My tomato plant’s leaves are turning brown, and I am seeing some webs. What’s going on? SP

Your description and the presence of webbing suggests you have a problem with spider mites.

One of the problems with identifying spider mites on your plants is that the insects are so small they are difficult to see with the naked eye (isn’t “naked eye” an odd phrase?). The presence of webbing is a key indicator.

If you would like further confirmation, you can hold a sheet of white paper under some of the leaves while shaking the branch a bit. After doing this, if you see some tiny dark specks, you will have confirmed the presence of spider mites.

True to their name, spider mites are in the arachnid family which makes them related to spiders, scorpions, ticks, and daddy-long-legs. The presence of webbing tells you that you have a large infestation on your plants.

One of the challenges associated with spider mites is their rapid life cycle. After mating, female spider mites can generate a dozen eggs every day for a couple of weeks with this new generation of spider mites reaching maturity with a week. With this ability to reproduce quickly, you can see how an unchecked population of spider mites can get overwhelming pretty quickly.

Another way to identify spider mites is by the damage they do to the plant. Spider mites have what are called piercing-sucking mouth parts. Feeding occurs when they poke that little sucker into the leaf and remove the liquid from the leaf. This type of damage reduces the plant’s ability to produce food for the plant via photosynthesis. Leaves with spider mite damage have small little specks all over them. Eventually they will turn brown and fall off. After enough leaves fall off, the plant will die.

And guess what… spider mites love dry, hot weather! Have we had any of that recently? Plants that are stressed by dry, hot weather have changes in their chemistry which makes them more attractive to spider mites.

Jen Dominiak-Olson, of the OSU Extension Plant Pathology Lab says that “the number one tomato problem in the summer without a doubt is spider mites.” So, based on the weather conditions favorable to spider mites, a lot of you should be seeing them.

One of the best things you can do to help defend your plants against spider mites is to keep them hydrated. Right now, in Oklahoma, that is almost a full time job. If you are starting to see signs of spider mite damage on your plants, you can use water to hose down the plants, which will remove the spider mites from your plant. This is a good first line of defense.

Overuse of pesticides in your garden can also contribute to a spider mite infestation. When we use pesticides such as carbaryl (Sevin) we are very effectively killing off all the insects, even those who would love to dine on our spider mites. These insects would include lady beetles and predatory thrips. For this and many other reasons we encourage minimal use of pesticides. And when using pesticides, it’s best to use organic pesticides which are at the lower end of the toxicity scale and have a shorter pre-harvest interval (the time between your use of a pesticide and when you can safely harvest your produce).

There are several organic pesticides that can be effective against spider mites including insecticidal soap, neem oil, and horticultural oil. Follow the directions on you chosen product and be sure to apply early in the morning or evening to avoid the presence of pollinator insects.

Every time I bring up insecticidal soap, I feel the need to get up on my soapbox. Reason being, that there are a variety of recipes posted on social media and the internet with recipes for making your own insecticidal soap. At first glance, this seems like a very economical solution. But dish detergent is typically not soap. Dish detergents contain a variety of chemicals such as de-greasers, coloring, sudsing agents, etc. and these chemicals can damage your plants.

Insecticidal soap typically has two ingredients: water and soap (aka potassium salts of fatty acids). You will be hard pressed to find potassium salts of fatty acids in your dish detergents.

When pesticides are used properly, there shouldn’t be a lot of collateral damage to other insects in your garden. For insecticidal soap to work, you will need to apply it directly onto the spider mites. You will essentially need to soak your plant from top to bottom because spider mites like to hide under the leaves.

Neem oil and horticultural oil are usually good solutions as well but, in this heat, covering your plants with oil can cause them to overheat, damaging your plants. So, do a test spraying if you plan to use one of these to reduce potential damage.

Spider mites can also become a problem on house plants. Not only can you take these plants outside to give them a spray with the hose, but insecticidal soap and horticultural oils are appropriate for indoor use. See you in the garden.

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: O.P. Sharma, Bugwood.org