PEST GUIDE
How to identify and manage onion thrips
Silvery streaks, twisted leaves and reduced bulb growth. Identify the cause, protect the listed crops and use proportionate control.
13 sections
Identification
Onion thrips hide between the upright folds of leaves and are difficult to see without separating them. Silvery streaks, distorted tips and dry-weather flare-ups are more useful field clues than a quick look at the bed.
Slender yellow-brown thrips hide in leaf folds.
The relevant stage and feeding site are: Slender yellow-brown thrips hide in leaf folds. Similar symptoms can come from weather, nutrient stress or another pest. Confirm fresh feeding or the relevant life stage before removing plants or taking control measures.
UK seasonality and monitoring
Onion thrips are most active in warm, dry weather from late spring into summer.
During this period inspect Onions, garlic, leeks and alliums, concentrating on the crop stage and plant parts described above. Note when and where fresh injury appears; old feeding marks can remain after the pest has moved on.
Crops and plants affected
The recorded hosts are Onions, garlic, leeks and alliums. This list identifies plants worth checking; it does not mean every crop is equally vulnerable. Start with the listed plants and inspect the tissue where this pest feeds.
Check affected crops for these signs: Silvery streaks, twisted leaves and reduced bulb growth. Match the symptom to a live pest, larva, egg or characteristic feeding sign before deciding that treatment is needed.
Damage and likely consequences
Silvery streaks, twisted leaves and reduced bulb growth. A small amount of old damage on a vigorous plant may be cosmetic. Continued feeding on roots, seedlings, growing points or edible parts can reduce establishment or yield.
On Onions, garlic, leeks and alliums, judge severity by checking whether injury is fresh and spreading, whether the plant is still growing, and whether the edible part is affected. Avoid removing a crop based on one ambiguous mark.
Prevention
Water consistently during dry weather, rotate alliums and separate folded leaves during inspection.
Control and integrated management
Rinse leaf folds and keep plants evenly watered; remove badly damaged foliage only when healthy leaves remain.
Natural predators and wildlife-conscious choices
Use monitoring and targeted controls rather than routine spraying.
For onion thrips on Onions, garlic, leeks and alliums, use a barrier or hand removal only where it fits the crop and life stage. Keep any cover taut, inspect it for trapped wildlife, and remove it when protection is no longer needed.
Long-term management
Monitor onions, garlic and leeks from late spring and clear allium debris after harvest.
For onion thrips on Onions, garlic, leeks and alliums, record the bed, crop stage and date when fresh damage first appears. Those notes help time protection and monitoring before the same crop stage is vulnerable next season.
Common mistakes
A symptom alone is not a diagnosis. Onion thrips hide between the upright folds of leaves and are difficult to see without separating them. Silvery streaks, distorted tips and dry-weather flare-ups are more useful field clues than a quick look at the bed. Look for a matching live pest or fresh feeding sign before intervening.
Thrips hide between upright leaves, and dry-weather stress can make their feeding look worse.
If damage continues
Recheck Onions, garlic, leeks and alliums where new injury is appearing, including the hidden feeding site: roots, folded leaves, leaf undersides, flowers or fruit as appropriate. If identification remains uncertain, photograph a live specimen alongside the damage and ask an allotment association or horticultural adviser.
If the recommended control (Wash foliage and remove badly affected leaves where practical.) has not helped, confirm that it was fitted or applied at the right crop stage and that fresh damage is still occurring. Old marks do not heal when the pest has gone.
Frequently asked questions
Why are onion thrips hard to spot between leaves?
Onion thrips hide between the upright folds of leaves and are difficult to see without separating them. Silvery streaks, distorted tips and dry-weather flare-ups are more useful field clues than a quick look at the bed. Check Onions, garlic, leeks and alliums, especially at the feeding site described above. Wash foliage and remove badly affected leaves where practical.
When should I start checking for onion thrips?
Onion thrips are most active in warm, dry weather from late spring into summer.
How can I tell whether onion thrips is still active?
Look for fresh damage and the relevant life stage. Silvery streaks, twisted leaves and reduced bulb growth. Old marks may remain after the pest has moved on.
What wildlife-conscious approach works for onion thrips?
Use monitoring and targeted controls rather than routine spraying. Check covers and traps frequently, and remove them when the vulnerable crop stage has passed.