Spider Mites — Identification and Treatment
Spider mites are the most common cannabis pest and can devastate a crop in weeks if not caught early. Here is how to identify, treat, and prevent them.
Identifying Spider Mites
Spider mites are tiny (0.5mm) arachnids, usually red/brown or yellow/white. The first visible sign is tiny white or yellow dots on the upper surface of leaves — these are feeding punctures. Turn a leaf over and look for tiny dots moving on the underside. Advanced infestations produce fine webbing between branches and leaves. Act immediately at first sign.
Why They Spread So Fast
A single female spider mite lays 100+ eggs that hatch in 3–5 days at 27°C. A small infestation can become a full-scale invasion in 1–2 weeks in warm, dry conditions. They thrive in hot, dry environments (above 27°C, below 50% humidity) — exactly the conditions some indoor grows create during summer.
Treatment — Organic Options
First response: blast both sides of all leaves with a strong water spray to knock mites off. Follow with: neem oil spray (2ml/L + 1ml dish soap per litre), pyrethrin-based sprays, spinosad, or diatomaceous earth on soil surface. Apply every 3 days for 3 cycles to catch eggs as they hatch. Alternate treatments to prevent resistance.
Treatment — Chemical Options
For severe infestations: abamectin-based miticides are highly effective. Rotate between two different chemical classes to prevent resistance. Never spray flowers with any pesticide — this ends up in your final product. If mites reach your flowers, you have very limited options other than sacrificing affected buds.
Prevention
Keep humidity above 50% in veg. Keep temperatures below 27°C. Inspect leaf undersides with a jeweller's loupe weekly. Never introduce plants from unknown sources into your grow room. Change clothes before entering grow space if you have been outdoors. Beneficial predatory mites (Phytoseiulus persimilis) provide excellent biological control.
Quick Tips
- The window between spotting first mites and losing control is about 1 week — act immediately.
- Sticky yellow traps hung above canopy catch flying pests and give early warning of infestations.
- Spider mites hate water — a clean, humid grow environment is the best prevention.