Scale insects
Brown or grey bumps of 1–5 mm stuck to stems and along the veins on leaf undersides; you can scrape them off with a fingernail. Leaves become sticky, turn yellow and drop.
Their hard shell protects them well; they thrive in warm, dry indoor air and on weakened shrubs and trees.
What can you do?
- Scrape or brush the scales off with a soft toothbrush and soapy water.
- Then wipe stems and leaves with a cloth dampened with surgical spirit or spray with an insecticidal soap; repeat for a few weeks.
- Cut out badly infested branches and put them in the general waste, not on the compost heap.
- Outdoors, parasitic wasps, ladybirds and tits eat many of them, so don’t use poison.
Prevention
Give houseplants enough light and air that isn’t too dry, and inspect them closely now and then. A strong, well-cared-for plant is attacked less readily.
When to watch out: April–September