What are spider mites?

Spider mites are often thought of as insects, but they are not. They have eight legs instead of six, thus they are more closely related to spiders than insects. There is typically three life stages to spider mite: eggs, immatures that look like adults but are smaller and adults. There several types of spider mites, but here we will only address boxwood two-spotted spider mites.

The boxwood spider mite is about the size of a period and is yellow-tan. Their eggs overwinter on leaves and twigs. They prefer English boxwoods and sometimes American, but rarely Japanese ones.

The boxwood spider mite feeding causes a yellow stippling of leaves. In heavy infestations, entire leaves may turn mostly yellowish-white, and leaves may prematurely drop.

In the winter, look at the bottom of leaves showing stippling from the previous season for yellow eggs. In spring and early summer, look on the leaf top and bottom of new growth for yellowish mites. One way to monitor is to place a white sheet of paper under some branches and then beat on it a few times. Pull the paper out and allow any debris to fall off the paper due to gravity, then swipe your hand across the paper. If any smears appear, then you most likely have mites and the boxwoods should be treated. Their monitoring process is called “the beat test”.

The two-spotted spider mites are bigger than the boxwood spider mites. They are bigger than a period or about 1/2 mm long. They are greenish-yellow with a black spot on each side of the body in the growing season. The eggs are white to yellow. They are known to attack annual and perennial flowers, many deciduous shrubs and some trees. One of their favorite shrubs is the burning bush euonymus.

Spider mites suck the leaf juices, causing white-to-yellow stipples to appear. When there are large infestations, the stippling may turn the leaves white to yellow to grayish brown and die.

The two-spotted spider mite likes the weather hot and humid. They often start on the inside of a plant that is dense from many years of shearing. Examine the plant for stippling and any signs of mites on the bottom of the leaves. Also, use “the beat test” to determine if spider mites are present. Webbing may appear, but may not be as visible as real spider webs usually are.

How are spider mites controlled? We here at Virginia Green use a dormant oil in late fall and winter to control overwintering stages of this pest. During the rest of the year, we use a miticide and/or a summer oil to control the active stages. These sprays help to control the spider mites and are less harmful to benefit such as lady beetles and phytoseiid mites.

If you have boxwoods, burning bush euonymus and other plants you suspect have mite problems, allow us here at Virginia Green to help you monitor and care for them.