Bacillus thuringiensis (Bt) is a soil bacterium that forms crystal proteins toxic to specific insect groups. Once eaten, the crystals dissolve in the alkaline gut of the larva, bind to gut receptors and punch holes in the gut wall; the larva stops feeding within hours and dies over a few days. Subspecies kurstaki (Btk) and aizawai target caterpillars; subspecies israelensis (Bti) targets fly larvae.
In practice
Outdoor growers spray Btk or aizawai products against corn earworm, loopers and other caterpillars. Timing is everything: it must be on the leaf or flower when young larvae feed, before they bore into colas, and sunlight breaks it down within days, so repeat applications follow egg-laying. It has no contact action and does not harm bees, predatory mites or people at label rates. Whether and how late it may go on flowers depends on the product label and local rules; check what is registered for cannabis locally and respect the pre-harvest interval.
Don't confuse with
- Bti: the mosquito and fungus gnat strain, used as a soil drench.
- Bt crops: plants engineered to make Bt proteins; no such cannabis exists commercially.
- Beauveria bassiana: a fungus that infects on contact.
A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.Helicoverpa zea, a moth caterpillar that bores into developing cannabis flowers outdoors, leaving frass that triggers bud rot; growers call it budworm.The dense, elongated cluster of flowers that forms at the end of a stem or branch; the main cola tops the leader.Mites, mostly of the family Phytoseiidae, released as biological control to eat pest mites, thrips larvae, whitefly eggs or fungus gnat larvae.The minimum time, set on a pesticide label, that must pass between the last application and harvest so residues fall to permitted levels.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.An insect-killing fungus whose spores germinate on contact, penetrate the cuticle and kill soft-bodied pests such as whiteflies, thrips, aphids and root aphids.Bacillus thuringiensis subsp. israelensis, a bacterial strain whose toxins kill fly larvae, including fungus gnats, after ingestion; applied as a medium drench.The larval stage of moths and butterflies (order Lepidoptera); on cannabis, leaf-chewers, stem borers and bud-boring species whose frass seeds bud rot.Using living natural enemies, such as predators, parasitoids, nematodes and microbes, to suppress pests and diseases instead of, or before, chemical sprays.
