How to identify and manage thrips

UK seasonality and monitoring

Most active in warm greenhouse and polytunnel conditions.

During this period inspect Chillies, peppers, cucumbers, onions and protected crops, 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 Chillies, peppers, cucumbers, onions and protected crops. 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, distorted growth and black specks of droppings. 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, distorted growth and black specks of droppings. 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 Chillies, peppers, cucumbers, onions and protected crops, 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

Inspect flowers and leaf folds, remove crop debris and use monitoring cards where appropriate.

Control and integrated management

Wash foliage and consider biological control under cover only when the crop and conditions suit it.

Natural predators and wildlife-conscious choices

Avoid broad sprays that remove predatory mites and other helpers.

For thrips on Chillies, peppers, cucumbers, onions and protected crops, 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

Quarantine new plants and monitor warm protected crops; avoid broad sprays that remove predatory mites.

For thrips on Chillies, peppers, cucumbers, onions and protected crops, 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. Thrips are narrow, tiny insects that hide in flowers and folded leaves. Silvery scars and small black faecal specks are typical. Tap a flower over white paper to reveal moving insects before treating. Look for a matching live pest or fresh feeding sign before intervening.

Silvering can remain after thrips have gone; confirm live insects or fresh feeding before treating again.

If damage continues

Recheck Chillies, peppers, cucumbers, onions and protected crops 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 use biological controls under cover when suitable.) 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