When the weather turns hot and dry, spider mites can generally be found feasting on both ornamental and agronomic plants. Spider mites are eight-legged animals that are more closely related to spiders than they are to insects. The most common spider mite encountered on flowering plants and soybean in Ohio is the two-spotted spider mite. This mite gets its name from two brown spots located on its back. Another common mite found in our landscapes is the spruce spider mite on spruce trees.

In general, spider mites are small and are not easily seen with the naked eye. Therefore, the symptoms of spider mite injury often lead to proper diagnosis. Spider mites pierce the underside of plant leaves and suck out the contents. This leaves behind tiny, pale colored marks that may cover entire leaves. Leaves often take on a brown or bronze appearance, eventually yellow and fall off the plant. Another tell-tale sign of spider mites is a fine webbing linking leaves, flowers, and stems. The webbing often has dust-like particles which are the tiny spider mites.

Spider mite infestations can explode under hot, dry summer conditions when plants are drought stressed. This can make control challenging. The first recommendation for controlling spider mites on outdoor ornamental plants is to water the plants. While doing so, spray the foliage with a heavy stream of water from a garden hose, when possible. Make sure to direct the spray to the underside of leaves where spider mites are present. This will knock off adult mites and can be done frequently. This alone often helps to solve light infestations.

More severe spider mite cases may require additional methods of control. The use of broad spectrum insecticides has been shown to actually INCREASE spider mite populations, likely because insects that help to control mites are also killed. An example of this is carbaryl, the active ingredient in the product Sevin as well as many others.

Safer insecticides that can be used to control spider mites include insecticidal soaps, oils and extracts, as well as spinosid. Here is a little information on each of these:

· Insecticidal soaps. Soaps work when they come into direct contact with the mites. Therefore, coverage of the underside of leaves is essential.

· Spinosid. Spinosid is a natural product derived from soil bacteria. This offers good control of spider mites while being safe for most beneficial insects. It can be found in many insecticide products available at hardware stores and garden centers.

· If you have repeated issues with spider mites on shrubs or perennials, dormant oils can be used during the wintertime when leaves are not present. These oils will smother any spider mites that have overwintered on the bark or in the surrounding soil.

· Horticultural oils and extracts like neem can also be used but may burn foliage when temperatures are high (usually above 90F) and sunlight is intense.

Hopefully these few tips will help you control spider mites this summer. For additional information, please contact the Putnam County Extension office at 419-523-6294, at scheckelhoff.11@osu.edu, or stop in at 1206 East Second Street in Ottawa. You can also find us on Facebook by searching for OSU Extension Putnam County.