Identification
Insects covered in a white, cottony, waxy coating, gathering in leaf axils, at the base of shoots and on the underside of leaf blades. They look like tufts of cotton wool. They suck sap, weaken the plant and excrete sticky honeydew, on which black sooty mould develops. A common pest of houseplants and succulents. Adult females are oval, soft-bodied insects about 2-5 mm long, with a pinkish or grey body hidden under wax, often bearing waxy filaments along the sides and at the tip of the abdomen. Males are tiny, winged and do not feed. In most species eggs are laid in white, cottony ovisacs (cocoons), from which mobile larvae (crawlers) hatch and spread across the plant, carrying the infestation to neighbouring specimens; some mealybugs (e.g. Pseudococcus longispinus), however, are ovoviviparous and give birth to live crawlers without a distinct ovisac. In the warm, dry conditions of homes and glasshouses mealybugs develop all year round, in several overlapping generations - which is why a single treatment is rarely enough. Feeding symptoms are stunted growth, yellowing, deformation and premature leaf drop, and under heavy infestation dieback of shoots; the black sooty mould on the honeydew further reduces photosynthesis and disfigures the plant. A separate form is the root mealybug (Rhizoecus), forming white, waxy clusters on the roots and inside the root ball - the plant weakens and wilts with no visible pest on the above-ground parts. Mealybugs are often attended by ants, which eat the honeydew and protect the colonies from natural enemies.
Treatment
Spot removal with a stick dipped in alcohol (spirit), washing with potassium soap, and oil-based or systemic preparations in the case of heavy infestation. New plants are best kept in quarantine - mealybugs spread easily from plant to plant. The foundation is early detection and regular inspection of hidden spots - leaf axils, shoot bases, the underside of leaf blades and the space around the pot - because small colonies are far easier to remove mechanically than extensive ones. An infested plant is isolated from the others, and heavily attacked shoots are cut out and removed. Potassium soap and oil emulsions (paraffin or rapeseed oil) dissolve the protective wax layer and block the insects' breathing apparatus, but act only by contact - every mealybug must be thoroughly wetted and the treatments repeated every 7-10 days to cover each successive hatching generation. The waxy coating and hidden sites make contact sprays unreliable; a systemic insecticide is then more effective, taken up by the plant and reaching the insects regardless of the waxy shield. Under cover and in container growing, introducing natural enemies gives good results at low and medium intensity - the predatory ladybird Cryptolaemus montrouzieri and parasitic wasps (Leptomastix). It is also worth controlling the ants that protect the colonies, and in the case of root mealybugs replacing the substrate, cleaning and rinsing the roots or watering the plant with a systemic product. Chemicals are used in rotation and according to the label to reduce the risk of resistance.
How to tell it apart from look-alikes
| Feature | Mealybugs | Scale insects |
|---|---|---|
| Appearance | White, cottony, fluffy tufts of wax; soft body, clearly visible | Flat or convex scales (brown, grey) clinging to the shoot like scabs |
| Mobility | Larvae and adult females move slowly throughout their lives | Immobile once settled; the scale is separate from the insect's body |
| Honeydew and sooty mould | Abundant sticky honeydew, with black sooty mould on it | True armoured scales do not excrete honeydew (unlike soft scales) |
| Waxy coating | Fluffy, cottony, easily rubbed off with a finger | Smooth, hard scale, difficult to scrape off, protecting the insect from spray |
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Mechanical removal and plant isolation | Spot treatment with a stick or cotton bud dipped in alcohol (spirit), washing with a stream of lukewarm water; infested and new plants in quarantine away from the rest. | From the first tufts of cotton wool; at low intensity it may be sufficient. |
| Potassium soap and oil emulsions | Washing with potassium soap or oil (paraffin/rapeseed) dissolves the wax and blocks the breathing apparatus; acts by contact, several treatments needed. | Repeat every 7-10 days, because generations overlap. |
| Natural enemies (predators and parasitoids) | The predatory ladybird Cryptolaemus montrouzieri and parasitic wasps (Leptomastix) - effective under cover at low and medium intensity. | Container growing, glasshouses, winter gardens. |
| Controlling ants and site hygiene | Ants protect mealybugs for the honeydew; controlling them supports predators, and inspecting leaf axils and shoot bases works as prevention. | — |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Systemic insecticide | Taken up by the plant, it reaches the insects despite the waxy shield that protects them from contact sprays; applied by watering or spraying. | In heavy, recurring infestation. |
| Contact insecticide (pyrethroid) | A contact neurotoxin: it mainly hits crawlers and exposed insects, since the wax and hiding places protect the adults; it also harms introduced natural enemies. | Ad hoc, when natural enemies are not used; thorough spray repeated every 7-10 days. |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Atlas of ornamental-plant pests
