Scale Insects
TreatablePest · spreads to other plants · also called armoured scale, soft scale
Scale insects are missed for months because they do not look like insects — people take them for bark texture or a growth on the stem. They spend almost their whole life fixed in one place under a protective shell, which also makes them resistant to most sprays.
What it looks like
Small immobile bumps along stems and leaf veins, brown, tan or white, looking far more like part of the plant than like an insect. Scrape one off with a fingernail and there is a soft body underneath. Sticky honeydew and black sooty mould usually accompany them.
How to confirm it
- Immobile bumps that scrape off with a fingernail, leaving a soft body.
- Lined up along stems and the midribs of leaves.
- Sticky leaves below where they are feeding.
- They do not move, which is exactly why they are mistaken for plant tissue.
What to do
- 1Scrape them off physically, or dab each with a cotton bud dipped in rubbing alcohol.
- 2Horticultural oil smothers them, which works where contact insecticides fail against the shell.
- 3Prune out heavily encrusted stems.
- 4Repeat treatment every one to two weeks; the mobile crawler stage is what you are actually catching.
What it gets confused with
One observation settles each of these.
Mealybugs are covered in white cottony wax and can move slowly. Scale is hard, flat and stationary.
Preventing it next time
- Inspect stems and leaf undersides of new plants.
- Wipe houseplant leaves periodically — it catches infestations early.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.