Thrips
Silvery-grey, shiny patches on the leaves with tiny black dots (droppings). New leaves and flowers grow distorted; you mostly see the slender 1–2 mm insects when you tap the plant over white paper.
Thrips suck cells empty and multiply quickly in warm, dry conditions, indoors and in greenhouses, but also on leeks and onions in dry summers.
What can you do?
- Give the plant a thorough shower and raise the humidity.
- Hang up blue sticky traps to catch flying thrips and monitor the infestation.
- Cut off affected flowers and badly damaged leaves.
- In a greenhouse or indoors, release predatory mites (Amblyseius) against the larvae.
Prevention
Keep the air from getting too dry, water enough and check new plants. Outdoors, a varied garden with plenty of natural enemies such as predatory bugs helps.
When to watch out: May–September