Miticides are used to control mites, which are among the most difficult arthropod pests to control on ornamental plants.
Adult mites have eight legs and piercing/sucking mouthparts that are used to suck fluids from the cells of host plants. The first immature stage of a mite, referred to as the larva, has only six legs, like insects. The exceptions are the Eriophyid mites, which have four legs in all stages. Mites are not insects, but are more closely related to spiders and ticks. Thousands of species of mites feed on plants.
Spider mites, members of the Tetranychidae family, are perhaps the most important mite pests of ornamental plants. The name – spider mites – is due to the many members of this family that produce silk webbing. Spider mites are medium-sized mites that feed on a wide variety of host plants from many different plant families. Some spider mite varieties include bamboo, Lewis, southern red, spruce, tumid, and two-spotted mites.
Mites of a given species can develop very rapidly when temperatures, relative humidities, host plants, and other factors are optimal. In fact, for many mites, the time to develop from an egg to an adult can be less than a week. Generally, mite development occurs more rapidly at higher temperatures, up to a point.
Due to mites’ rapid development, scouting should be performed frequently – at least once per week – and miticide applications may need to be made at weekly intervals or more frequently during the summer. Be sure to check the miticide labels for instructions and restrictions associated with spray intervals.
Frequent, careful inspection of plants is necessary to detect mite infestations before they reach epidemic levels and cause severe plant damage. By the time plant, symptoms become very obvious to the unaided eye, control of the mites will be difficult and potentially expensive. Early detection can limit damage and facilitate economical control of mites.
Careful inspection is necessary because damage due to mites can, on some plants, resemble that from other causes. For example, symptoms can look similar to insect feeding, nutritional deficiencies, physiological stress, herbicide damage, etc.
Since many mites feed on the undersides of leaves, these are important sites to check. Spider mites can usually be detected on older leaves, whereas Tarsonemids are often found on young leaves. False spider mites often feed near the midrib or veins. Silvery speckling/stippling of the upper leaf surface is a characteristic symptom of leaf feeding. You may also notice fine, thread-like webbing if there are spider mites present.
Mites may also feed on petioles, stems, buds and other plant parts. Mite feeding can cause a multitude of symptoms, such as leaf cupping, discoloration, distortion, spotting, speckling and stunting, stem russeting and discoloration, as well as distorted and discolored flowers.
Because mites are so small, the use of a magnifying hand lens (10x) will make it easier to observe them. Another technique frequently used to detect mites, especially on crops with fine foliage like ornamental asparagus, is to slap stems firmly on a light-colored surface, such as a white painter’s palette or a sheet of white paper on a clipboard. If mites are present, they will be easily seen as small, moving spots.