Sticky leaves, or a sticky surface below the plant
Leaves feel tacky, and the floor, shelf or leaves below the plant have a shiny sticky film. The stickiness is honeydew — sugar the plant made, drunk by a sap-feeding insect and excreted almost unchanged — so its presence proves an insect is feeding even when nothing is visible. A black sooty mould often grows on it afterwards, which is a consequence rather than a separate problem.
Described view
The underside of a tomato leaf held up to the light showing both culprits at once: a dense cluster of soft-bodied green aphids along the midrib, and separately the tiny flat white-winged adults and pale scale-like nymphs of whitefly, with the sticky honeydew shine visible on the leaf surface below them
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.
- Aphidsvery common
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Aphids
Checked 2026-08-13
How to tell
Clusters of soft-bodied green, black or pink insects packed on the youngest shoots and flower buds, visible without magnification.
source
Horticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
If it is this, do first
Rub or wash the colonies off with a jet of water, concentrating on the growing tips where they gather.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Aphids — control
Checked 2026-08-13
- Whiteflycommon
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Glasshouse whitefly
Checked 2026-08-13
How to tell
A cloud of tiny white insects rises when the plant is shaken, then settles back on the leaf undersides.
source
Horticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
If it is this, do first
Hang yellow sticky traps to gauge the population, and check leaf undersides for the flat immature stages that do the feeding.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Glasshouse whitefly — control
Checked 2026-08-13
- Scale insectcommon
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Scale insects
Checked 2026-08-13
How to tell
Immobile brown or straw-coloured bumps along the stems and the midribs, which can be scraped off with a fingernail.
source
Horticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
If it is this, do first
Scrape them off by hand and check every stem and leaf vein; the shells protect them from most sprays.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Scale insects — control
Checked 2026-08-13
- Mealybugcommon
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Mealybug
Checked 2026-08-13
How to tell
White waxy fluff packed into leaf joints and under leaf bases, looking like small tufts of cotton wool.
source
Horticultural consensusmoderate confidence
No external citation — see the evidence type above.
Checked 2026-08-13
If it is this, do first
Wipe the colonies out of the leaf joints with a damp cloth or cotton bud, and repeat weekly as eggs hatch.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Mealybug — control
Checked 2026-08-13
Where GrowingHQ holds more for one plant
This page lists the causes across every plant. The plants below are the ones where something about that plant changes the answer — different candidates, or a different observation that separates them.
Vegetables
- Aubergine: sticky leaves, or a sticky surface below the plant — 2 candidates specific to aubergine
- Tomato: sticky leaves, or a sticky surface below the plant — 3 candidates specific to tomato
Fruit
- Blackcurrant: sticky leaves, or a sticky surface below the plant — 2 candidates specific to blackcurrant
Houseplants
- Monstera: sticky leaves, or a sticky surface below the plant — 2 candidates specific to monstera