Spider mites can be a problem on many different plants, both indoors and outdoors. But at times it seems like they have a special preference for tomatoes. Typically, we first notice we might have a problem with spider mites when we start to see leaves on our plant that have very small, light-colored dots on them, kind of like they might have been sand blasted. This type of damage is usually the result of spider mites.

Spider mites have what we call piercing-sucking mouth parts. Most of us are familiar with aphids and aphids have the same type of mouth. These mouth parts are used to pierce the leaf of a plant and then suck the juices out. Aphids are insects, but spider mites, as spiders, are members of the arachnid family.

One major difference between these two is that aphids are easy to see on your plant while spider mites are very small and thus difficult to see. To confirm the presence of spider mites on your plant, you can actually hold a white piece of paper below a branch and if you shake the branch a bit, you should start seeing tiny black specks on the paper as the spider mites drop off. Another sign, outside of the damage they do, is webbing. If you are seeing webbing on your plants associated with these speckled leaves, you likely have a sizable spider mite infestation.

The damage they are doing to the leaves, reduces the leaf’s ability to provide food to the plant through photosynthesis. These leaves eventually turn brown and drop to the ground and if enough leaves do this, your plant will die.

Spider mites thrive in hot, dry conditions and dry, stressed plants are great targets for spider mites. So, since we can’t control the weather, your first line of defense against spider mites will be to keep your plants watered well.

Spider mites can also build up when we overuse pesticides. The overuse of pesticides will diminish the entire insect population, including those insects that might help defend your plants against these spider mites.

One way to deal with spider mites on your plants is to give the plant a good spraying with a high-powered stream of water. Since not all plants will tolerate this, we have a couple of organic pesticides that work well. One of these is insecticidal soap.

Insecticidal soap is exactly what it says it is soap (potassium salts of fatty acids) mixed with water. Now there are a lot of recipes on the internet for making your own insecticidal soap using dish detergent, but soap and dish detergent are two different things. Will dish detergent work? Yes. Is there a possibility you can harm your plant with dish detergent? Also yes. If you want to make your own rather than purchase pre-made insecticidal soap, at least use one of those pure soaps that are typically sold in health food stores rather than dish detergent. But legit, insecticidal soap is not that expensive.

Neem oil also works well on spider mites, but spraying oils on plants in the height of summer is not a great idea. If you choose to use neem oil, just be sure to try it on a small area of the plant first to see how the oil and an Oklahoma summer get along.

Whether you choose to use water, insecticidal soap, or neem oil, you’re going to need to give the plant a good drenching - being sure to spray under the leaves since this is where spider mites love to hang out. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org