Whitefly
A cloud of tiny white flies of 1–2 mm rises when you touch the plant. Flat, pale green larvae sit on the leaf undersides; the leaves become sticky, turn yellow and get black sooty mould.
Whitefly thrives in warm, sheltered spots such as greenhouses and homes, and outdoors on brassicas and tomatoes in warm summers.
What can you do?
- Hang yellow sticky traps just above the plants to catch the adults.
- Spray the leaf undersides with water or an insecticidal soap to hit the larvae.
- In a greenhouse, release the parasitic wasp Encarsia formosa, which lays its eggs in the larvae.
- Remove badly infested lower leaves.
Prevention
Ventilate the greenhouse well, check new plants and clear away old brassica and tomato plants after harvest. Don’t put infested houseplants next to your seedlings.
When to watch out: June–October