The broad mite (Polyphagotarsonemus latus) is a tarsonemid mite about 0.2 mm long, too small to see with the naked eye or a 10x loupe. It feeds on the youngest leaves and shoot tips. Its saliva is toxic to the plant, so even a modest population distorts growth far out of proportion to its size.
In practice
The classic picture is new growth that is twisted, narrow, shiny or glassy, with leaf edges curling down and tips that stall. Growers often chase it as a calcium or boron problem first. Confirming it takes a 40-60x scope or a digital microscope on a growing tip: look for clear oval adults and eggs dotted with white bumps. Broad mites travel on clones, clothing and air currents, so quarantine of incoming cuts is the main defence. Predatory mites such as Amblyseius swirskii and Neoseiulus californicus are used against them. In flower, options shrink sharply; check what is registered for cannabis locally.
Don't confuse with
- Hemp russet mite: an eriophyid mite that bronzes and curls leaves upward, usually starting lower on the plant.
- Calcium or boron deficiency: no mites under magnification, and the damage tracks root-zone conditions.
- Heat or light stress: improves when the stress is removed.
The zone of dividing cells at the very tip of a shoot (or root) that produces new leaves, nodes and stem; removing it is what topping does.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.Mites, mostly of the family Phytoseiidae, released as biological control to eat pest mites, thrips larvae, whitefly eggs or fungus gnat larvae.A warmth-loving generalist predatory mite that eats thrips larvae, whitefly eggs and nymphs and broad mites, and can persist on pollen.A generalist-leaning predatory mite that eats spider mites and broad mites, survives on low prey or pollen, and tolerates warmer, drier rooms than Phytoseiulus.Aculops cannabicola, a microscopic eriophyid mite specific to cannabis that causes upward leaf curl, bronzing and dull, greasy-looking trichomes.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.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.Phytonemus pallidus, a tarsonemid mite related to the broad mite that distorts new growth on many ornamentals; rarely reported on cannabis and often confused with broad mite.Holding incoming plants, clones or seeds apart from the main grow, under observation and sometimes treatment, until they are shown to be free of pests and disease.
