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Plantgasm - I love plants too much. By Derek Powazek.

Attack of the Spider Mites

Ever noticed tiny silk webs on the leaves of your indoor plants? You may have just assumed they were spider webs, but they may not be. They may be the webs of spider mites.

The difference is important because spiders (order Araneae) are generally good for your plants – they don’t hurt the plants and eat things that do. But spider mites (order Acari) are bad for your plants. They feed on the plant, sucking the life out. And if their webs get out of control, they can encapsulate plant entirely. Kinda impressive for bugs smaller than the period at the end of this sentence.

I’ve got a lot of tropical plants in the house, which are particularly susceptible to spider mites. My lovely wife shot some video of them with a great magnifying lens. Warning: this video will make your skin crawl. Watch it fullscreen for maximum creepiness.

How to know if you’ve got ’em: Tiny webs and yellowing leaves. Sometimes you can see them in bright light – they’re tiny, but quick.

What to do: Spider mites generally aren’t a chuck-the-plant kind of problem, but they are damaging and require vigilance. Here are a few things I’ve used to keep them in check.

  1. Hands. When you’re tending your garden, if you notice the webs, just reach out and wipe them away to keep them from getting established. Don’t worry, spider mites can’t hurt you, but use a paper towel you can toss or a cloth you can wash so that you don’t inadvertently spread them to other plants.
  2. Sprays. Most pesticides don’t work very well on spider mites. Some are so harsh they can hurt the leaves, which kind of defeats the point. Worse, some insecticides can make a spider mite infestation worse, because they can kill off predatory insects.

    If you’re going to spray, go for a horticultural oil spray or use Neem if you can stand the smell (I can’t). I’ve had some luck using sprays that contain Pyrethrum, which is a poison derived from Chrysanthemums. Be sure to test any spray on one plant before using it on all of them, just in case there’s a bad reaction. And generally it’s better to spray at night when it’s cool and the leaves are out of direct sunlight.

  3. Predators. I just tried this for the first time last week. The idea is, introduce another mite that eats spider mites, but does not spin webs or eat plants. Seems like a good idea. Unfortunately, I can’t say that it worked. I’ve been looking at the leaves under magnification all week and see no sign of the “good” mites. Maybe I just got a bad batch. I may try again. Either way, this is really only a solution if you have a ton of plants like me. It’s not worth it for a couple of houseplants.

The best thing you can do is make your environment inhospitable. Spider mites like hot, dry air, so mist your plants with plain old water frequently. The misting also makes the webbing easier to see – so wipe it off when you see it. And if you have a plant with a particularly bad outbreak, isolate it so it doesn’t spread.

Sorry for any nightmares that video causes.

Gardeners: Have you found any techniques to be particularly effective against spider mites? Please share.

See Also

9 Responses

I had decent luck with a pyrethrum spray. I wouldn’t use it inside around my cats, since pyrethroids are very toxic to cats. Outside, however, they deteriorate under UV light. Pyrethrin is the natural derivative of chrysanthemums, and it deteriorates within a couple of days, whereas some of the synthetic pyrethroids last significantly longer.

Something I’ve seen a lot of people recommend but which didn’t work for me at all was spraying with neem oil. All that did was make my plants smell slightly citrusy and slightly rotting-peanutbuttery.

Posted by Owen on 17 August 2011 @ 6am

Impressive video!

There’s no magic bullet for mites; I find I have best results when I try more of a death-by-a-thousand-cuts approach.

I water in the shower, with a detachable showerhead, and spray the tops and bottoms of the foliage at the same time. It isn’t a cure for mites, but it’s somewhat emotionally satisfying to think that I’m inconveniencing them, and I think it does help keep small problems from turning into large ones. Misting the plant with soapy water and then spraying with a showerhead set to “massage” seems to work better, when there’s a definite infestation happening.

Moving mite-afflicted plants out of direct sun helps too, when possible.

I am pleased to see someone else describe the smell of neem as having peanut-buttery qualities. (I’d been wondering if maybe it was just me.) Neem does work, but requires multiple applications a few days apart, and of course you have to treat all the plants, not just the one with the problem, if you want any kind of permanent relief.

The option that’s done the most to reduce mite-related aggravation for me, though, is to just stop growing plants that consistently develop bad mite problems. I’ve stopped growing crotons, English ivy, (reluctantly) ti plants, and Dracaena thalioides, and I don’t even attempt Brugmansia/Datura or Alocasia/Colocasia.

Posted by mr_subjunctive on 17 August 2011 @ 7am

Insecticidal soap worked for me. I used the “Safer” brand but you can find formulas to make your own. I use it on potted bamboos, and everything that I keep indoors under lights all winter. Recently I had to spray some Colocasia that were infested, and it worked great there too.

Posted by Alan @ it's not work, it's gardening! on 17 August 2011 @ 7am

Most of my pest control is the by-hands-squishing-method… Have you ever tried lady bugs? I hear that they eat all sorts of plant pests – and they’re fun to have around. I might try getting a batch for my greenhouse this winter as an experiment.

Posted by Zach on 17 August 2011 @ 9am

Ugh, I hate those things … We always have a problem with spider mites, and I’m battling them on my office plants right now. Creepy little punks.

Posted by Jess on 17 August 2011 @ 5pm

I find insecticidal soap will kill adults but you need keep to keep spraying every few days in hot weather. Avid works great and has a residual effect but of course it’s a poison, but I’m not dead yet! Works on cyclamen mites too.

Posted by Ed Kramer on 18 August 2011 @ 6am

I use insecticidal soap (Safer) with rubbing alcohol – about a shot glass to each cup of solution. I keep a spray bottle full, and spray when I see them. If it’s bad or the plant is big, it gets sprayed in the shower, and rinsed off after. I only have indoor plants, though. I think stressed plants – pests- or otherwise – are just more susceptible, so my goal is just stay on top of them, and keep my plants happy. And if a plant turns out to be a high maintenance diva that needs conditions I can’t provide, or it’s a bug magnet, it usually goes. It’s hard to like a sad ugly plant.

Cool video btw. I didn’t know they moved so fast. Curious what all those little specks are in the webbing. If it’s what I think, you can add really bad housekeeping to their other faults.

Posted by Thomas on 22 August 2011 @ 8pm

I only made it through a couple of seconds of that video! Yuk!

I use a mix of rubbing alcohol and water, with a few drops of dish soap. It seems to work well on spider mites and mealy bugs, especially if you catch the infestation early. The alcohol fries the pests and the soap helps the alcohol stay on the leaves. I’ll treat infected plants about once a week for a few weeks until I’m confident they’re gone. If the infestation is advanced (which I’ve only seen once or twice in my work), the plant gets tossed rather than risk other plants in the area.

I also do what mr_s does and avoid plants that are prone to mites.

Posted by Liza (Good To Grow) on 22 August 2011 @ 9pm

I feel relieved that I’m not the only one that feels I’m constantly battling these creepy crawlies! thanks for all the tips!

Posted by ellieT on 26 August 2011 @ 10am


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