There aren’t too many pests that get to be troublesome on our houseplants, at least compared to our outdoor gardens, but of those you might see, spider mites are one of the worst. It’s startling how quickly these pests can spread as they suck the life out of our houseplants’ leaves.
One of the qualities that makes spider mites so insidious is that they’re super easy to spread. They can hitch a ride on new plants you bring in, cutting a fresh bouquet from the garden, sneak in an open window, or even on your clothes if you’ve been in a garden center or other area with an infestation.
Another issue that comes with these arachnids (technically spider mites aren’t insects—they’re more closely related to ticks and spiders) is that they can reproduce really fast—in just a week in the right conditions. This means populations can build up quickly and go from a light infestation to an outright outbreak in short order.
Two-spotted spider mite adults and eggs. Photograph by CSIRO, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
Identifying Spider Mites
Spider mites feed by jabbing their needle-like mouthparts into plant cells (something like mosquitoes), so the first thing to watch for is stippling on the leaves as they suck plant cells dry.
The next most common sign is webbing. Like their name suggests, spider mites create a fine webbing (like cobwebs). You’ll most commonly see this on the underside of plant leaves, but if infestations get severe enough, they may encase the new growth, stunting and killing the plant’s tender young shoots in a mass of webs.
Treating Spider Mites
Because they reproduce so quickly, you’ll want to start treating as soon as you see stippling. This is especially important if the infestation is still in early stages so that the population hasn’t built up enough to produce a lot of visible webbing. Start by washing off the plant leaves in your sink, shower, or outdoors with a hose. The more of them you dislodge, the less you have to treat for. Tip: For smooth-leafed plants, wiping the top and bottom of the leaf with a wet paper towel can remove even more.
Let the leaves dry, then treat your plant with a horticultural oil or miticide. While you might be tempted to look for an insecticide, resist the urge. Since they’re not technically insects, many common insecticides won’t be as effective on them. Tip: Because the pests reproduce so quickly, you’ll want to treat on a weekly basis for at least three or four weeks to get any babies that hatch from eggs after you treated.
If you want to go natural, consider beneficial (predatory) mites. These tiny creatures do the work for you, hunting and killing spider mites until they reduce the population to nothing. Beneficial mites don’t harm your plants, but they do take a while to become effective, especially if your houseplant(s) have a high mite population when you start. On the plus side, you only need to release them once—like mites, they reproduce and you’ll have generations of hungry mite killers as long as there are spider mites around.
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By Dan Heims, president of Terra Nova Nurseries
Photographs courtesy of Terra Nova Nurseries
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