Thrips are tiny, slender insects of the order Thysanoptera with fringed wings. On cannabis the main indoor species is western flower thrips (Frankliniella occidentalis); onion thrips (Thrips tabaci) also occur. They scrape the leaf surface and suck the leaking contents, leaving silvery or bronze patches speckled with black droppings. The word is both singular and plural.
In practice
Thrips run a split life cycle. Eggs go inside the leaf, larvae feed on foliage, and most species drop to the growing medium to pupate. That is why good programmes hit two places: predatory mites such as Neoseiulus cucumeris or Amblyseius swirskii on the leaves, and soil predators such as Stratiolaelaps scimitus or nematodes in the medium. Blue or yellow sticky traps at canopy height show trends; a jump from a few per card per week to dozens means act now. Western flower thrips resist many insecticide classes, so rotation by mode of action matters. Check what is registered for cannabis locally.
Don't confuse with
- Spider mite damage: fine pale stippling, no streaks or black specks.
- Leafminer trails: winding tunnels inside the leaf, not surface scars.
- Fungus gnats on traps: dark flies with long legs, not slim straw-coloured insects.
Mites, mostly of the family Phytoseiidae, released as biological control to eat pest mites, thrips larvae, whitefly eggs or fungus gnat larvae.A predatory mite that eats first-stage thrips larvae and some broad and cyclamen mites; tolerant of cooler rooms and widely used in sachets as a preventive.A warmth-loving generalist predatory mite that eats thrips larvae, whitefly eggs and nymphs and broad mites, and can persist on pollen.A soil-dwelling predatory mite, formerly sold as Hypoaspis miles, that hunts fungus gnat larvae, thrips pupae and other small arthropods in the growing medium.An entomopathogenic nematode applied as a soil drench whose infective juveniles enter fungus gnat larvae and thrips pupae and kill them with symbiotic bacteria.A coloured card coated in non-drying glue that catches flying insects, used mainly to monitor pest trends: yellow for gnats, whiteflies and aphids, blue for thrips.Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.Minute pirate bugs of the genus Orius, such as Orius insidiosus, that hunt adult and larval thrips plus mites and aphids; some strains pause breeding under short days.
