Common Houseplant Pests
Identifying, treating, and preventing the most frequent pest problems you'll encounter in a houseplant collection.
Mealybugs
Appearance: Small, oval insects covered in a white powdery wax. They cluster in leaf axils, along stems, and at the base of leaves.
Damage: Sap-sucking causes stunted growth, yellowing, and wilting. They excrete sticky honeydew which encourages sooty mould.
Treatment: Isolate immediately. Dab individual bugs with a cotton swab dipped in rubbing alcohol. For larger infestations, spray with diluted neem oil or insecticidal soap weekly until no new activity appears.
Prevention: Regular inspection — especially of new acquisitions. Avoid overwatering, which stresses plants and lowers their resistance.
Spider Mites
Appearance: Barely visible to the naked eye, often reddish-brown or pale. Fine webbing on leaves and stems is the most reliable sign.
Damage: Stippled, yellowed, or bronzed leaves. In severe infestations, leaves drop and plants decline rapidly.
Treatment: Spider mites hate humidity — regular misting and raising ambient moisture helps. Wipe leaves with a damp cloth to remove them. Use neem oil or a miticide spray for heavier infestations. Rotate treatments: mites develop resistance.
Prevention: Avoid hot, dry conditions. Keep humidity up, especially in winter when heating dries the air.
Fungus Gnats
Appearance: Small, dark, mosquito-like flies hovering around soil. The larvae — small, white, transparent — live in the top few centimetres of compost.
Damage: Adults are mostly a nuisance. Larvae damage roots, particularly on seedlings. Signs include sudden wilting and unexplained decline.
Treatment: Let the top layer of compost dry out completely between waterings — larvae need moisture to survive. Yellow sticky traps catch adults. For larvae: water with diluted neem oil, or apply a Bacillus thuringiensis var. israelensis (BTi) drench.
Prevention: Never allow plants to sit in standing water. Use well-draining compost. Top-dressing with coarse grit or perlite deters egg-laying.
Scale Insects
Appearance: Brown or tan, limpet-like bumps attached to stems and the undersides of leaves. Easy to mistake for part of the plant.
Damage: Like mealybugs, they feed on sap and excrete honeydew. Can severely weaken plants if left unchecked.
Treatment: Scrape off manually with a soft toothbrush or cotton swab. Rubbing alcohol kills on contact. Neem oil is effective as a follow-up spray. Scale is stubborn — persistence over several weeks is essential.
Prevention: Inspect new plants thoroughly before introducing them to your collection. Scale spreads readily between nearby plants.
Thrips
Appearance: Tiny, slender, fast-moving insects, usually pale yellow or dark brown. Look for silver streaking or fine stippling on leaf surfaces.
Damage: Rasp the surface of leaves, causing silvery scarring, distorted growth, and leaf drop. Also vector for certain plant viruses.
Treatment: Neem oil, insecticidal soap, or spinosad-based sprays. Thrips have a soil-dwelling pupal stage, so treat the compost as well. Multiple rounds of treatment are almost always needed.
Prevention: Yellow or blue sticky traps are useful for early detection. Quarantine new plants — thrips travel easily and hide well in furled leaves.