Common Cannabis Pests: Fungus Gnats, Spider Mites, and Thrips

You'll meet these eventually. Catching them early is the entire game — a pest you spot at five individuals is a sticky trap; at five hundred it's a war. FUNGUS GNATS - ID: tiny black flies hovering over the soil, especially after watering. Larvae in the top inch of wet medium are what actually eat roots. - Cause: chronically wet topsoil. They're a symptom of overwatering as much as a pest. - Fix: let the top inch or two of medium dry between waterings — this alone breaks their life cycle. Yellow sticky cards catch adults. BTi (sold as Mosquito Bits/Dunks, watered in) kills larvae biologically and is safe through the whole grow. SPIDER MITES - ID: fine yellow-white speckling on leaf tops, then tiny webbing under leaves and between buds. Tap a leaf over white paper and look for moving dots. - Cause: hot, dry air and hitchhiking on clothes/pets/tools. - Fix: they hate moisture — lower temps and raise humidity while treating. In veg: insecticidal soap or neem (spray leaf UNDERSIDES, lights off or about to be). Predatory mites (Phytoseiulus persimilis) are the clean nuclear option for a sealed tent. - In flower, do NOT spray buds with anything — soap, neem, and oils all ruin them. Predators and environment only, or cull. THRIPS - ID: silver/bronze streaks and shiny specks on leaves, with tiny slender yellow-white bugs visible on close inspection. - Fix: sticky cards, insecticidal soap in veg, spinosad is effective but keep it out of flower — same rule as everything else: nothing sprayed on buds past early flower. Ever. PREVENTION — THE PART THAT MATTERS - Sticky cards up from day one, even with no pests — they're your early-warning system. - Quarantine anything that comes from outside: clones especially (hold 1–2 weeks and inspect daily). - Keep the floor clean, intake filtered if possible, and don't walk into the tent straight from the garden. - Inspect leaf undersides weekly with a loupe. Pests hide where nobody looks.