GrowingHQ
Stems

White fluff in the leaf joints

Small tufts of white, waxy, cotton-wool-like material packed into the angle where a leaf meets the stem, under leaf bases, or around the top of the root ball. Unlike a powdery coating spread over the leaf surface, this is concentrated in sheltered crevices — which is both the identification and the reason it survives casual cleaning.

What causes it, and how to tell them apart

Work down the list making the observation under each heading. GrowingHQ will not guess which one you have — the observation is the answer.

  1. Mealybugvery common
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Mealybug

    Checked 2026-08-13

    How to tell

    The fluff can be lifted away to reveal a soft grey-pink insect beneath it, and it sits in crevices rather than lying on open leaf surfaces.

    source

    Horticultural consensusmoderate confidence

    No external citation — see the evidence type above.

    Checked 2026-08-13

    If it is this, do first

    Isolate the plant from the rest of the collection and wipe every leaf joint out with a damp cloth or cotton bud, repeating weekly.

    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Mealybug — control

    Checked 2026-08-13

  2. Powdery mildewuncommon
    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Powdery mildew

    Checked 2026-08-13

    How to tell

    A powdery film spread evenly across the open leaf surface rather than tufted in the joints, and nothing underneath it when rubbed away.

    source

    Horticultural consensusmoderate confidence

    No external citation — see the evidence type above.

    Checked 2026-08-13

    If it is this, do first

    Improve airflow around the plant and remove the worst-affected leaves.

    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Powdery mildew — control

    Checked 2026-08-13

Commonly reported on