Guides
Why are my plant leaves sticky?
Sticky leaves usually mean sap-sucking insects are feeding above them. They excrete honeydew, which falls onto leaves, floors, cars or furniture below. Follow the sticky area upward to find the pest.
Check the growth above
Honeydew falls, so the insect producing it is on the growth above the sticky leaf. Follow the stickiness up the plant to the shoot tips and young stems, and check the undersides. On a sticky patio or car, look at the plant growing overhead.
Work down the list
Aphids
- What you would see
- Dense colonies of green, black or grey insects packed onto shoot tips, flower buds and the undersides of young leaves, from May onwards.
- The check
- Look at the newest growth first. Aphids gather on the softest tissue, and ants running up the stem often lead to them.
Scale insects
- What you would see
- Immobile brown, yellow or white bumps along stems and the main veins, looking like part of the bark, on bay, citrus, camellia, holly and many houseplants.
- The check
- Run a thumbnail along a stem. Scale insects pop off. The young stages are flat, translucent and easy to miss.
Mealybugs
- What you would see
- White waxy tufts in leaf joints and under leaves on a houseplant, with the stickiness worst directly below them.
- The check
- Squash one and look for an orange or pink smear, which confirms an insect rather than a fungus.
Whitefly
- What you would see
- Tiny white insects rising in a cloud from the undersides when the plant is knocked, in a greenhouse or on indoor plants.
- The check
- Turn a lower leaf over. The flat, immobile young stages produce most of the honeydew, and they are easier to miss than the adults.
A tree overhead
- What you would see
- Sticky spotting on a car, a patio, garden furniture or the plants under a lime, sycamore, cherry or willow, from June to September.
- The check
- Look up. Lime aphids on a mature lime can produce enough honeydew to make the pavement tacky. A tree that size usually cannot be treated and usually does not need treatment. Move the car and garden furniture instead.
Sooty mould
- What you would see
- Leaves that were sticky a fortnight ago now covered in a black or dark grey film that wipes off to leave sound green leaf.
- The check
- Wipe a leaf. Sooty mould grows on the honeydew rather than on the plant, so removing the insect stops the black returning.
Naturally sticky leaves or stems
- What you would see
- Sticky glandular hairs over the stems and leaves of a plant that has always had them, with no insects anywhere.
- The check
- Feel a new leaf on an undamaged part of the plant. Salvias, petunias, tomatoes, tobacco plants and sundews naturally have sticky hairs. If the whole plant is evenly sticky and there are no insects, this may be normal.
Still not sure which one it is? Photograph the leaf and compare it against the full library.