Spider Mites

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Spider mites are a common plant pest that cause plant damage by sucking plant juices out of leaves and needles. They cause the plants to have a dull, unhealthy appearance. The most common outdoor spider mite is the two-spotted spider mite. They are less than 1/16^th of an inch in size and are difficult to see with out a magnifying lens. They have eight legs, which makes them different than true insects that have six legs. This makes them closely related to ticks and spiders.

If you have a plant with a dull appearance, you can use a sheet of white paper and do a spider mite test. While holding the white paper under a leaf or branch, tap the leaf or branch and look for specks that may fall on the paper. The specks will look like dust or pepper, only they will move! If there is a large infestation you may notice some fine webbing on the branches. With severe cases the leaves of the plant will become yellow or bronze looking and drop off.

There is several control methods you can try once you determine you have a spider mite problem. Mites tend to attack plants under stress. So keeping the plants watered and fertilized will reduce stress and help prevent the mites from moving in. A forceful spray of water can remove a lot of mites. Be sure to spray the undersides of leaves. This will need to be done on a regular basis to keep populations low. Highly refined oils sold, as superior or horticultural oils are also effective in controlling spider mites. The oil suffocates the mites. These oils are different than dormant oil. They can be applied to foliage without damage by following the directions on the label. There are miticides available to control spider mites. Contact your county Extension office, Master Gardener hotline office or local nursery for more guidelines on spider mite control.

Reference: MU Guide G7274 Aphids, Scales and Mites On Garden and Landscape Plants

Tom Fowler, FowlerT@missouri.edu
Regional Specialist, Agriculture and Horticulture
Buchanan County, MO
University of Missouri Extension