Finding insects on a plant you care about is unsettling. The good news is that most houseplant pests can be managed without strong chemicals, as long as you know what you are dealing with.
Identification comes first. Clemson HGIC points out that a single pesticide will not kill every kind of pest, and some only work on certain life stages. UC IPM adds that most houseplant decline comes from care problems, so confirm you have pests before you treat. Below is how to tell the common ones apart, then a treatment ladder that starts with the least toxic options.
Before you treat: isolate and inspect
- Move the plant away from others. UC IPM says to isolate it immediately and wash your hands after handling it.
- Use a 10× hand lens. Clemson recommends one for small pests and immature stages. Check leaf undersides, leaf joints, stems and the soil surface.
- Look for honeydew. Penn State notes that you may see clear, sticky honeydew before you see the insects. Aphids, whiteflies, mealybugs and soft scale all produce it, and sooty mould grows on it.
Pest identification table
| Pest | What you see | Where to look | Source |
|---|---|---|---|
| Spider mites | Tiny light speckles (stippling) on leaves; later yellowing or bronzing; fine webbing in heavy infestations | Leaf undersides; adults about 0.5 mm (0.02 in) | UC IPM, Colorado State |
| Mealybugs | White, cottony or waxy insects; sticky honeydew | Leaf veins, leaf axils, tight crevices; some species on roots | UC IPM, Clemson |
| Scale | Small brown or grey, mostly immobile bumps; soft scales leave honeydew | Stems and leaf undersides; can look like spore clusters on ferns | UC IPM, Clemson |
| Aphids | Small, soft, pear-shaped insects; white cast skins; curled or distorted new leaves | New growth and leaf undersides | UC IPM, Clemson |
| Thrips | Slender insects under 3 mm (1/8 in); silvery or speckled leaves with tiny black dots | Leaf undersides, flowers, crevices | UC IPM, Colorado State |
| Whiteflies | Tiny white winged insects that flutter up when disturbed; scale-like immobile young | Leaf undersides | UC IPM, Clemson |
| Fungus gnats | Small dark flies running over the potting mix; larvae with shiny black heads in the mix | Soil surface, windows, lights | UC IPM, Clemson |
Two tiny mites need a microscope. UC IPM says broad mites and cyclamen mites are recognised by thickened, brittle, stunted new growth rather than by sight. See our cyclamen mite guide.
The treatment ladder, least toxic first
1. Remove what you can by hand
Clemson says early infestations can often be handpicked, and scale may need scraping off with a fingernail. Prune and bag heavily infested shoots (UC IPM). Colorado State notes that a light disturbance of a settled scale can break its mouthparts.
2. Wash the plant
UC IPM says soft-bodied insects and mites can often be removed with water. Spray sturdy plants with water, covering every surface. Clemson says repeated water sprays help control spider mites. Colorado State calls a vigorous jet of water particularly effective for spider mites and aphids.
3. Spot-treat with rubbing alcohol
For small mealybug infestations, UC IPM suggests dabbing 70% (or weaker) isopropyl alcohol on the insects with a cotton swab. Test it on a small part of the plant one to two days beforehand. Colorado State warns that alcohol can burn leaves, so keep it on the insect. Alcohol is flammable and is not a registered pesticide.
4. Use sticky cards for flying adults
Yellow sticky traps catch whiteflies, winged aphids and fungus gnats (Colorado State). UC IPM says they can sometimes reduce whitefly and fungus gnat numbers. They will not solve a problem alone, because the young stages stay on the plant or in the mix.
5. Insecticidal soap or horticultural oil
If washing is not enough, UC IPM recommends a soap or horticultural oil labeled for your plant and pest before other insecticides. Clemson says insecticidal soap is most effective on aphids, mealybugs, scale crawlers, thrips, whiteflies and spider mites. It only works on contact and has no effect once dry, so coverage matters and repeat sprays are often needed.
