Scale insects: how to recognise and treat it

Pest

Symptoms

Small round or oval bumps on stems and along leaf veins, mostly underneath, that do not move and look like shells or scabs.
Sticky honeydew on leaves or on surfaces below the plant, often with black sooty mould.
Some species lay eggs under white, waxy, cotton-like fibres on stems or leaf undersides.
Heavy infestations cause yellowing, leaf drop, poor growth and dieback.

Scrape scales off with a fingernail, toothpick or soft toothbrush; wash broad leaves with a soft cloth and mild soapy water.
Dab single scales with a cotton swab dipped in rubbing alcohol; do not wet whole leaves with it.
Horticultural oil, insecticidal soap or neem oil with full coverage; they kill mainly the young crawlers, so repeat over 2–4 months as the label allows.
In a greenhouse or garden, the nematode Steinernema feltiae controls soft scale; ladybirds and parasitic wasps also eat scales.

A systemic insecticide with flupyradifurone, approved for ornamentals and some edibles; it also kills beneficial insects, so treat only after the other methods fail, keep off open flowers and follow the label.
Avoid broad-spectrum pyrethroid sprays against scale — they kill the scales' natural enemies and can trigger spider mite outbreaks.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Inspect new plants closely before buying and keep them apart from your other plants for a while — scale usually arrives on new plants.
Control ants on infested plants; they collect honeydew and protect scales from their natural enemies.
Give plants good care and rinse dusty foliage; healthy plants tolerate light populations.
Replace heavily infested plants — this is often simpler than eliminating the scale.

Figures checked against these sources.