This heat is tough on not only us, but also our plants. At this point in the season, it’s a challenge to provide enough water for them to survive, let alone thrive. It can also be a challenge to muster up the desire to get out in the heat and do all those garden tasks we know need to be done. As a result, everything seems to suffer in this heat. However, there’s one garden pest that seems to thrive in times like these and they are spider mites.

Spider mites can become an issue with indoor plants, but right now they should be coming into their own in our gardens. Spider mites make their home on a variety of plants, but they do seem to have a special preference for tomatoes.

You will likely first notice a problem with spider mites when you begin to see lightly colored dots on the leaves of your plants, kind of like they were sand blasted. When you see this starting to appear, the culprit is likely spider mites.

The lightly colored dots are the result of spider mites feeding on your plants. Spider mites have what are called piercing-sucking mouth parts. They use these parts to penetrate the leaf of the plant and suck out the liquid inside. With enough of this type of damage on the leaf, your plant loses its ability to photosynthesize, and the plant eventually dies. In larger infestations, you will also likely see some degree of webbing on your plant.

Spider mites are members of the arachnid family and are difficult to see with the naked eye due to their size. If you want further confirmation of the presence of spider mites above and beyond the associated damage, you can hold a white sheet of paper under some leaves and shake the leaves. When you do this, you should begin to see tiny, black dots begun to appear on the paper. These dots are the spider mites.

I say we should be seeing a rise in the presence of spider mites because they thrive in hot, dry conditions. These conditions tend to stress plants, and stressed plants are the preferred targets of spider mites. So, your first line of defense is to keep your plants watered well.

Spider mites can also become a problem when we overuse pesticides in our garden. Overuse of pesticides tends to not only reduce the presence of pest insects but also the other insects that might help defend you plants against a spider mite infestation. So as always, keep your use of pesticides to an absolute minimum and also try to use organic pesticides. 

Fortunately, we have some pretty simple ways to deal with spider mites. First of all, like mentioned earlier, keep your plants hydrated. Secondly, you can hose down your plants with as strong of a stream of water that they can stand. This will wash off the spider mites and likely drown a few. Using insecticidal soap is another good strategy.

Neem oil will also work well on spider mites, however using neem oil during the height of summer heat can be problematic outdoors. The reason for this is that it being an oil, the oil can cause the plant to retain heat by limiting its ability to cool down. Plants cool down via small openings in the leaves called stomata that open and close to control gas exchange and water regulation. The oils can clog these up and with the summer heat, this can be devastating. So, it’s best to avoid using horticultural oil in the heat of summer.

When using insecticidal soap to treat for spider mites, you’ll need to soak the plants, being sure to get the underside of the leaves also. You need to do this because the underside of leaves is where the spider mites like to live. 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: Frank Peairs, Colorado State University, Bugwood.org