White Fluffy Stuff on Your Plant — Mealybugs and How to Remove Them

Photo: Maja Dumat from Deutschland (Germany), CC BY 2.0, via Wikimedia Commons

Small white blobs that look like specks of cotton wool, tucked into leaf joints and the undersides of leaves, are mealybugs. They are insects wearing a waxy coat, and that coat is why they survive most sprays: water simply runs off it.

Mould or insect?

Push one with a cocktail stick. A mealybug moves, or at least detaches as a distinct oval body leaving a faint smear. Mould smears flat and has no shape underneath. If nearby leaves are sticky or shiny, that settles it — mealybugs excrete honeydew, mould does not.

Why they are so persistent

Females hide their eggs in the same white wax, deep in crevices, in leaf sheaths, and commonly below the soil line on the roots. Treating only the visible insects is why the problem appears to return three weeks later; it never left.

Removing them

1. Isolate the plant. Mealybugs crawl between touching leaves.
2. Dab each one with a cotton bud dipped in 70% isopropyl alcohol. The alcohol dissolves the wax and kills on contact. This is tedious and it is the step that actually works.
3. Then wash the whole plant with insecticidal soap, covering leaf joints, stem bases and the undersides.
4. Check the roots if it keeps recurring. Root mealybugs look like white powder around the root ball; the fix is bare-rooting, rinsing, and repotting into fresh compost.
5. Repeat weekly for a month. Eggs hatch in waves.

Prevention

Quarantine every new plant for two to three weeks — mealybugs arrive on new purchases far more often than they appear spontaneously. Inspect the crevices of orchids, succulents and cacti specifically, because their tight growth points are the ideal hiding place.

Not sure that's what you have?

Symptoms overlap, and the wrong treatment wastes weeks. Photograph the affected leaf with Sherleaf and you get the diagnosis, a severity rating and a treatment plan in about ten seconds.