trunks or to low-hanging apple branches in contact with ground vegetation. Low-hanging branches that touch grass or weeds usually are attacked first; then the mites spread upward and into the tree's interior.
Once established, the population can become a serious infestation and might cause injury. Injury to leaves resembles that caused by the European red mite, except that a grayish cast is more prevalent. These mites also spin a fine silken web over many infested leaves. In the fall, the adults either remain in the tree or leave it and hibernate among weeds, leaves, or in the soil.
Two-spotted spider mites should be monitored and managed in much the same way as European red mites.