Why does my moth orchid have sticky residue on the leaves or the floor?

On a moth orchid this is a clear, tacky film on a leaf, on a flower stem or on the windowsill or table underneath the plant. It feels sticky to the finger. Look for small bumps or white fluff nearby, because the film is only the evidence.

The most likely cause, as the entry says, is scale or mealybugs on the undersides of the leaves and on the flower stems. The RHS describes moth orchids as generally untroubled by pests and diseases but says they may attract mealybugs, and the NC State plant toolbox lists scale and mealybugs among the problems that may appear. Both feed on sap and excrete the sugar, which is the sticky film.

To confirm it in a minute, run a finger along the underside of a leaf and along the flower stem, and look at the leaf joints and the crown. Scale are small brown or fawn bumps, two to five millimetres, that do not move and lift off with a fingernail with a soft body underneath. Mealybugs are white waxy fluff in the joints.

Another cause worth ruling out is aphids. They gather on the newest growth and the flower buds, the stickiness is worst directly below them, and ants are often in attendance. Scale and mealybugs are found along the stems, in the leaf joints and under the leaves instead.

The film wipes away, but new patches keep appearing until the insects are gone, which is why the page on sticky residue asks for repeated treatment. Judge it by whether new sticky patches stop appearing over a month, after which the plant carries on as before.

What this plant wants

The fix

Wipe every surface with a damp cloth, check the leaf joints, and treat weekly with an insecticidal soap until nothing new appears.

Read on

Sticky residue on the leaves or the floor

The same sign on any plant, with the causes in the order they are likely.

Moth orchid care

Light, water, feeding, repotting and the rest of the entry.

Check it in the diagnoser

Opens with the plant, the part and the sign already chosen.