Spider mites
Leaves get fine pale speckles, turn dull greyish-yellow or bronze and drop. In bad cases there is fine webbing between leaves and stems, with tiny red or yellow mites on the leaf undersides.
Spider mites love warm, dry air: indoors during the heating season, in greenhouses and outdoors in hot, dry summers.
What can you do?
- Give the plant a thorough shower, including the leaf undersides, and repeat every few days.
- Raise the humidity: stand houseplants on a tray of wet clay pebbles, away from radiators.
- Cut off badly affected leaves and shoots.
- In a greenhouse or conservatory, release predatory mites (Phytoseiulus persimilis), which eat the spider mites.
Prevention
Keep the humidity up and water on time, as drought stress makes plants more susceptible. In summer, check under the leaves regularly.
When to watch out: June–September