Thrips
You see the silvery streaks long before the insect. The black fecal specks are what separate thrips from every other cause of a pale streaked leaf.
You see the silvery streaks long before the insect. The black fecal specks are what separate thrips from every other cause of a pale streaked leaf.
Find your pattern
Pick up an affected leaf and hold it against the light. The patterns below point at completely different causes, and telling them apart is most of the diagnosis.
The causes, in the order they actually occur
Ranked by how often each one turns out to be the answer, rather than by how interesting it is. Open a cause for the fix.
1 They rasp the cell surface and drink this is the signature
That is why the damage is silvery streaking rather than holes: emptied cells reflect light differently.
2 They hide where spray cannot reach
Feeding happens inside buds and growing tips, so a single application misses most of the population.
3 Part of the life cycle is in the soil
Foliar treatment never reaches it, which is why suppression is realistic and elimination usually is not.
4 Dry air suits them
As with spider mites, indoor infestations often sit on top of very dry room air.
5 Numbers rise before damage shows
By the time streaking is obvious the population is high, which is what makes sticky card monitoring worth the trouble.
What not to do first
Reflexes that make the problem worse, all of them common and all of them understandable.
You will see the damage long before you see the insect
Thrips are about a sixteenth of an inch long, slender and cylindrical, with narrow wings folded flat along the back, and they range from yellowish through brown to black. At that size they are a moving speck, and most people never identify them directly.
What you see instead is the feeding scar. Thrips do not chew holes; they rasp the surface of the cell and drink what comes out, so the emptied cells reflect light differently. That produces the signature: irregular silvery streaks, flecks or splotches on the leaf, as though someone dragged a dry brush across it.
The confirming detail is the black specks. Small dark fecal spots scattered across the silvered area are what separate thrips from every other cause of a pale streaked leaf, and they are visible with a hand lens or good light.
Telling it apart from the things it resembles
Several problems produce a pale, stippled or streaked leaf, and they call for completely different responses.
- Silvery streaks plus black specks
Thrips. The specks are the diagnostic half.
- Fine stippling with webbing, worse in dry air
Spider mites. No black specks, and the undersides carry fine silk.
- Pale winding tunnels inside the leaf
Leaf miner larvae, working between the leaf surfaces.
- Uniform pale mottling with distorted growth and no insects
Virus, which thrips can cause but do not have to. See below.
- Bleached patches on the sunny side
Sun scorch, common after a plant is moved into stronger light.
Where the damage is on flowers rather than leaves, thrips rise up the suspect list quickly. Feeding inside a developing bud collapses cells before the flower opens, so the bloom emerges streaked, flecked or misshapen, and the cause is invisible by then.
The same comparison, side by side
| What you see | Black specks? | Webbing? | Cause |
|---|---|---|---|
| Silvery streaks, flecks or splotches, as if brushed with a dry brush | Yes | No | Thrips. The specks are the diagnostic half |
| Fine even stippling, worse in dry air | No | Yes, fine silk on the undersides | Spider mites |
| Pale winding tunnels inside the leaf | No | No | Leaf miner larvae |
| Uniform pale mottling with distorted growth, no insect present | No | No | Virus. Thrips can cause it and are not always the source |
| Bleached patches on the side facing the light | No | No | Sun scorch after a move to stronger light |
| Flowers opening streaked or misshapen | Often, deep in the bud | No | Thrips feeding inside the bud before it opened |
The reason thrips matter more than the damage suggests
Direct feeding is usually cosmetic on an established plant. The serious problem is that thrips act as vectors for tospoviruses, specifically impatiens necrotic spot virus and tomato spotted wilt virus.
That changes the calculation. Those viruses are not treatable, they affect a wide range of ornamentals and vegetables, and an infected plant has to be removed to stop it becoming a source. So on a plant that matters, thrips are worth acting on earlier than the leaf damage alone would justify.
It also means a plant showing mottling and distortion after a thrips infestation may not be recovering at all. It may be infected, and no treatment addresses that.
Monitoring, which is unusually useful here
Thrips populations rise fast and hide in buds and growing tips, so by the time damage is obvious the numbers are already high. Sticky cards solve that.
Yellow or blue sticky cards placed at crop height are described as excellent for monitoring thrips, with blue particularly effective. Put a card near susceptible plants and check it weekly. It will not control anything, and it tells you whether numbers are rising or falling, which judging by eye does not.
Tapping a flower or shoot over a sheet of white paper is the free version: the thrips fall out and become visible against the white.
What to do, in order
- Remove the worst affected growth
Thrips concentrate in buds and shoot tips. Cutting off heavily infested tips removes a large share of the population in one action.
- Raise the humidity indoors
Thrips, like spider mites, do better in dry air. This is often the underlying condition on a houseplant.
- Wash the plant
A firm spray of water dislodges a surprising number, particularly on smooth-leaved plants, and costs nothing.
- Use insecticidal soap if numbers justify it
Small soft-bodied insects such as thrips are among the most susceptible to insecticidal soap. Two things about it matter: it is a contact insecticide, so it only works where the spray actually lands, and once dry it has no effect at all.
- Repeat, because of where they hide
A single application misses everything inside a closed bud. Repeat treatments a few days apart are what reduce a population rather than a generation.
Where a stronger product is warranted, rotating between different insecticide classes is standard practice with this pest, because thrips develop resistance quickly. The label on the container you own is the authority on what may be used on which plant.
What eats thrips
This matters more on thrips than on most pests, for the reason the next section explains: they develop resistance quickly, so a garden where the predators are working is doing something a spray program cannot sustain.
