Common Cannabis Pests and How to Beat Them

Every grower meets pests eventually — the difference between a hiccup and a disaster is finding them in week one instead of week six. Here are the usual suspects, the evidence they leave behind, and the safest ways to fight them.

Spider Mites — The Micro Menace

Evidence: tiny pale dots (stippling) on leaves, fine webbing in leaf joints, and moving specks no bigger than this full stop. They explode in hot, dry tents and can crash a plant in two weeks.

Treatment: spray undersides with insecticidal soap or a dedicated miticide labelled for edibles, repeating every 5 days to catch hatching eggs. Amblyseius predatory mites are excellent prevention. Never let a tent get hot and bone-dry — that's an invitation.

Fungus Gnats — More Than a Nuisance

Evidence: little black flies hovering over wet soil; their larvae eat root hairs, stunting young autos. A classic symptom of chronic overwatering.

Treatment: let the top 3 cm of soil dry out between waterings, cover the surface with a 1 cm layer of sand or perlite, and hang yellow sticky traps. Bacillus thuringiensis (BTI) drenches kill larvae cleanly.

Aphids — The Sap Suckers

Evidence: clusters of green, black, or grey pear-shaped insects on soft new growth, plus sticky "honeydew" and curled leaves.

Treatment: knock them off with a water spray, then follow with insecticidal soap every few days. Ladybugs and lacewings do the job outdoors for free.

Thrips — The Scrappers

Evidence: silvery scratch marks and tiny black droppings on leaves, like someone sanded the surface.

Treatment: blue sticky traps plus insecticidal soap; predatory mites (Amblyseius cucumeris) for repeat offenders.

The Golden Rules of Pest Control

1. Inspect weekly, under leaves. Buy a cheap 60x jeweller's loupe and use it.
2. Quarantine new plants — clones and gifts from friends bring hitchhikers.
3. Treat at the label rate. Doubling "to be sure" burns plants and leaves residues.
4. In flower, choose biologicals — Bacillus-based sprays, insecticidal soap early in flowering, and predators. Stop all sprays once buds are formed, and never spray open buds with anything.
5. Clean between cycles. Pests and their eggs survive on pots, trays, and tent seams.

Outdoors: Larger Problems, Larger Tools

• Deer and rabbits: fencing and raised beds.
• Caterpillars (cabbage loopers, hornworms): hand-pick at dusk, or use BT (Bacillus thuringiensis), which is safe and effective.
• Slugs: beer traps and copper tape around pots.

The best pest protection is a healthy, unstressed plant — robust autos shrug off small infestations, while struggling ones get overrun. Good airflow, sensible watering, and a morning look-over are your best defences.

Written by the Autoflower.net Editorial Team. Information on this page is educational and does not replace strain-specific breeder guidance. Laws on cannabis cultivation vary by jurisdiction — check your local rules before growing.