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Here are the most common pests and what to do about them

If you’ve added to your houseplant collection in the last few years, you may occasionally encounter a new plant parenting challenge. What’s the weird cottony thing on my plant? What’s that sticky stuff? These are likely signs of pests, which, if caught early, typically can be controlled. If a houseplant starts to look stunted or scraggly, take a closer look for bugs.

Most often, these pests come from newly purchased plants or from plants that you placed outdoors for the summer. “When you get a new plant or bring one in from the outdoors, inspect it thoroughly,” says Barbara H. Smith, consumer horticulture agent with the Clemson University Home & Garden Information Center. “Look in all the crevices, cracks, and on the underside of leaves to make sure you don’t see anything unusual. Give the plant a little shake and see if anything flies off, too.”

If you find bugs or anything looks suspicious, give the plant a preventive spray with insecticidal soap or neem oil, then let dry before bringing indoors. But make sure to read the label before use because not all products are safe on all types of plants, says Smith. Also, keep pets and kids away from the treated plant. For new plants, even if they look clean, isolate them from other plants in your home for a few weeks before introducing them to the rest of your collection, says Smith. That way, if plants have any hitchhikers, they won’t spread to your other plants.

And one final word of wisdom, which, admittedly, may be tough for some plant parents to hear: If you’ve made several attempts to control bugs and things aren’t getting better (or the plant is severely damaged so that it won’t ever look good again), toss the plant, says Smith. Sometimes you have to sacrifice one ailing plant so you don’t lose others. And, after all, shouldn’t your plants bring you joy, not frustration?

Here are the most common houseplant bugs and what to do about them:

These annoying little gnats are about 1/8-inch long. Fungus gnats fly around or hang out on the surface of the soil in houseplants. While they don’t feed on the plants, they’re extremely bothersome when they flit around you. The good news is they’re really just a nuisance and won’t harm plants, says Smith.

What to do: The larvae feed on organic material such as peat moss, so apply a product containing Bacillus thuringiensis var. Israelensis (BTi) on top of the soil of houseplants, says Smith. This naturally-occurring bacteria disrupt the digestive system of the larvae. Also, avoid overwatering plants or allowing them to stay wet because dry conditions help kill the larvae. While some people like to use yellow sticky traps to monitor for fungus gnat activity, that doesn’t eliminate the source of the problem.

Aphids are soft-bodied pear-shaped bugs that may be green, pink, brown, black or yellow. Some have a waxy coat, and adults may have wings. The 1/16th-inch long bugs usually are found on new leaves or the underside of leaves, says Smith. You also may see honeydew, a sticky material on leaves, which aphids excrete as they suck the plant’s sap.

What to do: Put your plant in the sink or shower and give it a spray to knock down the aphids. (Note: Don’t do this with plants that have velvety leaves, such as African violets, because the leaves will be damaged). Or use a cotton swab dipped in alcohol to rub away the insects. For a heavy infestation, take outdoors and spray with insecticidal soap or neem oil. No matter what technique you use, repeat several times to ensure control, and keep an eye on things for a few weeks.

As you probably guessed, these little critters are related to spiders. Spider mites are about the size of a period on the page, so you may not see them until the plant appears damaged or you spot sticky, silky webs on leaves. Both the babies and adults suck sap, so they will kill the plant in time.

What to do: Spray the plant in the shower or sink, or take plant outside to spray with insecticidal soap. Repeat the treatment once a week for several weeks. Spider mites are notoriously difficult to control, says Smith. If you have a severe infestation, save yourself some frustration and toss the plant.

Whiteflies look like little cotton tufts or tiny moths that fly up when the plant is disturbed, says Smith. Both the adults and babies suck plant sap, with damage similar to that of aphids. They also leave sticky honeydew on plant surfaces.

What to do: Spray the plant in the shower or sink, and take outside to spray with insecticidal soap, especially lower leaf surfaces. Repeat the process in a few days or so, but heavily infested plants may need tossed.

Scales vary in appearance and color. They may look like a waxy blob or fish scale you can scrape off with your fingernail. The adults are not mobile, but the babies do crawl and feed on plant sap. Scales usually are found on stems and under leaves.

What to do: Early infestations can be removed by scraping off with your fingernail; if you’re too grossed out by that, you can use something like a nail file or toothpick. The adults are protected by their waxy coating, so neem oil can be used to smother them. The babies can be controlled with insecticidal soap.

Mealybugs are whitish 1/8- to ¼-long insects that move very slowly on plants. The adults are covered with a white waxy cottony-looking substance. The immature bugs, called nymphs, look similar but smaller. These usually are found on the lower surface of leaves or where leaves attach to the stem, says Smith. They also excrete honeydew.

What to do: Wipe off individual bugs with a cotton swab dipped in rubbing alcohol. Or use an insecticidal soap. For bad infestations, you’re probably better off tossing the plant.