Short answer. Most indoor pests arrive on clones, plants, outdoor soil, pets or clothes, and are found too late. Prevent them in this order: quarantine anything new for 10–14 days, start with clean media and a clean room, hang sticky traps and scout under leaves with a loupe weekly, release predatory mites before you need them, and act at the first find, not the first damage. Don't spray buds in flower. Clones can also carry hop latent viroid, so grow from seed or test the cut.
Prevention is the whole game for a beginner. Once spider mites or broad mites are established in a flowering tent, there are few good options left. This guide is the routine; the deep articles cover each pest. The approach is IPM: prevention, monitoring and the least-harmful control that works [4].
What do you need for pest prevention?
Pest prevention needs cheap, generic kit used consistently:
- [ ] Yellow sticky traps (and a blue one if you suspect thrips), 1–2 per tent at pot level and canopy level
- [ ] A 30–60x jeweller's loupe or phone macro lens
- [ ] A separate quarantine space: a second small tent, a spare room or a shelf far from the grow
- [ ] Fresh bagged potting mix or coco (never garden soil indoors)
- [ ] A spray bottle, mild detergent and a diluted disinfectant for cleaning between runs (sanitation)
- [ ] Dedicated grow clothes or an apron, and disposable gloves
- [ ] Intake filter material (a fine mesh or pre-filter) on any passive or active intake
- [ ] Optional: sachets or loose predatory mites from a biological supplier (biological control)
How do you prevent pests, step by step?
- Clean before you start. Empty the tent, wash walls and floor with detergent, then disinfect and let it dry. Wash pots and trays. Throw out old, used media.
- Start from seed if you can. Seeds carry far fewer pests and pathogens than clones. If you take a clone, follow step 3 without exception.
- Quarantine every new plant for 10–14 days. Keep it in a separate space, inspect it every 2–3 days with the loupe, under every leaf layer, and hang a sticky trap next to it. Many pests need one or two life cycles to show; spider mites can complete one in about a week in warm rooms [1].
- Ask about, or pay for, an HLVd test on any clone. Hop latent viroid has no cure, can hide without symptoms and spreads on tools and hands [8][9].
- Close the doors pests use. Keep the tent zipped. Filter intakes. Keep houseplants, cut flowers and pets out of the grow room. Don't go from the garden, or a friend's grow, straight into yours; change clothes first.
- Hang traps on day one. One at pot level for fungus gnats and shore flies, one at canopy level for thrips, whiteflies and winged aphids. Replace them monthly or when 30–50 % covered [2][4].
- Scout weekly, plant by plant. Turn over 5–10 leaves from the bottom, middle and top. Look for pale stippling, webbing, eggs, moving dots, silvery scars with black specks, curled or bronzed new growth. Count insects on the traps and log the counts.
- Release predators preventively. In veg, a generalist predatory mite such as Neoseiulus californicus, Neoseiulus cucumeris or Amblyseius swirskii every 2–4 weeks, and Stratiolaelaps scimitus once per pot for fungus gnat larvae and thrips pupae [5][6][7]. Predators keep working into flower, where sprays can't.
- Keep the climate out of the pest zone. Spider mites breed fastest in hot, dry rooms; keep temperature under about 28 °C (82 °F) and RH in range (climate basics) [1]. Fungus gnats need constantly wet media; let the top 2–3 cm (1 in) dry between waterings [3].
- Act at the first find. Identify the pest (see the table), remove the worst leaves into a sealed bag, add or increase predators, and in veg only, use a soap or oil treatment on the undersides of leaves if needed. Log what you did and re-scout in 3–4 days.
- No sprays on buds. From about week 2–3 after the flip, nothing wet goes on flowers. Residues stay in the resin, and wet buds rot.
- Clean out completely between runs, before the next plants arrive.
Which pests should a beginner know, and how do you spot them?
Learn these eight; between them they cover nearly every indoor home-grow problem.
| Pest | Telltale sign | Where to look | First response | Deep article |
|---|---|---|---|---|
| Spider mites | Pale pin-prick stippling on leaf tops, fine webbing | Leaf undersides, mid-canopy | Predatory mites, cool and raise RH, remove leaves | Spider mites |
| Broad and russet mites | Twisted, glossy, bronzed new growth; mites invisible without high magnification | Growing tips | Act at once; often from clones | Broad and russet mites |
| Thrips | Silvery scars with black specks | Leaf tops and undersides, traps | Cucumeris or swirskii, blue traps | Thrips |
| Fungus gnats | Small dark flies over wet medium | Pot surface, low traps | Let the medium dry, Bti, S. feltiae, soil mites | Fungus gnats |
| Root aphids | Slow, yellowing plants; white waxy specks on roots | Root ball, drainage holes | Isolate; often from soil or clones | Root aphids |
| Aphids | Clusters on stems and new growth, sticky honeydew | New growth | Wipe, beneficials, soap in veg | Aphids |
| Whiteflies | Tiny white moths flying up when disturbed | Leaf undersides, traps | Yellow traps, predators | Whiteflies |
| Caterpillars | Chewed leaves, droppings, rotting buds | Inside buds (mainly outdoors) | Hand pick; Bt in veg | Caterpillars |
When should you act?
