Houseplant pests are exasperating and can be difficult to eradicate. It seems as if pests can swarm your plant in a matter of seconds. One day, your plant is green and healthy, but the next, aphids have taken it over, and its leaves are sticky with honeydew.
Fear not: There are solutions to your insect pest dilemma. Read on to find out the top 10 houseplant pests, then learn the top 11 ways to eradicate them from your plants.
- The Top 10 Houseplant Pests
- Scale Insects
- Aphids (Greenflies)
- One Mite That’s a Real Pain – Spider Mites
- Soil-Dwelling Surprise Guests
- Fungus Gnats
- Millipedes and Centipedes
- Slugs and Snails
- Top 11 Control Methods for Houseplant Pests
- Check Your Plants Often
- Quarantine New Plants
- Quarantine Infested Houseplants
- Spray With Rubbing Alcohol
- Spray Neem Oil
- Wash the Plant
- Add Systemic Insecticide
- Squish Insects
- Use Yellow Sticky Traps
- Vacuum Flying Insects
- Cut Off Infested Plant Parts
- More Information on Common Houseplant Pests
The Top 10 Houseplant Pests
… But First, a Word from the Hemiptera Order
We’ll start with a group of insect pests from the Hemiptera order, which consists of related insects that everybody loves to hate!
You’ve never heard of this order? No worries – you’ll definitely recognize the insects that belong to it.
- Shield bugs
- Jumping plant lice
And many more!
Hemiptera insects have piercing-sucking mouthparts. That is, their mouth is a straw that pierces the leaf surface, injects saliva and enzymes to break down the leaf innards, then sucks up the liquified plant goo. Large numbers of these insects injecting enzymes will make the plant unhappy. (Note: This is also how bedbugs work, only on humans. Ugh!)
Because these insects are in the same order, they share the same lifecycle and the same control methods. What works on one insect in this order will also work on the rest.
Read on about scale insects, mealybugs, whiteflies, and aphids, and remember that these are all cousins.
The adult insect looks like fish scales on plants – hence the name.
Scale insects are common on outdoor plants as well as houseplants. When they hatch, the nymphs are almost microscopic and move around. This is when scale insects are most vulnerable to control measures – and when they’re least likely to be noticed.
When scale nymphs become larvae, they attach themselves to the plant and start feeding. They pupate and become an adult covered with a waxy shell, and they never move from that spot again.
Some scale shells look like small brown or tan bumps, while some resemble tiny upside-down dinner plates stuck to the back of a leaf. Scales can infest any part of a plant, including flowers.
As they feed, scale insects (like most other pests from the Hemiptera order) will excrete honeydew, a sugary substance that brings in ants to farm and protect them.
The sugar leads to sooty mold, a gray fungus that spreads across the leaf. Plants infected by scale or any of their cousins will look nasty.
On outdoor plants, crawlers come out to play in spring. Indoors, they run amok in all seasons. Once the scales have matured and developed their waxy shell, they’re mostly immune to contact insecticides.
The waxy shell also protects the baby crawlers because scale insects keep their babies between their belly and the leaf. Even if you kill off the insect, its babies are still growing and developing under the shell! So squishing or scraping off the shells is an important part of controlling them. Spraying rubbing alcohol is also effective.
Mealybugs are pink, white, or grey insects, generally covered with what looks like bits of waxy cotton. (Note: Some whitefly species living on the leaf will also sport the bits of waxy cotton.) This fluffy material protects them from moisture loss and heat. These retain their legs all their life and move freely around the plant.
Most mealybugs live on the leaves, but a few will take up residence on the roots, leading to yellow leaves, wilting, stunted leaves, and a few blossoms. They can be found on any place on the plant, but often squeeze themselves into tight spaces like leaf whorls where they can’t be squished or sprayed with pesticides.
Mealybugs can be a hard insect to eradicate once they make their home on your houseplants, but a little effort and the use of several control measures at once usually do the trick.
Wash infected plants with soap and water. Spray the plant with the sink hose to wash bugs and crawlers off the leaves. Wipe mealybugs with a swab dipped in rubbing alcohol. They can be sprayed with alcohol if the plant is able to tolerate it – more below. But always squish the mealybugs along with the other control methods. Squishing and handpicking are methods they cannot develop immunity to.