Oils include petroleum-based horticultural oils and plant oils such as neem (UC IPM). Colorado State calls horticultural oils the most effective spray for spider mites and scales. For more, see our neem oil guide and neem oil vs insecticidal soap comparison.
6. Target fungus gnat larvae in the mix
Let the mix dry between waterings (Clemson, UC IPM). Products containing Bacillus thuringiensis subspecies israelensis (Bti) treat larvae in the potting mix (UC IPM). See our fungus gnat guide.
7. Other labeled insecticides, last
UC IPM says to use other pesticides only when other methods have failed, and to avoid broad-spectrum, long-residual products. Systemic soil-applied products are an option for some soft scales and aphids. UC IPM’s list of less toxic insecticides warns that systemic neonicotinoids such as imidacloprid can be very toxic to bees and parasitic wasps. The RHS does not support pesticide use and recommends non-chemical and biological controls.
Treatment by pest
| Pest | Start with | If a product is needed | What makes it hard |
|---|---|---|---|
| Spider mites | Repeated water sprays; reduce dust (UC IPM) | Horticultural oil or soap labeled for the plant (UC IPM, Colorado State) | Fast life cycle; Colorado State calls soaps only marginally effective |
| Mealybugs | Alcohol swab, washing, pruning (UC IPM) | Soap, oil or neem oil on young nymphs (UC IPM) | Wax repels sprays; root mealybugs are missed (Colorado State) |
| Scale | Scrape off; wash crawlers away (UC IPM) | Oil or soap, best on crawlers (UC IPM) | Adults are protected by their covering (Clemson) |
| Aphids | Water spray; prune (UC IPM) | Soap or oil labeled for the plant (UC IPM) | Kills only aphids present on the day (UC IPM aphids) |
| Thrips | Rinse leaves (Clemson) | Soap or oil on exposed stages (Colorado State) | Eggs sit inside tissue; later stages develop in soil (Colorado State) |
| Whiteflies | Wash; yellow sticky traps (UC IPM) | Repeated soap or oil sprays (UC IPM) | Only sprayed insects die; cover leaf undersides |
| Fungus gnats | Let the mix dry; empty saucers (Clemson) | Bti drench (UC IPM, Clemson) | Larvae in the mix, not on leaves |
Spray safely
- Read the label. UC IPM says to use a product labeled for indoor use on your plant species and the pest you identified. Clemson notes labels list sensitive plants.
- Cover leaf undersides thoroughly (UC IPM, Penn State).
- Do not spray stressed plants. UC IPM’s spider mite guidance says not to use soaps or oils on water-stressed plants or above 32 °C (90 °F).
- Watch for injury. Clemson lists distorted leaves, yellowing, spotting and burned edges, often visible within 5 to 10 days.
- Spray outdoors if you can, in mild weather, and bring the plant in once dry (UC IPM, Clemson).
When to stop
UC IPM says control of an established houseplant pest is sometimes impractical, and that discarding the plant and starting fresh may be best. Colorado State says seriously infested plants are often best discarded because they can infest others. If the roots are infested, Clemson suggests rooting a cutting in a clean pot of sterile mix.
Plant-specific pest guides
Spider mites on houseplants, pothos spider mites, parlor palm spider mites, pothos mealybugs, string of pearls mealybugs, pothos scale, pothos thrips, hoya whiteflies, croton pests and sticky honeydew on indoor citrus.
References
- UC Statewide IPM Program: Pest Notes: Houseplant Problems
- UC Statewide IPM Program: Less Toxic Insecticides
- UC Statewide IPM Program: Pest Notes: Mealybugs
- UC Statewide IPM Program: Pest Notes: Spider Mites
- UC Statewide IPM Program: Pest Notes: Aphids
- Clemson Cooperative Extension HGIC 2252: Common Houseplant Insects & Related Pests
- Colorado State University Extension: Managing Houseplant Pests
- Penn State Extension: Pest and Disease Problems of Indoor Plants
- University of Maryland Extension: Diagnose Indoor Plant Problems
- Royal Horticultural Society: How to help a poorly houseplant