Act on the first confirmed find for pests that breed in days, and on a rising trend for nuisance pests. Commercial greenhouse action thresholds are set for big crops [4]; a home tent with one to four plants has no margin, so the GenetixBay home thresholds are strict:
| Find | Action threshold (home grow) |
|---|---|
| Spider mites, broad or russet mites, root aphids | One confirmed colony or one damaged growing tip: act today |
| Thrips, whiteflies, aphids | Any on a plant, or trap counts rising week on week: add predators, remove infested leaves |
| Fungus gnats | More than about 5–10 a week on a pot-level trap: dry the medium out, add Bti or nematodes |
| Anything in flower | No sprays on buds; predators, traps, climate and leaf removal only |
How will you know prevention is working?
You'll know prevention is working when your weekly scouting is dull:
- Sticky trap counts stay at zero to a handful per week, with no rising trend.
- Leaf undersides are clean under the loupe: no stippling, eggs or webbing.
- New growth is flat and normally coloured, not twisted or glossy.
- Predatory mites, if released, are visible as fast-moving tan or pear-shaped mites on leaf undersides.
- Quarantined plants come out clean after 10–14 days, and nothing appears in the main tent 2–3 weeks after they join it.
- You reach harvest without having sprayed anything in flower.
What mistakes do beginners make with pests?
- Bringing in an untested clone straight into the main tent. Quarantine, inspect, test for HLVd.
- Using garden soil or reused, untreated media indoors.
- Spraying in flower. It damages trichomes, leaves residue and invites bud rot.
- Waiting for damage before scouting. By the time leaves look speckled from a step back, the colony is large.
- Constantly wet pots, which breed fungus gnats.
- Hot, dry tents, which breed spider mites.
- Mixing predators with broad-spectrum sprays, which kills the predators first.
- Going from the garden or a friend's grow into your tent in the same clothes.
- One-off treatments. Most pests need follow-ups timed to their life cycle, usually every 3–7 days for 2–3 rounds.
Evidence
- Quarantine, sanitation and scouting as the foundation of IPM: Established extension practice [4][9].
- Spider mite life cycle speeding up in hot, dry conditions: Established [1].
- Predatory mites for spider mites, thrips and fungus gnats: Established in greenhouse crops [5][6][7].
- Fungus gnats breeding in wet media: Established [3].
- HLVd spread on clones and tools: Established [8][9]. Russet mites arriving on plant material: Supported [10].
- Home-grow action thresholds: Grower practice (house).
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.Mites, mostly of the family Phytoseiidae, released as biological control to eat pest mites, thrips larvae, whitefly eggs or fungus gnat larvae.Pest and disease prevention by changing how the crop is grown, such as humidity, airflow, spacing, watering and cultivar choice, so pests and pathogens struggle to establish.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.Slender insects about 1-2 mm long, chiefly western flower thrips (Frankliniella occidentalis), that rasp leaf surfaces, leaving silvery streaks dotted with black frass.The canopy is the top layer of foliage and buds across a grow, the surface that intercepts most of the light and where yield is mostly made.HLVd, a small infectious RNA that spreads through sap and tools, causing stunting, brittle stems, small loose buds and reduced resin in cannabis; called dudding.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew.A pattern of many tiny pale dots on leaves where a sucking pest such as a spider mite has emptied individual cells; the first visible sign of a mite infestation.Relative humidity is the water vapour in air as a percentage of what it could hold at that temperature, so the same RH dries plants differently at different temperatures.The pest or disease level, set in advance, at which a grower takes a specific control action because waiting longer would cost more than acting.Aculops cannabicola, a microscopic eriophyid mite specific to cannabis that causes upward leaf curl, bronzing and dull, greasy-looking trichomes.Aphids that colonise roots and the crown below the medium surface, on cannabis chiefly the rice root aphid (Rhopalosiphum rufiabdominale), causing slow, unexplained decline.Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.Integrated pest management: preventing and controlling pests by combining monitoring, prevention, cultural, biological and, as a last resort, chemical tools against set action thresholds.