If you bump your houseplant and a cloud of tiny, white insects fly up like snowflakes, your plant has whiteflies. This is the annoying adult stage of these insects, but they don’t damage your plants the way the non-flying whiteflies do.
Like its Hemipteran cousins, whitefly nymphs and larvae will cluster on the undersides of leaves, tuck in against the veins and against the stem, leave sticky honeydew, and damage the plant in large numbers. Though they’re more of a nuisance than a threat, large numbers of them can stunt your houseplants and make them drop their leaves.
Plant leaves will look stippled or sometimes be wrinkled and distorted. White specks and translucent yellow spots will populate the bottoms of the leaves. The translucent spots are whitefly nymphs, aka crawlers.
Whiteflies go through complete metamorphosis, and they’ll have all four life stages going on simultaneously – egg, nymphs (or crawlers), larvae, and adults.
The crawlers move from place to place, drinking all the plant sap. When they’ve matured – after about one week – they’ll molt and then attach themselves to the stem with their proboscis, drinking sap until they become a pupa. The adult emerges from the pupa and flies around and starts laying eggs.
A full life cycle, from egg to adult, takes about 18 days! So, any control measures will need to be repeated every 5 to 7 days for several months. Never use one chemical control for whiteflies (or any other insect), but switch them out to keep the insects from developing immunity to them.
Aphids are one of the most common pest insects, both outdoors and indoors. They are soft-bodied, tiny bugs in green, black, red, or brown. Like its Hemiptera cousins, it drinks sap out of the leaves, produces sticky honeydew, reproduces like a house afire, and can go from a newly hatched (or newly born) aphid to an adult in 10 to 14 days.
Fun fact: Females can lay eggs AND give birth to live aphids. What’s more, aphid females can produce viable eggs without the assistance of a male!
Adult aphids can spit out three to five babies per day until they die or get killed, usually within a month of their birth.
However, control measures still work.
One way to control aphids is by blasting them with a stream of water to knock them off the plant, with the shower or the spray hose in the sink. Insecticidal soaps, neem oils, and rubbing alcohol (on certain plants) are also good control measures.
Here endeth the list o’ insects from the Hemiptera order.
One Mite That’s a Real Pain – Spider Mites
Spider mites are common houseplant pests. They’re not insects – they’re a type of arachnid, more closely related to spiders, ticks, and scorpions. These near-microscopic mites make leaves look mottled or pale from sucking out plant juices. They can be red, yellow, brown, or green, depending on what type of spider mite it is.
Look on the back of the leaf to find tiny spider webs and what appears to be fine salt-and-pepper grit. The grit and tiny webs are classic signs of spider mites.
Spider mites love dry conditions and low humidity (though this doesn’t stop them from taking over large shrubs outdoors in August when the relative humidity is 95%).
Putting plants in the sink or shower and spraying them with water will discourage spider mites – more so if you can get underneath the leaves and rub away the webbing and dust that protects these creatures. Lost webbing can also force them to stop laying eggs until they can spin new webs.
Spider mites can be particularly frustrating on houseplants. Mites don’t play by the same rules that insects do, so insecticides don’t bother them.
Follow these steps to fight spider mites.
- All susceptible houseplants must be treated for spider mites at the same time.
- Get rid of badly infested plants.
- Cut back plants with heavy infestations.
- Cut off leaves and stalks with populations of spider mites.
- Wash plants and rub away all webbing. Let them dry.
- Spray plants with neem oil or horticultural oil to smother mites.
- OR spray the plant with 70% isopropyl alcohol (rubbing alcohol).
Repeat these steps at one or two-week intervals until the spider mites have been completely killed off for several weeks.
Soil-Dwelling Surprise Guests
These insects require different control methods, as many of these live part or all of their lives in the plant’s soil.
The tiny gnat flying around your houseplants is likely a fungus gnat, but this annoying fly is not the real pest here. The adult gnats have non-functioning mouthparts, so they can’t bite or feed. It’s the fungus gnat larvae dwelling in your houseplants’ soil that is the problem.
Fungus gnat larvae live in the top 2 or 3 inches of potting soil, eating decaying plant matter, fungi, and algae. However, they also eat plant roots as well as the unrooted ends of cuttings. Back when I was a horticulturist, I’d check the geraniums I was trying to root, only to find tiny fungus gnat larvae, like tiny white worms, gnawing on the base of the cuttings.
