Fungus gnats
What they look like: tiny black flies, roughly 1/8 inch long, hovering around the soil or flying up when you disturb the plant. They look like very small fruit flies but stay near the soil rather than near food.
The damage: the adult gnats are mostly just annoying. The larvae, which live in the top few inches of moist soil, can damage young roots and seedlings. Established plants usually tolerate them, but large populations can stress the plant.
What causes them: consistently moist soil, especially with organic material like peat or bark. The larvae need moisture to survive. Overwatered plants are especially prone.
How to get rid of fungus gnats
- Let the soil dry more between waterings. This is the most effective long-term fix. Larvae cannot survive in dry soil. Let the top 2 inches dry out before watering
- Yellow sticky traps placed at soil level catch adults and break the egg-laying cycle
- Hydrogen peroxide drench: mix 1 part 3% hydrogen peroxide with 4 parts water and use it to water the plant. It kills larvae on contact without harming the plant (the fizzing is normal)
- BTi (Bacillus thuringiensis israelensis): sold as Mosquito Bits or Gnatrol. Soak the granules in water overnight and use the water to irrigate. The bacteria kill larvae over 2 to 4 weeks
- Top-dressing with sand or perlite: a half-inch layer of coarse sand or perlite on top of the soil dries quickly and makes it harder for adults to lay eggs
Treat for at least 3 to 4 weeks because the adult life cycle continues after the larvae are killed. Sticky traps break the adult cycle while soil treatments break the larval cycle.
Spider mites
What they look like: nearly invisible to the naked eye. You will see the damage before you see the mites. Look for: fine webbing between leaves or in stem joints, and leaves with a dusty, stippled, or bronzed appearance. Hold a white piece of paper under a branch and tap it; if tiny moving specks fall onto the paper, those are mites.
The damage: mites pierce leaf cells to feed, causing the stippled appearance. Heavy infestations cause leaves to yellow, dry out, and drop. They can kill a plant if untreated.
What causes them: hot, dry conditions. Spider mites thrive in low humidity and warmth. They often appear on plants near heating vents in winter, or on plants moved back indoors from a dry summer.
How to get rid of spider mites
- Increase humidity immediately. Spider mites struggle to reproduce in humid air
- Shower the plant: take it to a sink or shower and spray all leaf surfaces, especially undersides, with a strong stream of water. This physically removes mites and eggs. Repeat every 3 to 4 days
- Neem oil spray: mix neem oil with water and a few drops of dish soap as an emulsifier. Spray all leaf surfaces thoroughly, including undersides. Apply every 5 to 7 days for 3 to 4 weeks
- Insecticidal soap: effective for direct contact. Must thoroughly coat the mites to work
- Isolate the plant immediately from all other plants. Spider mites spread very easily through contact and airflow
Mealybugs
What they look like: white or cream-colored cottony tufts, usually found in the joints where leaves meet stems, along stems, and in any crevice of the plant. They move very slowly. They also produce sticky honeydew, which coats nearby leaves and can develop into a black sooty mold.
The damage: mealybugs suck sap from plant tissue, weakening the plant. Heavy infestations stunt growth, cause leaf yellowing and drop, and can kill a plant over time.
What causes them: they hitchhike in on new plants most often. They are also attracted to stressed or overfertilized plants (high nitrogen levels attract them).
How to get rid of mealybugs
- Isopropyl alcohol on a cotton swab: dab each mealybug directly. The alcohol penetrates the waxy coating and kills them on contact. Effective for small infestations
- Alcohol spray: for larger infestations, mix 1 part 70% isopropyl alcohol with 1 part water in a spray bottle and spray the entire plant, including leaf undersides and stem joints
- Neem oil spray: disrupts the mealybug life cycle and acts as a repellent. Apply every 5 to 7 days
- Repeat for 3 to 4 weeks minimum. Mealybug eggs are protected and may survive the first treatment
- Isolate the plant from all others during treatment
Scale insects
What they look like: small brown, tan, or reddish dome-shaped or flat bumps on stems and the undersides of leaves. They do not move once settled and can easily be mistaken for part of the plant's natural texture. Scrape one off with a fingernail: if a flat protective disc comes away with a soft body inside, it is scale.
The damage: like mealybugs, scale suck sap and secrete honeydew. They can be particularly persistent because the hard protective shell shields them from many treatments.
How to get rid of scale
- Manual removal first: use a soft toothbrush, cotton swab, or your fingernail to scrape scale off stems and leaves. This is tedious but effective for knocking down numbers
- Isopropyl alcohol: after scraping, wipe the stems with a cloth or cotton pad soaked in 70% isopropyl alcohol to kill remaining crawlers (the juvenile mobile stage)
- Neem oil spray: targets crawlers effectively. Apply to all plant surfaces weekly
- Systemic insecticide (imidacloprid soil drench): for severe or persistent infestations on non-edible plants, a systemic insecticide absorbed through the roots kills scale feeding on sap. Follow label instructions carefully
- Repeat treatment for 6 to 8 weeks. Scale is one of the harder pests to fully eliminate
Thrips
What they look like: tiny, slender insects about 1mm long, ranging from pale yellow to dark brown or black. They are fast-moving and often hard to see. The signs are more visible than the insects: leaves develop a silvery, papery, or scarred appearance with small black specks (frass) on the surface.
The damage: thrips feed by piercing cells and sucking out the contents, leaving behind the distinctive silvery scarring. They also spread viruses between plants. New growth is often distorted or stunted in heavily infested plants.
