Thrips are tiny, slender insects that rasp at plant tissue and can scar leaves, distort new growth, damage flowers and pollen, and spread plant viruses. They are easy to miss until the damage shows. This is a general guide — species, host plants and the right response vary, so treat it as the framework and follow guidance specific to your plant and any product you use.
What thrips are
Thrips are minute insects (often 1–2 mm / less than 1/16 inch) with narrow bodies and fringed wings. Both the adults and the wingless nymphs feed by puncturing plant cells and sucking out the contents, which leaves a characteristic silvery or bronzed scarring. Many species exist; some specialise on particular plants, while others feed on a wide range of ornamentals, vegetables and fruit. Because they are so small and often hide inside buds, folded leaves and flowers, populations can build before you notice them.
Common visual symptoms
- Silvery, greyish or bronzed streaking and stippling on leaves, often with tiny black dots (their droppings).
- Distorted, curled or scarred new growth.
- Flecked, streaked or discoloured flower petals; buds that fail to open properly.
- Scarred, deformed or russeted young fruit on susceptible plants.
- Tiny slivers that move quickly when a flower or leaf is disturbed or tapped over white paper.
Leaves vs flowers vs fruit
- Leaves show silvery scarring and black specks where cells have been emptied.
- Flowers and buds can be streaked, flecked or deformed, and thrips often shelter deep inside them.
- Young fruit can be scarred or russeted where thrips fed on the developing surface — see the flowering/fruiting section below.
Damage they cause
- Cosmetic and structural scarring that weakens and disfigures growth.
- Reduced vigour when populations are high.
- Damaged pollen and flowers, which can reduce pollination and fruit set.
- Virus transmission — several thrips species spread plant viruses (such as tospoviruses) as they feed, which can be more serious than the direct feeding damage.
Conditions that favour them
- Warm, dry weather, which speeds up their short life cycle.
- Sheltered spots — greenhouses, indoors and dense plantings where populations build undisturbed.
- Continuous soft new growth and flowering, which gives them food and shelter.
- Nearby infested plants or weeds acting as a reservoir.
Thrips on flowers and fruit set
Thrips are one of the pests most directly linked to poor fruiting, because they feed on flowers, pollen and developing fruit, not just leaves. Feeding inside blooms can damage pollen and flower parts, so pollination fails or fruit sets poorly; feeding on newly set fruit leaves scarring, russeting or deformity. On plants such as peppers, eggplant, many ornamentals and African violets, a flowering-time thrips problem can be mistaken for a pollination failure. If a plant flowers but sets little fruit and the blooms are flecked, streaked or hiding tiny insects, thrips may be part of the cause — see why plants flower but don’t produce fruit.
Monitoring
Thrips are small and secretive, so monitor deliberately. Tap flowers or shoot tips over a sheet of white paper and watch for fast-moving slivers. Coloured sticky traps (blue is often used for thrips, yellow catches a wider range of flying pests) help you detect them early and track whether numbers are rising or falling. Check the most susceptible plants regularly, and inspect new plants before bringing them indoors or into a greenhouse.
Treatment principles
- Act early and physically first. Remove and dispose of badly infested buds, flowers and shoot tips; a firm spray of water can knock numbers down on sturdy plants.
- Encourage or introduce natural enemies. Predatory mites, lacewings, minute pirate bugs and other beneficials feed on thrips and are widely used, especially under cover.
- Use sticky traps for monitoring and to reduce adult numbers.
- If using a product, several lower-toxicity options exist (for example insecticidal soaps, horticultural oils, and spinosad-based or other products). No single product is right for every plant or every thrips species, and thrips are prone to resistance — choose one labelled for your plant and pest, follow the label exactly, rotate modes of action, and never exceed labelled rates. Avoid spraying open flowers when pollinators are active.
Sanitation
Remove spent flowers and heavily infested growth, clear weeds that host thrips, and dispose of infested material rather than composting it near susceptible plants. Isolate and inspect new arrivals, since thrips are commonly brought in on bought-in plants.
Prevention
- Inspect new plants before introducing them, especially indoors or under glass.
- Use sticky traps as an early-warning system on vulnerable plants.
- Keep plants well grown but avoid excess soft, lush growth.
- Control host weeds nearby.
- Support natural predators by avoiding broad-spectrum sprays that kill beneficials.
Repeated monitoring
Thrips have short, overlapping generations, so a single treatment rarely ends the problem. Keep checking susceptible plants and traps, and repeat control as the label allows — rotating products — until numbers fall and stay down.
Common mistakes
- Waiting until leaves are heavily scarred before looking for the cause.
- Relying on one product repeatedly, which drives resistance.
- Ignoring flowers and buds, where thrips shelter and do fruiting damage.
- Spraying open blooms when pollinators are active.
- Bringing in infested new plants without inspecting or isolating them.
Quick questions
How do I know it’s thrips and not spider mites? Spider mites cause fine pale stippling and sometimes webbing; thrips leave silvery scarring with tiny black droppings, and you may see slivers moving when you disturb flowers. See spider mites.
Can thrips stop my plant fruiting? Yes — by damaging pollen, flowers and young fruit they can reduce or scar the crop, which is why they feature in fruit-set problems.
Are all thrips harmful? No. Some species are predatory or harmless; the pest species are the ones scarring foliage, flowers and fruit or spreading viruses.
Related guides
- Why is my plant flowering but not producing fruit?
- All plant pests & protection
- Spider mites · mealybugs · powdery mildew · aphids
- Choosing a plant sprayer for applying treatments · all plant pests & protection
- Sticky traps & pest monitoring – detect and track these pests early.
