Diagnose by symptom
Sticky leaves (honeydew)
A sticky, shiny film is honeydew from sucking pests; black sooty mould often grows on it. Culprits:
Pests
Aphids
Small (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leave…
PestMealybugs
Insects covered in a white, cottony, waxy coating, gathering in leaf axils, at the base of shoots and on the underside o…
PestArmoured and soft scale insects
Immobile, brown or yellowish shields (1-4 mm) attached to stems and the underside of leaves, especially along the veins.…
PestGreenhouse whitefly
Tiny (1-2 mm) white insects resembling minuscule moths that rise in a cloud when the plant is disturbed. They feed on th…
PestPear psylla
Small sucking insects whose adults resemble tiny cicadas and jump off the shoots when disturbed. The flat, yellowish nym…
Frequently asked questions
Why are my plant's leaves sticky?
A sticky, shiny film is honeydew – a sugary secretion from sap-sucking pests. It is usually caused by aphids, whiteflies, mealybugs and scale insects. Inspect the leaf undersides and shoots where these pests gather.
Where does sticky honeydew come from?
Honeydew is the excess sugar excreted by pests feeding on phloem sap (aphids, whiteflies, scale insects). The droplets settle on leaves below the feeding insects and on the pot or floor. It is not a disease itself, but signals a pest infestation and encourages sooty mould.
What is the black coating on sticky leaves?
The black, sooty coating is sooty mould – fungi that grow secondarily on the honeydew. It does not attack plant tissue, but coats the leaves and reduces light, weakening photosynthesis. It clears once you control the pests producing the honeydew and wash the film off with lukewarm water and mild soap.