Tomato: sticky leaves, or a sticky surface below the plant

What it is likely to be on tomato

1. Whitefly

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Agriculture and Horticulture Development Board — AHDB: Glasshouse whitefly

   Checked 2026-08-13

   Small white moth-like insects on the undersides of leaves that rise in a cloud when the plant is disturbed — a sign so distinctive that it settles the identification on its own. The scale-like immature stages stay fixed to the leaf and are what actually does the feeding.

   Points towards it

   • · glasshouse whitefly cannot survive a British winter outdoors and is overwhelmingly a protected-crop problem on exactly these three
   • · the adults sit under the leaves and rise in a cloud when the plant is moved

   Argues against it

   • · webbing means spider mite, which produces no honeydew at all — this rules it out entirely.
   • · an outdoor plant in Britain is far more likely to have aphids than whitefly

   Check this next

   Shake the plant and watch. Glasshouse whitefly rises as a cloud of small white insects and settles again within seconds — nothing else on these crops does that. Then turn a leaf over: the immobile scale-like nymphs are the stage doing most of the feeding, and they are what makes the fruit trusses sticky and later black with sooty mould.

   What to do now

   Hang yellow sticky traps at plant height to monitor rather than to control, and introduce the parasitic wasp Encarsia formosa early while numbers are low — it is the established biological control for protected crops and works poorly once the population is large. Ventilate well and remove the lowest leaves where the nymphs concentrate.

   ·source

   Sourced guidancehigh confidence

   • Agriculture and Horticulture Development Board — AHDB: Glasshouse whitefly — biological control

   Checked 2026-08-13

2. Aphids

   Candidate 2common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Aphids

   Checked 2026-08-13

   Sap-feeding insects that cluster on soft growing tips and leaf undersides, distorting new growth and leaving sticky honeydew that blackens with sooty mould. Most garden infestations are transient and end when predators catch up.

   Points towards it

   • · aphids feed on the softest tissue, which on a cordon crop is the growing tip
   • · a colony builds on one tip or one truss rather than across the whole plant

   Argues against it

   • · mites make webbing and no honeydew — this rules it out entirely.

   Check this next

   Look at the growing point rather than under the leaves. Aphids cluster on the top few centimetres of the stem and on the flower truss, they are visible without a lens, and they do not fly up when disturbed — where whitefly are spread across the leaf undersides down the whole plant and take off immediately.

   What to do now

   Pinch out or wipe off the affected tip with a damp cloth; on a cordon tomato that tip was going to be removed eventually anyway. Leave the rest alone for a fortnight — ladybird and hoverfly larvae find indoor aphid colonies quickly if nothing is sprayed, and an early spray removes them along with the aphids.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Aphids — control

   Checked 2026-08-13

3. The plant's own resin

   May be normalvery common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Tomatoes — growing

   Checked 2026-08-13

   Not a problem. Tomatoes, and to a lesser degree aubergines and some herbs, are covered in glandular hairs that release a sticky aromatic resin when brushed. It transfers to hands and clothing, smells strongly of the plant, and is present on a completely healthy specimen — it is the reason a tomato plant smells of tomato. It is routinely mistaken for honeydew from an insect that is not there.

   Points towards it

   • · there is nothing to find because there is nothing there
   • · the glandular hairs cover every stem and leaf underside equally
   • · the resin is strongest on the growing point and the side shoots

   Argues against it

   • · an insect on the plant means the stickiness has a source other than the plant — this rules it out entirely.

   Check this next

   Look at the UPPER surface of a leaf low down the plant, and at whatever the pot is standing on. Honeydew falls, so it collects on the leaves and the floor beneath the insect; the plant's own resin is on the stems and leaf undersides where the hairs are, smells strongly of tomato, and leaves the floor clean. A tomato that is sticky to handle and has nothing on it is a normal tomato.

   What to do now

   Nothing at all. Wash your hands and carry on tying in — the stain is stubborn and harmless. This is the single commonest reason a healthy tomato in flower gets sprayed, and spraying a crop in flower reaches the pollinators the fruit depends on.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Tomatoes — growing

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on tomato — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general sticky leaves, or a sticky surface below the plant page lists causes across all plants, and the Tomato profile lists the problems it is prone to.