Soil insects are a little tougher to kill off, especially with the adults flying from plant to plant and laying eggs in each pot.
Here’s how to control fungus gnats:
- First, place sticky yellow traps right at the soil level to catch fungus gnats as they emerge, as well as around the houseplants. These will help take care of the adults.
- Second, let the top 2 inches of soil dry out in your houseplants. Fungus gnat larvae need moist conditions to thrive, and this will make them miserable. Good!
- Third, get some Bacillus thuringiensis israelensis(BTI) soil drench. Now, this is not generally available in retail – but mosquito dunks are. Find dunks that contain BT or BTI, a microbial insecticide that targets flies. This includes mosquitoes … and fungus gnats.
- Fourth, put a dunk in your watering can. Keep it filled with water for a few months, and use this watering can to water your plants. The BT is a living microbe that will take up residence in your soil more and more as you water.
This is a slower means of control, but they will kill off the fungus gnat larvae and keep living in your soil, so they can’t come back for a good while.
Also called roly-polys, sowbugs, woodlice, or armadillo bugs, pillbugs are isopods, a type of crustacean that lives on land. Fun fact: Pillbugs are more closely related to shrimp and crawdads than to insects, so they need moisture to stay alive – in dry conditions, they can survive only a few days.
Pillbugs are scavengers, eating mainly decaying plant material and organic litter, but sometimes, they’ll eat young seedlings or vegetables touching the ground.
They’re helpful because they break organic material down into soil. But they can be a nuisance when they hitchhike indoors on a houseplant that has been outdoors all summer. As cute as pillbugs can be, nobody wants to see an army of pillbugs marching out of a flowerpot in the kitchen window.
The best way to deal with pillbugs is by completely repotting the plant. Dump the pillbug-infested soil outdoors in the compost, rinse off the plant roots, and pot it in fresh soil in a new pot (or an older one that’s been scrubbed in soap and water). Do this to any other plants with pillbugs.
Keep them separate from any pots that still have old soil in them for three weeks to be sure the pillbugs are no longer infesting any of your pots.
In the meantime, clean up your plant area so there are no damp corners or old soil-encrusted flowerpots for pillbugs to hide out.
Millipedes and Centipedes
These long arthropods with many feet are quick. Though some are said to be poisonous, this isn’t a huge concern. Only the largest species can bite through the skin, and they bite only when they’re being picked up or crushed.
These also can pop out of flowerpots that have been brought in from outdoors. Follow the control measures above used for pillbugs.
If they are a real problem in other parts of the home, seal cracks where they might come indoors and sprinkle diatomaceous earth (DE) around these areas. Don’t breathe in the dust.
Slugs and Snails
Slugs don’t have a shell; snails do; both go around sliming everything (and eating holes through your leaves). These generally hitchhike in from plants brought indoors in the fall.
Handpicking is effective, though be sure to look underneath leaves and on stems to catch any snails or slugs in hiding.
Diatomaceous earth (DE) cuts through the protective slime coating and kills them. If you don’t have DE, get some sidewalk chalk like little kids use, scribble all over a piece of wood or cardboard, and set it, chalk side down, on the side of the pot above the soil. I discovered how effective this was when my little daughter had been drawing pictures on the sidewalk, and the next day, I found an exploded slug had attempted to crawl over one of the chalk lines. Not for the faint-hearted.
These were once classified as insects, as I learned in Entomology class a million years ago. These days, they’re categorized as hexapods.
Springtails are named for their spring-loaded “tail” that’s bent under their body. When threatened, the spring “tail” is released, catapulting them into the air and (presumably) out of danger.
These tiny creatures are found in potting soil, eating organic material but sometimes chomping on seedlings and tender plant roots.
A large number of springtails in the potting soil means the plant is being overwatered. Like pillbugs, springtails need moist and humid conditions to survive.
Allowing the soil to dry out between waterings will discourage springtails.
Top 11 Control Methods for Houseplant Pests
There are ways that are almost universal for knocking down harmful houseplant pests. Here are 7 control methods that are super-effective at stopping infestations. However! For best results, use two or three control methods at the same time.
Check Your Plants Often
As Yogi Berra said, “You can observe a lot by just watchin’.”