The list of natural enemies is longer than people expect.
- Minute pirate bugs, Orius species, are the ones worth knowing by name. They are among the most effective predators of thrips, they are mass-produced commercially for exactly this purpose, and they turn up on their own in gardens that have not been sprayed.
- Predatory mites, which hunt thrips larvae in the places sprays do not reach.
- Green and brown lacewings, whose larvae are general predators of soft-bodied insects.
- Predatory thrips, which prey on the plant-feeding ones. Not every thrips on a leaf is a pest.
- Parasitic wasps, small enough to go unnoticed entirely.
- Spiders. Yes, spiders eat thrips, and they are listed among the natural enemies of species such as redbanded and melon thrips. They are generalists rather than specialists, so they take thrips as part of a mixed diet rather than seeking them out, which means a spider population is a sign of a functioning garden rather than a thrips solution on its own.
The practical point is that none of these is something you buy for a garden bed; they are something you keep. Conserving them comes down to a short list.
- Avoid broad-spectrum, persistent insecticides for any pest on the plant, not just for thrips. A spray applied for something else removes the predators that were holding the thrips down, and thrips rebound faster than their enemies do.
- Grow a diversity of plant species. Generalist predators need alternative prey and nectar through the parts of the season when the pest is absent.
- Keep dust down. Dust favors thrips and mites and hinders their predators. Rinsing dusty foliage on small plants is a real measure rather than a cosmetic one, particularly on plants beside a path or a drive.
Bought releases are a different matter and belong in an enclosed space. Orius and predatory mites are released routinely in greenhouses and high tunnels, where the population stays where it is put. Released into an open garden they disperse, and the money goes with them.
The life cycle, which explains the rest
Most of what makes this pest difficult follows from four facts about how it reproduces, and none of them is visible on the plant.
- The eggs are inside the plant. A female cuts into plant tissue and inserts her eggs into it, so no spray reaches them. She may lay anywhere from a couple of dozen to a couple of hundred.
- Part of the population is not on the plant at all. Juveniles pupate on leaves, in the soil, or in leaf litter. A thorough foliar treatment misses whatever is pupating in the ground beneath it, and those emerge as adults days later.
- The generation time collapses in heat. Egg to adult takes about a month at 60°F and two weeks or less at 85°F. Adults then live a month or more. Generations overlap, so every stage is present at once through the season.
- Many species reproduce without mating. One surviving female is a population.
Put together, that is why a single treatment appears to work and then fails: it kills the exposed adults and larvae, leaves the eggs sealed in the tissue and the pupae in the soil, and both classes emerge into a plant that now has fewer predators on it. Repeat applications are not a sign of a weak product; they are what the life cycle requires.
It also explains the sanitation advice. Overwintering happens as adults, pupae or eggs depending on species, in soil, foliage, plant debris and under bark. Clearing debris around affected plants in autumn removes overwintering sites that no spring spray will reach.
Why they are hard to eliminate
Three things work against you. They are small enough to be missed on inspection, they feed inside buds where spray cannot reach, and part of the life cycle happens in the soil or growing medium, out of reach of anything applied to foliage.
That is why the realistic goal is suppression rather than elimination, and why removing infested growth does more than most spraying. On an outdoor ornamental with cosmetic damage late in the season, the correct response is often nothing at all.
Frequently asked questions
- What do thrips look like?
- About a sixteenth of an inch, slender and cylindrical, with narrow wings folded along the back, in yellow, brown or black. They are easier to find by tapping a flower over white paper than by searching the leaf.
- How do I know it is thrips and not spider mites?
- The black specks. Thrips leave small dark fecal spots across the silvered area; spider mites leave fine webbing and no specks. Both are worse in dry air, which is why they get confused.
- Are thrips dangerous to the plant?
- The feeding is usually cosmetic. The real risk is that they transmit tospoviruses, impatiens necrotic spot virus and tomato spotted wilt virus, which cannot be treated and mean removing the plant. That is why they are worth acting on earlier than the leaf damage suggests.
- Does insecticidal soap work on them?
- Yes, they are among the most susceptible pests to it, with two caveats: it only works where the spray lands, and it has no effect once dry. Repeat applications a few days apart are necessary because thrips sit inside buds.
- Why do they keep coming back?
- Part of the life cycle takes place in the soil or growing medium, and the feeding stages hide inside closed buds, so no foliar treatment reaches the whole population. Suppression is realistic; elimination usually is not.
Entries where this comes up most
Plants whose own record carries a note about this, because for them it means something particular.
Next to this one
Most people arriving here have a second condition as well. These are the common pairings.
Questions
Both work for monitoring at crop height and blue is described as particularly effective for thrips. Either tells you whether numbers are rising or falling, which the eye cannot judge.
Tap a flower or shoot over a sheet of white paper. They fall out and are visible against the white, which is far easier than searching the leaf surface.
On the affected leaves and flowers, yes; cells that have collapsed do not refill. New growth after the population is reduced comes in clean, so recovery shows in the new leaves rather than the old.
The same species move between both, and indoor plants are often worse because the air is drier and there are no predators. Outdoors, late-season damage on an ornamental is usually cosmetic and needs no action.
How this page is compiled
- Everything here is drawn from horticultural sources rather than from other gardening sites.
- Where a plant is named, it links to its own record, which carries the fields this page depends on.
- A claim we cannot source is left out rather than softened into a maybe.
Gardnicks editorial desk · reviewed 2026-08-17