Bti is Bacillus thuringiensis subspecies israelensis, a strain whose crystal toxins are active against the larvae of certain flies: mosquitoes, black flies and fungus gnats. Larvae must eat the bacterium for it to work. It has no effect on adult flies, caterpillars, beetles, mites or plants.
In practice
Growers drench the medium with a Bti solution, or soak granules in water and use the liquid, to cut fungus gnat larvae in the top few centimetres of soil or coco. Results show as fewer adults on sticky traps one to two weeks later, since existing adults are untouched. It breaks down within days, so repeated drenches at roughly weekly intervals during heavy pressure are typicalbeing reviewed. It pairs well with drying the medium surface and with nematodes or soil predatory mites. Check what is registered for cannabis locally.
Don't confuse with
- Btk: the caterpillar strain, sprayed on foliage.
- Steinernema feltiae: living nematodes, not a bacterial toxin.
- Hydrogen peroxide drenches: oxidisers that also harm beneficial root life.
A soil bacterium whose crystal proteins kill caterpillars after they eat treated leaves; subspecies kurstaki and aizawai are the strains used against budworms.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.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.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.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.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 soil-dwelling predatory mite, formerly sold as Hypoaspis miles, that hunts fungus gnat larvae, thrips pupae and other small arthropods in the growing medium.Hydrogen peroxide (H₂O₂) is an oxidising sanitiser used to clean hydroponic equipment and reservoirs; it breaks down quickly into water and oxygen and kills beneficial microbes too.Using living natural enemies, such as predators, parasitoids, nematodes and microbes, to suppress pests and diseases instead of, or before, chemical sprays.
