6 Signs Your Houseplant Is Infested With Deadly Pests
"Plants are living things. Test infestation is totally normal and treatable," says Erin Marino, plant expert and director of marketing at plant company The Sill. "Common plant pests include mealybugs, scale, spider mites, fungus gnats, thrips, and slugs. These pests might sound creepy crawly, but it’s important to remember these bugs are only interested in your plants—not you, your pets, or your furniture."
An infestation of pests can be tricky to diagnose, says Nick Cutsumpas, the plant coach and urban farmer behind Farmer Nick, because symptoms—yellow leaves, dropping leaves, and discoloration—are similar to those caused by other plant problems such as overwatering. "That said, each pest leaves a specific calling card that is unique to them," he says. "For example, spider mites spin thin webs at the base and underside of the leaf, while scale bugs attach themselves to stems and leave a sticky residue."
Cutsumpas notes that daily check-ins with your plant can help you identify these signs and, ideally, catch them early. "If you wait until your plant suddenly starts dropping leaves, it may be too late," he says.
Once a plant has been infested, you'll want to isolate it from the rest of your plant family immediately. "I treat it for at least a month before assessing whether it has a chance at recovering, and oftentimes I will prune back growth that is beyond saving," Cutsumpas says. "If I find that still doesn't help, I will take cuttings to propagate and send the rest of the plant to the compost pile."
For general treatment, both Marino and Cutsumpas recommend using neem oil ($11), a naturally occurring pesticide that's safe for people, plants, and "good" bugs like bees, butterflies, and ladybugs. "For nearly all houseplant pests, cleaning the leaves and spraying the infested areas with a solution of neem oil, water and a splash of dish soap is an effective method," says Cutsumpas. "This should be repeated at least once a week until the invaders have been defeated, but it is not always a guarantee."
Other helpful remedies for pests like fungus gnats include hydrogen peroxide, repotting with fresh soil, mosquito bits, and yellow sticky traps, says Cutsumpas. "Remember, you're not just battling the pests you can see flying around you; you're also battling the eggs and larvae that lay inside the soil," he notes.
The best defense, Cutsumpas adds, is a good offense. "Proactively cleaning your plant's leaves and making sure your plant is healthy is a preventative method for keeping pests away in the first place," he says. "Pests tend to target unhealthy plants, so the stronger your plant family is, the less susceptible they will be to an attack."
Not sure what's going on with you plants? Below, find specific intel into how to diagnose and treat six common plant pest infestations.
How to deal with common houseplant pests
"If you notice an oval-shaped insect covered by waxy, white cotton-like filaments within your plant, it is most likely a mealybug. They can be found in different parts of the plant but are commonly found on stem nodes, leaf axles, and along the veins on the underside of the leaves—but you may also find them in the root system of the plants," says Marino.
She recommends spot-treating visible bugs with a cotton swab or cotton pad dipped in alcohol, then spraying all of the foliage down with a neem oil solution or insecticidal soap. "Examine your plants weekly for traces of reinfestation," she says.
"Scale are another oval-shaped pest that are enclosed in a shell-like covering if they have matured enough," says Marino. "They are typically brown in color but can also be black or white." These pests are mostly found along leaf veins or on stems.
A mature scale, says Marino, will need to be manually picked off your plant because insecticidal treatments won't penetrate the bug's shell. "After you remove all scale, the plant can then be sprayed down with a neem oil solution or insecticidal soap," she says.
3. Spider Mites
Spider mites are microscopic insects that are usually red or yellow in color. "However, you can easily identify them by the silky webbing they leave behind and grayish stippling on the foliage," says Marino." They usually congregate on new growth on plants and the underside of leaves."
Because they thrive in hot, dry air, you can try boosting the humidity in your home to help ward off a spider mite attack. If that doesn't work, Marino says to use an insecticide that lists spider mites on the label. "Treat your plant after three days, and again in 10 days," she suggests.
4. Fungus gnats
"If small bugs are flying around your plant, they’re probably fungus gnats," says Marino. "Fungus gnats are one-eighth of an inch, grayish, adult flies with delicate wings and long legs. They are often found around the growing season, during favorable conditions, flying around the soil. Fungus gnat larvae, however, feed on organic matter within the soil."
She recommends starting to remove these pests by setting up yellow sticky-traps, which can help capture the flying, adult gnats. "Incorporating diatomaceous earth or mosquito bits in the soil and repotting your plant in fresh soil can help eradicate larvae," she says. "Fungus gnats also love moisture, so let your potting soil dry out completely between waterings."
If you notice elongated insects varying in length from one to two millimeters with a brown or black bodies and bristle-like wings, you likely have thrips in your plants, says Marino. "Younger stages of thrips will appear more light in color to green," she explains."These pests have piercing mouthparts that feed off of cell guts, and the injured plant tissue will have a silvery, stippling appearance. It looks like the chlorophyll is getting scraped off of the plant. New plant growth can come up distorted and brown, and dying tissue may also occur in the areas. Heavily infested plants will have little black dots, which is the pests’ fecal matter."
If you suspect your plant's been infested with thrips, Marino recommends keeping it away from your other plants to avoid spread. Then, use an insecticide spray (like the aforementioned neem oil solution) to fight off the pests.
"You might think of slugs as an outdoor pest, but they can affect houseplants, too," says Marino. "Slugs are nocturnal feeders that can vary in color from gray to brown, leaving slimy trails behind. While these are not as common as other houseplant pests, they may appear from time-to-time."
If ragged holes are developing on leaves, you may have a slug invasion. "They hide under planters and in the soil during the day and can be found directly on the foliage at night, when they come out of hiding," says Marino. "You can try leaching the soil if they are dwelling there at night. Otherwise, I recommend looking into slug pellets and traps if an infestation arises."
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