Fighting Spider Mites

Spider mites are tiny sucking insects related to spiders and ticks. Depending on the species and season, they can be red, orange, yellow or green. They are difficult to see with the naked eye, but their presence can be detected by the damage they cause. Spider mites can infest many kinds of garden plants and trees and they can be a major pest of houseplants. Outdoors, most species are most active during the warmest months. They may attack indoor plants in any season.

Above: Spider mites, damage and webbing on an indoor gardenia. Top: Leaves dmaged by spider mites, showing pale flecks.

Spider mites feed by chewing on leaves and sucking out the plant’s sap. This action leaves small, pale spots. Plants eventually develop a bronze or grayish cast and/or a scorched appearance, and they may drop their leaves. Spider mites produce webs, but it can be difficult to use webbing as a diagnosis tool because it is easy to confuse with the webbing of true spiders.

Spider mites have several natural predators, including other kinds of mites, dark lady beetles, thrips and big-eyed bugs. Unfortunately their natural predators are often killed by insecticides such as carbaryl (Sevin). Their predators also dislike the conditions that spider mites relish: hot, dry weather.

The best defense against spider mites is to disrupt their favored conditions. Where spider mites have been a problem, keep plants watered during dry spells. Spray plants with a steady jet of water to remove any active spider mites; the force will likely also kill them. Spraying water on the plants also removes the dust that stands in the way of spider-mite predators. If you find webbing where spider mites are suspected and you determine it does not belong to a true spider, destroy the webbing to deter reproduction. Indoors, remove damaged leaves, sealing them in bags before throwing them out. Throw away heavily infested plants. Keep houseplants adequately watered and take measures to increase humidity, especially in winter, by misting the air around the plant and standing the plant on a tray of damp gravel. Periodically wipe the leaves with a damp cloth to remove dust and possible spider mites.

Petri dish image attribution: Forest & Kim Starr

Gardenia image source

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8 thoughts on “Fighting Spider Mites

  1. Spider Mites: just plain awful and very little organic options are available.
    Nothing has ever worked for me until last year I pretty quickly spotted (so to speak) mites in my greenhouse.
    I bought predator mites and they did the job well!

    The trick with spider mites and all disease or infestations is to
    keep your eye on your plants and catch it early. Then perhaps the manual removal and insecticidal sprays can do the job.

    As for Neem oil, it is a preventative and will do NOTHING to stop the progression of bugs or disease. In my opinion.

  2. I have used systemics for spider mites and also dunking the the houseplants in soapy water. I wrap tinfoil around the stem and tighten it over the pot so the soil doesn’t wash away. It must be repeated, often daily but it seems to work on some plants.

  3. I found that none of these techniques worked. I sprayed with water twice to three times a day for a week, used insecticidal soap, acephate and moved my brugmasia to the bathtub to create a damp environment. I finally became frustrated when, after doing all of these things, I saw not one but two sets of webs on the plant in the bathroom. I saw the second set after I manually destroyed the first set as a last resort. It happened over and over again. Of course all the leaves dropped – for the 3rd time. I have never found neem useful for anything. I have conquered squirrels, rabbits, voles and chipmunks, all organically. I wonder if the people who recommend these things have really tried them, or whether they just google a website and copy the answer. My solution was to throw the plant away.

    • Sadly, Brugmansia is another way of spelling spider mite. I know of no organic way to control a badly infested plant. Compost is the only thing.

    • hey
      I usually dont respond on blogs, but your sit seems so similar what happened to me.
      I found (after I had to destroy a whole crop)that a 1% solution of hydrogen peroxide with a drop of rubbing alcohol will kill the critters on contact, repeat every third day for newly hatched. In about 3 weeks you will have no more infestation. One side effect: the leaves sometimes turn brown and/or curl from the alc. But new leaves soon will form when the mites are gone, then cut off all the brown leaves. Oh, and no need to cover the soil, the solution is actually liked by the plants as it kills bad bacteria in the soil.

  4. if humidity and water will kill mites; how about a stand type, hose mounted mister which could be placed over the affected plant and turned on during the day?

    • Hi, Don — yes, insecticidal soap is something to try, but it has been found to be only 40 to 50% effective against spider mites. Most extension agencies recommend cultural control (keeping plants watered, increasing humidity, hosing them down weekly in the sink or shower, wiping the leaves with a damp cloth, etc) as the best method.
      In addition to insecticidal soap, another chemical control recommended for spider mites is petroleum-based horticultural oils or Neem oil, though these also have less effect than cultural controls. With soaps or oils, remember that they should not be applied to drought-stressed plants or while temperatures are above 90˚F (coincidentally, the conditions that spider mites favor!). Read the label closely and follow all directions and precautions.
      Thanks for chiming in!

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