What causes them: they often come in on new plants or can blow in through open windows in summer. They are attracted to flowering plants and new growth.
How to get rid of thrips
- Sticky traps: blue sticky traps are more effective for thrips than yellow ones
- Shower treatment: strong water spray knocks thrips off leaves. Repeat frequently
- Neem oil or insecticidal soap spray: apply to all leaf surfaces. Thrips hide in flower buds and leaf folds, so thorough coverage is essential
- Spinosad: a naturally derived insecticide particularly effective against thrips. Available as a spray or soil drench
- Thrips are persistent. Expect to treat for 4 to 6 weeks
Aphids
What they look like: soft-bodied insects about 1 to 3mm long, ranging from pale green to yellow, black, or brown depending on species. They cluster on new growth, flower buds, and stem tips, often in large numbers. They do not move quickly and are usually easy to spot once you know what to look for.
The damage: aphids suck sap from soft new tissue, causing stunted, distorted, curling new leaves. They produce large amounts of honeydew, leading to sooty mold. Heavy infestations can significantly weaken a plant.
How to get rid of aphids
- Water spray: a strong stream of water knocks aphids off and kills many on contact. Very effective for early infestations. Repeat every 2 to 3 days
- Insecticidal soap or neem oil spray: spray directly onto colonies. Reapply every 5 to 7 days
- Remove heavily infested stems: if a particular shoot is dense with aphids, simply remove it rather than trying to treat it
- Aphids are generally one of the easier pests to eliminate with consistent treatment
Root mealybugs
What they look like: white cottony masses in the soil and around the roots, discovered when you unpot a plant. Unlike regular mealybugs, they are not visible above the soil line, which makes them easy to miss until the plant shows unexplained decline.
Signs of root mealybugs: the plant wilts, yellows, or stops growing despite adequate watering and light. No pests are visible on the leaves. When you remove the plant from its pot, you find white waxy material coating the roots and soil.
How to get rid of root mealybugs
- Remove the plant from its pot and shake off as much soil as possible
- Rinse the roots thoroughly under running water
- Soak the bare roots for 10 minutes in a diluted neem oil solution or insecticidal soap solution
- Repot in fresh, clean potting mix in a clean or sterilized pot
- Treat with a systemic insecticide soil drench after repotting to catch any remaining eggs
- Discard all old soil; do not reuse it
Treatment toolkit
These are the most broadly useful treatments to keep on hand:
Prevention
The most effective pest control is not letting pests establish in the first place. A few habits make an enormous difference:
Quarantine all new plants
Every new plant, regardless of where it came from, should spend at least 2 weeks in a separate room before joining your collection. Inspect it thoroughly during this period. Most pest outbreaks in home collections started with a single new plant.
Inspect regularly
Check leaf undersides and stem joints whenever you water. Early infestations are easy to treat; established ones are not. A monthly thorough inspection (including removing plants from pots to check roots once a year) catches problems before they spread.
Avoid overwatering
Consistently moist soil invites fungus gnats and root rot, which weakens plants and makes them more susceptible to all other pests. Most houseplant problems, pest-related and otherwise, trace back to overwatering.
Good airflow
Stagnant air encourages mold and some pests. A small fan running on low in a room with many plants helps prevent the humid, still conditions certain pests prefer.
Wipe leaves
Dust on leaves blocks light and provides cover for spider mite eggs. Wiping leaves with a damp cloth once a month keeps the plant healthier and removes pests before they establish.
Do not over-fertilize
High nitrogen levels produce soft, lush growth that is particularly attractive to sap-sucking pests like aphids and mealybugs. Fertilize at the recommended rate, not more.
Frequently asked questions
How do I get rid of fungus gnats in houseplants?
Let the soil dry more between waterings — larvae cannot survive in dry soil. Use yellow sticky traps for adults, and treat the soil with a hydrogen peroxide drench (1:4 with water) or BTi (Mosquito Bits solution) for larvae. Treat for 3 to 4 weeks to break the life cycle.
How do I know if my plant has spider mites?
Look for fine webbing between leaves and a dusty, stippled, or bronzed appearance on the leaf surface. Tap a branch over white paper: tiny moving specks are mites. They thrive in hot, dry conditions and spread rapidly, so act immediately.
What do mealybugs look like?
White or cream cottony tufts, usually in leaf joints, along stems, and where leaves meet the stalk. They move very slowly. The white material is a waxy coating. They also produce sticky honeydew that can lead to black sooty mold on nearby leaves.
How do I get rid of mealybugs?
Dab each mealybug with a cotton swab soaked in 70% isopropyl alcohol. For larger infestations, spray the entire plant with a 1:1 alcohol-water mixture. Follow up with neem oil spray every 5 to 7 days for 3 to 4 weeks. Isolate the plant from all others during treatment.
What are the brown bumps on my plant's stems?
Almost certainly scale insects. Scrape one off: if a flat disc comes away with a soft body inside, it is scale. Scrape off what you can, treat with isopropyl alcohol and neem oil spray, and repeat weekly for 6 to 8 weeks. Scale is persistent but treatable.
How do I prevent pests on houseplants?
Quarantine every new plant for 2 weeks before placing it near others. Inspect leaf undersides and stem joints when you water. Avoid overwatering. Keep good airflow around plants. Wipe leaves occasionally to remove dust and pest eggs.
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