What are the white cottony spots on my plant?

Almost always mealybugs. They cluster in leaf axils, under leaves and along stems, coating themselves in a white waxy fluff that repels water and most sprays. The fluff is the insect's covering, not a fungus.

How do you get rid of scale insects?

Physically first — scrape or wipe the adults off, since their shells block sprays. Then treat the crawler stage, which is vulnerable, with horticultural oil or insecticidal soap repeated every week for a month to catch each new hatch.

White Fuzz, Bumps and Sticky Leaves

By IdentifyThese Editorial · Reviewed October 2026 · 3 min read

Both insects spend most of their lives motionless, which is why people find the damage long before they find the cause.

Telling them apart

Mealybugs look like specks of cotton wool, typically in the crevices where a leaf meets the stem. Move one with a cocktail stick and it walks, slowly. Underneath the wax is a soft flat-oval pinkish insect.

Soft scale looks like small brown or tan bumps stuck along stems and leaf veins. They appear to be part of the plant. Push one with a fingernail and it lifts off, leaving a slightly damp mark.

Armoured scale is smaller, flatter and harder, more like a limpet, and the shell separates from the insect underneath.

	Mealybug	Soft scale	Armoured scale
Appearance	White cotton fluff	Brown domed bumps	Flat hard discs
Moves	Slowly, yes	Adults do not	Adults do not
Honeydew	Copious	Copious	None
Where	Leaf axils, roots	Stems, leaf veins	Stems, leaf undersides
Sprays reach it	Poorly, wax repels	Poorly, shell blocks	Very poorly

The honeydew trail

Both mealybugs and soft scale excrete sugar. It lands on leaves below as a sticky film, and black sooty mould grows on it.

That means sticky leaves are frequently the first sign, and the insects are above the sticky part rather than on it — a distinction covered in sticky leaves and honeydew. Looking on the sticky leaf finds nothing; looking on the stem above it finds the colony.

Why the first treatment fails

Because both are built to shed sprays. Mealybug wax is hydrophobic and armoured scale sits under a shell it is not attached to, so a contact spray reaches neither.

And because the eggs are not affected. A treatment that kills every adult on the plant leaves hundreds of eggs that hatch over the following fortnight, and the plant looks clear for a week before the problem returns worse.

What actually works

Physical removal first. A cotton bud dipped in rubbing alcohol dissolves mealybug wax on contact and kills the insect under it. For scale, a fingernail, an old toothbrush or a blunt knife takes the adults off.

Then oil, repeatedly. Horticultural oil or a dilute soap spray, covering every surface including leaf undersides and stem junctions, once a week for four weeks. The repetition is what catches successive hatches, and stopping after two applications is the commonest reason an infestation returns.

Isolate the plant. Both spread readily to neighbours, and crawlers travel further than people expect.

Check the roots. Root mealybugs exist, look like white powder on the root ball, and explain plants that keep reinfesting after the visible bugs are gone.

Knowing when it is over

Four weeks with no new insects on a plant checked weekly. Sticky residue alone is not evidence of an active infestation, since existing honeydew stays where it landed until it is washed off.

Wipe the leaves clean at the start of treatment so any new stickiness means something.

When to stop trying

A badly infested plant with scale in every crevice can take months and may never be fully clear, and it is a reservoir for everything else in the room.

For a common plant, a clean cutting from an unaffected stem is faster and more certain than treating the parent. For anything valuable or sentimental, persistence works — but it means a diary entry every week for a month, not a single afternoon.

Problems referenced

MealybugsTreatable Scale InsectsTreatable Sooty MoldMostly cosmetic

Check these two things first

Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.

Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.