Spider Mites on Italian Cypress Is a Hot Weather Problem

Q. My Italian cypress had spider mites, so I sprayed the trees with an insecticide about six weeks ago. Nearby Italian cypress trees are also full of spider mites. I was going to spray them with an insecticide until I listened to your Desert Horticulture podcast which told me to use a miticide instead. Which one should I use?

This Browning could be from spider mites, watering too often, or borers. If it occurs in the middle of summer it's very likely spider mites.

A. Spider mites are a hot weather insect so spraying when it's not summer just for them doesn’t make much sense. However, spraying oils in Fall and Winter months makes perfect sense for insects that might spend the winter on your trees.

Horticultural oils, sometimes called dormant oil or spray oil, is the best insurance to prevent insect outbreaks like aphids, spider mites, and scale insects.

            Remember, spraying insecticides make mite problems more likely on susceptible plants like Italian cypress. Miticides, unlike insecticides, are less likely to cause mite problems later. Spider mites are nearly always present on all plants they feed on. There are lots of insects that feed on spider mites as well and keep them in check.

Spider mites, like their name suggests, usually leave a webbing that you can see when there is damage.

            These predatory insects hunt down spider mites and use them for food. Think coyotes and rabbits. Spraying traditional insecticides like Malathion, Sevin and even organic insecticides like Neem oil or soap and water kills most insects off, good ones as well as the bad one you wanted to control. The primary benefit of organic sprays are its environmental safety and short life after its sprayed.

When spider mites are active they can create a bluish green cast when they are actively feeding and often times then leaves of Italian Cypress are "dusty". Spider mite damage always starts in the heat of the summer.

            If an insecticide must be sprayed for some reason, watch the sprayed plants very carefully during hot weather to see if spider mites become a problem or not. Frequently spider mites will become a problem after spraying an insecticide because their predators were killed. I realize sometimes you must, but spray insecticides as a last resort.

Close-up of the needles or foliage of Italian Cypress and spider mite damage.

            Miticides are chosen because spider mites are more like spiders than insects and sprays that kill insects oftentimes don’t kill spider mites. I am glad you did not use an insecticide for mite control. It would have made the problem worse and probably not killed the spider mites.

            Use the University of California Integrated Pest Management websites (“Google” them by using your favorite search engine and typing in “UCIPM” and “spider mites”). Read these notes. They are written by entomologists who specialize in controlling pests. After reading these notes you will be better informed than 90% of the landscapers spraying plants.

            The UCIPM notes will recommend spraying oils like canola, clove and cinnamon oils as well as horticultural oils and sulfur sprays to control spider mites. In our hot desert environment these sprays may damage plants during the hot months. It is cool enough in the Fall, Winter and Spring you can spray oils without damaging most plants. Plants that may be damaged will be listed on the label.