- Shiny sugar spills
- Discolored or distorted leaves
- White or brown things on your leaves
- Annoying tiny flying insects
- Houseplants that look puny or less healthy for no reason
- Dropping leaves
Any of these signs warrants checking your plants over for insects.
Quarantine New Plants
New arrivals should sit in a well-lighted spot away from the others for at least three weeks. If any pest eggs have hitchhiked in, this will give them time to hatch and start roaming around – and time for you to kill off these pests before your plant joins the others.
Quarantine Infested Houseplants
Insects will move from plant to plant, and an infestation that could have been contained can soon take over your whole houseplant table.
Spray With Rubbing Alcohol
This is very effective against pests, especially if you have a large infestation. The alcohol dries them out, and they utterly perish. The alcohol evaporates quickly after it’s done its damage. You can also dip a cotton swab in rubbing alcohol and touch it to the insect pests, or use a small brush to get it into plant crevices where pests are hiding.
The 70% isopropyl rubbing alcohol can be used at full strength, undiluted. Never use the 90% -- it will burn your plant!
Alcohol can be sprayed weekly. Spray weekly for about a month until the pests are killed and their eggs hatch, and the young pests are also wiped out.
A plant with infested roots and leaves can be dipped in rubbing alcohol. Take the plant out of the pot, rinse the soil off the roots, then dip the whole plant, roots and all, into the alcohol. Then, repot in clean soil and keep it out of the sun for a day or two. Don’t use it on the soil.
When using rubbing alcohol, remember these tips.
- FIRST, spray a small area of the plant to make sure the leaves don’t burn. Some plants, like ferns, delicate tropicals, and waxy-leaved plants, are sensitive to rubbing alcohol.
- SECOND, keep the plant away from direct sun and in the shade for a day or two. Plants with alcohol on them will burn.
- THIRD, spraying flying insects with rubbing alcohol doesn’t work – though it does feel therapeutic. Use sticky trap cards to catch them instead.
- FOURTH, use rubbing alcohol only on indoor plants. This is a harsh solvent. Large amounts of it used indiscriminately will kill off the helpful elements of your soil as well as helpful insects.
- FINALLY, don’t mix rubbing alcohol with any other substance when you’re spraying.
Spray Neem Oil
This is an organic way to control both diseases and insects. An oil spray will clog the insects’ breathing holes, suffocating them. It’s also systemic, so it is absorbed into the plant and does its work from the inside.
Add 1 teaspoon per gallon of water, and add two or three drops of mild dish soap to help it stick to the plant. Spray neem oil on all surfaces, on top and bottom of leaves and on the stems, because this works best if it gets on the insects. The oil needs to coat the insects to kill them. Neem oil also gets rid of the unsightly, sooty mold that comes with honeydew-emitting insects.
Stick faithfully to a monthly spray schedule of neem oil for best results and to nip any problems in the bud.
Wash the Plant
Washing the houseplant with a bit of soap added to the water will kill off insects. Those that aren’t killed are more vulnerable to other control methods. It makes the plant look better, too.
Add Systemic Insecticide
These granules are scratched into the soil and watered in. The systemic insecticide is absorbed by the plant, making the sap poisonous to the insects.
Houseplant pests can develop a resistance to various poisons. But they will never develop resistance to being squished.
Use Yellow Sticky Traps
Yellow sticky traps are great for capturing and killing flying pests such as fungus gnats and whiteflies. Even if you don’t have any flying insects at the moment, these yellow cards are a good way to monitor houseplant pests and catch them when they make an appearance.
Read more: Gnat Problem? Honest Sticky Trap Review!
Vacuum Flying Insects
This might not be a highly effective means of control, but it sure feels good.
Bring a handheld vacuum cleaner over to your plant, turn it on, and shake the plant and suck up insects. Avoid sucking up the plant in the vacuum. Empty the vacuum outside so you don’t re-release your pest insects in the house.
Cut Off Infested Plant Parts
If you have a bad infestation that you can’t seem to get under control, cut your plant back by a third or even by a half. This will get a lot of insects out of the house and will give you a smaller area to concentrate on when applying control measures.
Pro Tip: Never rely on a single method of control. Use several different control measures at the same time. Houseplant pests will build up resistance to different chemicals, but using several means of control can knock down the pests before they get to that point.
More Information on Common Houseplant Pests
The Fayette County (Kentucky) Extension horticulturist has a helpful video on identifying houseplant pests.