You recognise thrips by the damage before you see the insect: silvering of the leaf tissue, dark specks of frass, and on young fruit a ring of scarring around the calyx that stays there all season. You hold them down by combining sticky traps so you know when they arrive, rotation of modes of action because resistance builds fast, and ground cover that keeps predatory mites on site. A spray on its own no longer does the job, and there is a precise reason why.
New species changed the problem
For years thrips were a local, predictable matter. Then the invasive species arrived: Scirtothrips aurantii has moved into the citrus of Valencia and Murcia, and Spain authorised spinosad on citrus, persimmon and pomegranate precisely because resistance builds quickly and another mode of action was needed in the rotation.
This matters wherever you grow. Invasive thrips travel with planting material and on the wind, and the range widens season by season. Anyone building a defence today around a single active substance is building it on a photograph that is already out of date.
Identify the species, because it changes the defence
| Species | Where you find it | The sign that gives it away |
|---|---|---|
| Frankliniella occidentalis | vegetables, strawberry, ornamentals, glasshouse | polyphagous, transmits virus, highly resistant |
| Thrips tabaci | onion, leek, brassicas, tobacco | extensive silvering on leaves, large colonies |
| Scirtothrips spp. | citrus, persimmon, pomegranate | ring of scarring around the calyx of young fruit |
| Heliothrips haemorrhoidalis | ornamentals, avocado, glasshouse | very obvious black specks of frass |
The practical way to see them: tap a flower or a young shoot over a sheet of white paper. They are one to two millimetres long, they move immediately, and to the naked eye they look like little dashes running about. On leaves they sit almost always on the underside.
The damage: it counts more on the fruit than on the leaf
Thrips do not chew. They rupture cells and empty the contents. The emptied tissue fills with air and reflects light, and that is what you see as silvering.
- On leaves: silvering, distortion and, under heavy pressure, early leaf fall.
- On young citrus fruit: superficial scars that grow with the fruit. Sound inside, unsaleable outside.
- On flowers: abortion and uneven set.
- Indirectly, and often worst of all: Frankliniella occidentalis transmits tospoviruses. There the damage is not the feeding, it is what the insect brings with it.
The critical window is almost always between petal fall and small fruit. The scars made in those days are the ones you meet again in the packhouse.
Why a spray alone stopped working
Three reasons, and they have to be held together:
- The cycle is very short. In warm weather a generation closes in two weeks. A handful of generations under the same molecule is enough to select the resistant individuals.
- The stages hide. Part of the cycle happens in the soil and inside closed flowers. No spray reaches there, so every treatment hits only part of the population.
- There is more than one species. Different sensitivities to the same product, on the same plant.
Hence the only strategy that holds over time:
- Sticky traps, blue or yellow, checked on a fixed schedule. A single count says nothing; the curve says everything.
- Rotate modes of action, not trade names. Two different products with the same mode of action are, as far as resistance is concerned, the same product.
- Intervene in the right window, on the first mobile stages, not once the fruit is already scarred.
- Predatory mites and service vegetation in the alleys: that is the guard that keeps working between one treatment and the next.
- Netting on the sides where entry is from the field margins.
And one warning that saves money: a broad-spectrum insecticide removes the predators along with the thrips, and the rebound afterwards is worse than the original attack.
Where reading the plant comes in
A sensor in the trunk does not count thrips. Traps and flower counts do that.
What sap flow data adds is the context that turns that damage into a serious loss. A plant under water stress at fruit set sheds part of its crop by itself, and on what is left every scar weighs twice as much at grading. Anyone who works a block knows it: the bad thrips years are almost always the years the irrigation went wrong too. The plant says so first — sap flow drops days before the canopy shows anything.
The Plantvoice sensor reads sap flow and sap salinity inside the trunk continuously and turns those numbers into one instruction: irrigate now, or wait. On orchards using it, water use has fallen by up to 40% while holding quality. See detecting stress before the symptoms appear and how the sap flow sensor works.
Frequently asked questions
How do I know if I have thrips? By the silvering of the tissue with dark specks of frass, and on young citrus fruit by the ring of scarring around the calyx. To see the insect, tap a flower or a shoot over white paper: they are one to two millimetres long and move at once.
When do thrips do the most damage? Between petal fall and small fruit. The feeding of those days becomes scarring that grows with the fruit and downgrades it at harvest, even though the flesh is sound.
Why do thrips sprays work less and less? Because the cycle closes in two weeks in warm weather, because part of the life cycle sits in the soil and inside closed flowers where no spray reaches, and because species with different sensitivities live on the same plant. Rotating modes of action is the only answer that holds.
Do thrips spread viruses? Yes. Frankliniella occidentalis is the best known vector, and in that case the real damage is not the feeding but the virus it introduces. That is why the tolerance threshold on vegetables and ornamentals is far lower.
Do predatory mites work against thrips? Yes, and they are the guard that works between one treatment and the next. To keep them on site you need service vegetation in the alleys and selective products: a broad-spectrum insecticide removes them along with the thrips, and the rebound is worse.
Want to reach fruit set with plants that do not add stress to the damage? Talk to our agronomists about setting up monitoring, or ask for a Plantvoice sensor trial on your own trees.
HERO_PROMPT: Ultra-realistic editorial photograph of an extreme close-up of thrips damage on a citrus leaf, silvery scarring across the leaf surface, orchard rows blurred behind. Extreme detail on the silvered leaf tissue: visible texture, natural imperfections, true-to-life colour. Shot on a full-frame DSLR, 100mm macro lens, shallow depth of field with clean bokeh, soft natural daylight with golden-hour warmth, high dynamic range, realistic shadows and highlights, subtle analogue film grain (Kodak Portra 400), cinematic colour grading, elegant editorial composition, agricultural documentary aesthetic, photorealistic, ultra-detailed, 8K, masterpiece quality. No text, no watermark, no logo, no captions, no cartoon, no 3D render, no illustration, no AI-glossy plastic look, no oversaturated colours, no unrealistic insect anatomy, no human faces in focus, no branded products or readable labels.
