Flower thrips are tiny, slender insects roughly 1 mm (about 1/25 of an inch) long that feed on blossoms, foliage, and fruit across a wide range of plants. Several species go by this common name, but the two most frequently encountered are the eastern flower thrips (Frankliniella tritici) and the western flower thrips (Frankliniella occidentalis). Both cause similar damage: silvery streaks on petals, distorted buds, scarred fruit, and in some cases, the spread of plant viruses. Their small size makes them easy to overlook until the damage is already visible.
How to Identify Flower Thrips
Adult flower thrips are elongate, yellow to light brown, and have distinctive fringed wings that look feathery under magnification. At only about 1 mm long, they’re barely visible to the naked eye, but you can spot them by gently shaking a flower over a white sheet of paper and watching for tiny, darting specks. Their larvae are even smaller (around 0.5 mm), wingless, and pale yellow. They look like miniature versions of the adults.
The life cycle moves through egg, two larval stages, a prepupa, a pupa, and then the adult. Eggs are kidney-shaped and only about 0.4 mm long, inserted directly into plant tissue, which makes them invisible from the outside. Pupae develop in the soil or leaf litter rather than on the plant, so you won’t find every life stage in the same place. Warmer temperatures speed up the entire cycle, meaning populations can explode quickly in summer or inside greenhouses.
What Flower Thrips Damage Looks Like
Thrips feed by rasping the surface of plant cells and sucking up the contents. This creates silvery or bronze streaks on leaves and petals, often accompanied by tiny black dots of excrement. On flowers, the damage shows up as brown-edged petals, distorted blooms, and buds that fail to open properly. Pre-bloom feeding can deform blossoms and leaves enough to reduce fruit set or weaken developing fruit, making it more vulnerable to frost and temperature stress.
On fruit crops, the damage depends on the type of plant. Stone fruits (peaches, cherries, plums) tend to suffer more than apples, developing scars that resemble frost injury. On apples, feeding damage is usually only one cell deep on the skin, but early-season injury leads to russeting by harvest. The most distinctive apple damage comes from egg-laying: thrips puncture the fruit to insert eggs, creating a condition called “pansy spot,” a whitish discolored area shaped like pansy petals surrounding a small scar. On dark red apple varieties the color eventually covers the spot, but yellow, pink, and green varieties stay discolored through harvest.
Virus Transmission
Beyond cosmetic damage, flower thrips carry plant viruses that can devastate crops. The most significant is tomato spotted wilt virus (TSWV), the most widespread plant-infecting RNA virus in the world. It affects more than 1,000 crop species, including tomatoes and peppers, causing chlorotic patches, concentric rings, necrotic spots, leaf puckering, and mosaic patterns. Western flower thrips are the most efficient carriers due to their high reproductive rate and habit of feeding on many different plant species. The virus is picked up during the larval stage and transmitted for the rest of the insect’s life, so controlling thrips early is critical in crops vulnerable to TSWV.
Monitoring With Sticky Traps
Because thrips are so small, sticky card traps are the most practical way to detect them before damage becomes obvious. Blue sticky cards are the most attractive to western flower thrips specifically, but yellow cards are generally recommended because they catch a broader range of pest species and make it easier to identify and count insects against the brighter background.
Place yellow sticky cards vertically in the crop canopy so the lower third sits below the top of the foliage and the upper two-thirds extends above it. Raise the traps as plants grow to maintain this positioning. In greenhouses with multiple cultivars, concentrate traps among the most susceptible varieties. For large, uniform greenhouses, at least 8 traps per 100,000 square feet provides adequate coverage. In smaller setups like a greenhouse rose operation, three traps per cultivar is a reasonable starting point. Check traps weekly and record counts so you can catch population spikes early.
Cultural and Physical Controls
Exclusion and sanitation are the first lines of defense. In greenhouses, fine mesh screening over vents can physically block thrips from entering. Remove and dispose of heavily infested plants or flowers promptly, because thrips will migrate from damaged plants to healthy ones nearby. Choosing resistant cultivars where they exist also helps reduce the problem at its source.
Reflective mulch (silver or aluminum-colored plastic laid around the base of plants) can disorient thrips and reduce the number that land on your crops. Keeping weeds and plant debris cleared from around growing areas removes alternative hosts and pupation sites. These steps won’t eliminate thrips entirely, but they lower the baseline population enough that other control methods become more effective.
Biological Control
Several natural enemies feed on flower thrips and can keep populations manageable, especially in greenhouse settings. Minute pirate bugs (Orius species) are among the most effective predators. They actively hunt thrips in flowers and tight plant crevices where sprays can’t reach. One important consideration: Orius species enter a dormant state when day length drops below a critical threshold. For the most commonly used species, Orius insidiosus, that threshold is between 11 and 12 hours of daylight, making it effective through most of the growing season but less reliable in late fall and winter without supplemental lighting.
Predatory mites, particularly Amblyseius cucumeris, are another widely available option. They feed on thrips larvae and work well as a preventive measure when released before populations build. Tiny parasitic wasps in several genera also attack thrips larvae internally, though these are less commonly sold commercially and play a larger role in natural outdoor suppression than in managed release programs.
Spray Options and Their Limits
Thrips are notoriously difficult to control with sprays. Their small size, mobility, tendency to hide in tight buds and leaf folds, and the fact that eggs are embedded inside plant tissue and pupae live in the soil all mean that many insects escape contact with any spray you apply. Timing, thoroughness, and product choice all matter.
Contact sprays like insecticidal soap, horticultural oil, neem oil, and pyrethrins provide temporary knockdown but only kill the thrips they physically touch. To get results, you need to thoroughly coat buds, shoot tips, and any other plant parts where thrips are feeding. Repeat applications are necessary as long as thrips and vulnerable plant tissue are both present.
Spinosad, a naturally derived insecticide produced by soil bacteria, is generally more effective than the contact options. It persists for a week or more and has translaminar activity, meaning it moves a short distance into sprayed tissue to reach thrips feeding in protected spots. Mixing horticultural oil into the spray can extend its persistence. Certain spinosad formulations qualify as organically acceptable, making it a strong option for organic growers. Start treatment early when thrips or their damage is first noticed on plants with a history of problems, rather than waiting for heavy infestation. By the time damage is widespread, the population is already well established and much harder to bring under control.