A caterpillar is the larva of a moth or butterfly (order Lepidoptera). Several groups attack cannabis: leaf chewers such as loopers and armyworms, stem borers such as the European corn borer (Ostrinia nubilalis) and the hemp borer (Grapholita delineata), and bud feeders such as the corn earworm (Helicoverpa zea). Outdoor and greenhouse crops carry most of the risk; sealed indoor rooms rarely see them.
In practice
Signs are ragged holes in leaves, wilting branch tips above a borer's entry hole, and above all frass (droppings) inside buds. Wet frass and chewed tissue give Botrytis an easy entry, so one caterpillar can rot a whole cola. Growers scout for moths at dusk, eggs on leaf surfaces and fresh frass. Bacillus thuringiensis products, which must be eaten to work, are the standard biological option and work best on young larvae before they bore into buds. Netting and pheromone traps help outdoors. Check what is registered for cannabis locally.
Don't confuse with
- Fungus gnat larvae: tiny clear maggots in the medium, not on the plant.
- Cutworms: a caterpillar group that hides in soil by day and severs seedlings at the base.
- Slug damage: holes plus slime trails, usually low on the plant.
Hemp is cannabis grown for fibre, seed or other uses and, in many laws, defined as Cannabis sativa with no more than 0.3% THC by dry weight.Helicoverpa zea, a moth caterpillar that bores into developing cannabis flowers outdoors, leaving frass that triggers bud rot; growers call it budworm.Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower.The dense, elongated cluster of flowers that forms at the end of a stem or branch; the main cola tops the leader.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.Moth caterpillars of the family Noctuidae, such as the black cutworm (Agrotis ipsilon), that hide in soil by day and chew through seedling stems at night.A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks.Systematic, regular inspection of plants, traps and roots to detect pests and disease early, identify them correctly and record numbers for decisions.
