Scale insects

Adult scale insects barely move: they sit under a hard or waxy shell, sucking sap. That shell is why sprays alone often fail — you have to remove the adults by hand.

How to tell

• Oval or round bumps, 1–5 mm, brown, tan or grey, along stems and the undersides of leaf veins. They look like part of the plant until you scrape one off.
• Sticky, shiny leaves and floors below the plant (honeydew), sometimes with black sooty mould.
• Yellowing leaves, leaf drop and slowed growth.

Ficus, palms, citrus, orchids and bird of paradise are common hosts.

How to get rid of them

1. Isolate the plant.
2. Remove the adults: scrape them off with a fingernail or a soft toothbrush, or wipe stems and leaves with a cloth dipped in soapy water.
3. Dab remaining ones with a cotton swab dipped in rubbing alcohol.
4. Spray with horticultural oil or a neem product, which smothers young crawlers and the ones you missed, or with insecticidal soap. Cover stems and leaf undersides. Keep oil-sprayed plants out of direct sun and heat until dry, or the leaves can burn.
5. Repeat every 7–10 days for six to eight weeks, checking and scraping each time. Eggs under the shells keep hatching for weeks.

Prune off heavily infested stems. Wash the sticky residue from the leaves so they can photosynthesise.

How to prevent them

Check stems and leaf veins of new plants, especially ficus and palms, keep new arrivals apart for a couple of weeks, and wipe leaves regularly: you'll spot the first bumps early.