By Bailey Walten 1991 Newsletter
Mites, ranging in size from minuscule to microscopic, are among the most serious pests to the landscape. Mites are Arachnids, not insects, and are closely related to spiders, having eight legs and mouthparts adapted for sucking. The category of mites we are most concerned with are the spider mites. They feed on a wide variety of plants such as spruce, hemlock, pine, fir, arborvitae, holly, privet, boxwood, rhododendron, azalea, oak, maple, sycamore, linden, and honey locust; to name a few. Each spider mite feeds by using a pair of needle-like stylets (teeth), called chelicerae, that tear open the plant cells. The mouth is then inserted to suck up the sap as the chelicerae probe deeper to rupture more cell membranes. This feeding results in tiny speckles or stippling of the leaves. When populations are high, the entire leaf surface can turn tan or yellow leaving a chlorotic appearance to the plant. The foliage dries out and later drops as a consequence. Like spiders, many species of spider mite have the ability to produce silk and will spin layers of webbing over the vegetation where they are feeding.
In small populations, these mites pose little threat to our plants.Several predators such as ladybird beetles, certain thrips, and a few varieties of predacious mites can help to control them when numbers are low. Unfortunately spider mites begin feeding and breeding before their predators appear and due to their incredible pro-creational propensity, can cause severe damage by virtue of sheer numbers in a short period of time. It’s not unusual to find hundreds, even thousands, of egg shells and cast nymphal skins on a single leaf.
A simple way to test for mites is to vigorously shake a branch over a piece of clean white paper. If tiny specks are seen scurrying across the page, you have mites. Alberta spruce, blue spruce, boxwoods and hemlocks are the most routinely attacked plants that we have observed over the years. An effective miticide such as Kelthane is needed to bring them under control.Two to three applications starting in late Spring and continued throughout the Summer are usually necessary. If an Indian summer persists, a Fall treatment may be indicated. Repeated use of broad spectrum insecticides such as Sevin can actually exacerbate the problem by killing the predators but not the mites. So for example, a miticide should be added to the spray mix when Sevin is being used on a spruce to control bagworms; especially when multiple applications are required.
Mites are extremely common; not only in the landscape, but in the ears of our pets (ear mites), in our bed linens (dust mites), even in us (follicle mites). Because they are so tiny and generally innocuous, we are normally unaware of their presence and we coexist very naturally. In the event that they become a problem or nuisance, good sanitation and if necessary, timely miticide applications can be made to safely and effectively bring their numbers back within tolerable limits.