Onion thrips
Thrips (Thrips tabaci) suck out the contents of onion leaf cells, leaving silvery streaks. They are worst in warm, dry summers — badly attacked leaves look as if they have been silvered.
Symptom photos
Symptoms
- Silvery-white streaks and flecks on the leaves
- Tiny black specks of droppings on the leaf surface
- Very small, elongated, yellow-brown insects in the leaf sheaths
- Leaves twisting, distorting and drying from the tips
- Heaviest symptoms in the heart of the plant, between the young leaves
What it does to the crop
- Reduced photosynthesis and smaller bulbs
- Growth checked where numbers are high
- Transmission of viruses, including iris yellow spot virus
- Damage opening the way to purple blotch
What encourages it
- Warm, dry weather above 25°C
- Drought and water stress
- Cereals and grasses nearby, once they have been cut
- Many generations a season when the weather suits
Prevention
- Water regularly to limit both damage and numbers
- Use blue sticky traps for monitoring
- Keep distance from cereals and grassland
- Clear crop debris and weeds
- Deep autumn cultivation to destroy overwintering thrips
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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