Mealybugs are soft, sap-sucking insects that hide in a protective white waxy coating — often looking like little tufts of cotton wool tucked into a plant. They’re a very common houseplant and greenhouse pest, they multiply steadily, and their waxy coat makes them stubborn to clear. This is a general guide; adapt the response to your specific plant.
Identification
- Cottony / waxy appearance: small (a few millimetres) oval insects covered in white powdery or cottony wax; clusters look like specks of cotton wool.
- Slow-moving; often sitting still in colonies.
- White waxy egg sacs alongside the adults.
Where they hide
- Stems, nodes and leaf axils (where leaf meets stem), and along leaf veins/undersides.
- Tucked into tight, sheltered spots — new growth, flower buds, under leaf bases.
- Roots / root mealybugs — some species live on roots in the soil, appearing as white waxy deposits in the root ball; suspect these when a plant declines with no pest visible above soil.
Damage & commonly affected plants
Mealybugs drain sap, weakening the plant, stunting and distorting growth, and causing yellowing or leaf drop in heavy infestations. They affect a very wide range of plants — especially houseplants, succulents, cacti, citrus, orchids and many ornamentals.
Honeydew & sooty mould
Like aphids and scale, mealybugs excrete sticky honeydew, which coats leaves and surfaces and grows black sooty mould. Sticky leaves or black film are often the first clue before you spot the insects themselves.
Ants
Ants farm mealybugs for their honeydew and protect them from predators, so persistent ant activity on a plant can signal (and sustain) a mealybug problem — controlling ants helps natural predators do their job.
Isolation
Isolate an affected plant immediately — mealybugs crawl to neighbouring plants, and a small colony spreads through a collection surprisingly fast.
Manual removal
- For light infestations, dab individual mealybugs with a cotton bud dipped in rubbing alcohol, or wipe/pick them off.
- Rinse or wash the plant to dislodge colonies; check hiding spots thoroughly afterward.
- Prune out heavily infested shoots.
Cultural controls
- Inspect regularly (they hide, so look into axils and undersides).
- Don’t over-fertilise with nitrogen — soft lush growth favours them.
- Keep ants off the plant.
- Quarantine new plants before adding them to a collection.
Treatment principles
- Start least-toxic: alcohol spot-treatment, thorough washing, and low-toxicity products such as insecticidal soap or horticultural/neem oils, applied to reach the hidden colonies — the waxy coat repels water, so thorough coverage matters.
- Biological controls (e.g. mealybug-destroyer beetles, parasitic wasps) work well in greenhouses/indoors.
- No single product suits every plant — use one labelled for your plant and follow the label exactly; never exceed labelled rates. For suspected root mealybugs, treatment differs (drenching/repotting) — check guidance for that specifically.
Repeat inspection
The waxy coat protects eggs and adults, so one treatment rarely finishes them. Re-treat and re-inspect at intervals over several weeks, checking every hiding spot, until no new mealybugs appear.
Prevention
- Quarantine and inspect new plants (the usual way mealybugs arrive).
- Check vulnerable plants (succulents, citrus, orchids, soft-stemmed houseplants) routinely.
- Control ants; avoid excess nitrogen; wipe dust and keep plants healthy.
Common mistakes
- Missing hidden colonies in axils, on undersides or on roots.
- Treating once and stopping (eggs survive).
- Ignoring ants that keep re-seeding the infestation.
- Poor coverage — the wax repels light spraying.
Quick questions
What are the white cottony bits on my plant? Almost certainly mealybugs (or their egg sacs) — check stems, leaf axils and undersides.
Why do they keep coming back? Hidden colonies, surviving eggs, or ants farming them — repeat treatment, reach every hiding spot, and control ants.
My plant declines but I see no pest — could it still be mealybugs? Possibly root mealybugs in the soil; inspect the root ball for white waxy deposits.
Related guides
- All plant pests & protection
- Spider mites · aphids · powdery mildew
- Thrips on plants · why plants flower but don’t fruit
- Choosing a plant sprayer for applying treatments · all plant pests & protection
