Lice on a lemon tree: aphid, scale insect or mealybug?
One photo, a few follow-up questions, and you know which of the three sap-sucking groups is sitting on your citrus plant, always with the confidence level stated.
Upload a photo and start the diagnosis →Why the infestation usually gets the wrong name
Something is sticky on the lemon tree, the leaves shine, and somewhere small creatures are sitting. For almost everyone that means lice. The trouble is that this one word covers three completely different groups of insects, which multiply differently, sit in different places and have to be handled in different ways.
Mistaking one for the other costs weeks. If you work against aphids while scale insects are actually fixed under the leaf axils, you wipe leaves for a month and wonder why the problem comes back. The other way round, a short visit of aphids on the new shoots is sometimes treated with heavy effort although predators would have settled it.
In Central and Northern Europe citrus plants usually live in pots and move into winter quarters in autumn. Dry air, little light and no natural enemies make that the perfect starting point for sap suckers. Leaf drop, yellow blotches and sticky coating then appear at the same time, and no single symptom tells you the cause any more.
Aphids: soft, mobile, on the youngest growth
Aphids sit where the tissue is soft: on the newest shoots, on flower buds, on the underside of freshly unfolded leaves. They are soft bodied and pear shaped, green, yellowish, brown or black, and they move when you tap the leaf.
A typical sign is curled and deformed young foliage, plus pale cast skins that look like small empty insects. Colonies build up fast, which also means they are found fast by ladybird larvae, lacewings and parasitic wasps.
Scale insects: firm bumps that will not wipe off
You recognise scale insects by the fact that nothing moves. The females sit tight on twigs, along the midrib and on the leaf underside as brown, grey or yellowish bumps, flat or shaped like a tiny cup. Eggs and crawlers hide under that shield.
The fingernail test helps: if the bump pushes off under light pressure and leaves a moist mark, it was a living insect and not a piece of rough bark. Because they never move, scale insects are the reason an infestation can stay unnoticed for months.
Mealybugs: white waxy tufts in the leaf axils
Mealybugs give themselves away through white waxy flakes that look like small cotton balls in leaf axils, in branch forks and around the root collar. Next to them you find fine white threads and a greasy film.
They are mobile, they wander slowly, and they prefer exactly the places a cloth never reaches: under bark scales, along the rim of the pot, in the top layer of the substrate. That is why they often return after purely mechanical cleaning.
What honeydew, sooty mould and ants tell you
All three groups excrete honeydew, so a sticky leaf surface alone identifies nothing. What follows is often a black film of sooty mould, which does not attack the tissue but blocks light on the leaf.
Ants running up and down the trunk are a hint, not a diagnosis: they harvest honeydew and defend the producers. The useful question is always where the sticky layer starts, because that is where the colony sits.
What Dr. Phyto delivers, and what it does not
You get a named diagnosis with a stated confidence level and a dated plan with single steps and check dates. The basis is a verified European knowledge base, not the guesswork of a general chatbot.
Dr. Phyto names no plant protection product, because approvals differ from country to country and an approved use in one state can be unlawful in the next. For the choice of a product the responsible national authority applies, together with the approved use, dosage and, for plants that bear fruit, the waiting periods and residue rules written into that approval. For individual cases we recommend talking to an agronomist or asking us directly.
And if a plant is beyond saving, that is said out loud. No recovery is promised here.
Who this identification is built for
Home gardeners with a potted lemon on the balcony, in the garden or in the living room get a clear name instead of a guess. Professional growers in viticulture, fruit growing, greenhouses and market gardening get a fast first sorting before taking a decision.
Authorities and municipalities use it for early detection from citizen photos and for cases with reporting duties under EU law. Agronomists and advisers use it as a quick second opinion and for differential diagnosis.
Can I separate the three groups with the fingernail test alone?
It gets you a long way. A bump that stays rigid and detaches as a shield points to scale insects, a soft insect that moves points to aphids, a white waxy tuft points to mealybugs. Mixed infestations and very young crawlers remain hard to read, which is why the diagnosis always comes with a confidence level.
Which product should I spray on my lemon tree?
We do not name products. Only plant protection products approved in your own country may be used, and only in the approved use and dosage. Which that is belongs to the responsible national authority. For plants bearing fruit the waiting periods and residue rules of the approval also apply. Ask an agronomist or contact us directly for your case.
My tree is dropping all its leaves. Is it still worth treating?
Maybe, maybe not. Leaf drop on citrus often has several causes at once, for example sap suckers plus a dark and cold winter position plus waterlogging. The plan names what is treatable and what is not, and if the plant is lost the report says so instead of selling hope.
What if the pest is a notifiable organism?
Some pests occurring on citrus are listed as quarantine organisms under Regulation (EU) 2019/2072. In that case the reporting duty stands and cannot be played down. Infested material must not simply be disposed of, moved or sold. The competent national authority has to be informed, and it decides on the next steps.