Pests
Identification, life cycles, thresholds and IPM.
Aphids on cannabis: cannabis aphid, green peach aphid and friends
Aphids are soft-bodied sap feeders that cluster on leaf undersides and stems, shed white skins and drip sticky honeydew; they breed asexually and fast, so catch them early and use parasitoid wasps, predatory midges and lacewings, with soaps or oils only before flower.
Broad mites and hemp russet mites: the invisible ones
Broad mites (Polyphagotarsonemus latus) twist and harden new growth; hemp russet mites (Aculops cannabicola) bronze leaves and curl edges upward. Both are too small to see without 20x or more, are mistaken for nutrient problems, and are managed by clean stock, quarantine, preventive predatory mites and removal of infested plants.
Caterpillars and budworms on cannabis
Caterpillars, mainly corn earworm (Helicoverpa zea) outdoors, bore into buds, leave frass and start bud rot; scout from early flower, use pheromone traps for moth flights, exclude moths with netting, and use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight within days.
Fungus gnats: the watering problem with wings
Fungus gnats (Bradysia spp.) breed in constantly wet, organic-rich media; adults are a nuisance but larvae chew roots of seedlings and clones and can open the door to Pythium and Fusarium. Fix the watering first, then use Bti, Steinernema feltiae nematodes or soil predatory mites, and sticky cards to monitor.
Root aphids (rice root aphid) on indoor cannabis
The 'root aphid' of indoor cannabis in North America is mainly the rice root aphid (Rhopalosiphum rufiabdominale); wingless colonies feed on roots and cause slow growth, wilting and yellowing that look like nutrient or watering problems. Confirm by inspecting roots and cards, then rely on sanitation, a plant-free gap between cycles, and soil-applied biologicals.
Spider mites on cannabis: ID, lifecycle and IPM
Twospotted spider mites (Tetranychus urticae) cause pale stippling on leaf tops and webbing at heavy populations; they breed fastest in hot, dry rooms, so control rests on early scouting, cooler and more humid conditions, and predatory mites released before numbers explode, with soaps or oils only before flower.
Thrips on cannabis: silver scars, black specks and how to break the cycle
Thrips rasp leaf cells and leave silvery scars dotted with black fecal specks; because they pupate in the medium, the fix is a two-level attack: predatory mites and bugs on the foliage plus soil-dwelling predators or nematodes below, backed by blue or yellow sticky cards and clean stock.
Whiteflies on cannabis: ID and IPM
Whiteflies are tiny white moth-like sap feeders that rise in a cloud when you shake a plant; nymphs sit flat under leaves and drip honeydew. Identify the species, monitor with yellow cards, and use Encarsia formosa (greenhouse whitefly) or Eretmocerus (warmer rooms, silverleaf whitefly) plus predatory mites, keeping sprays out of flower.
