Spider Mites
Definition: Spider mites are tiny arachnids, barely visible at about 1/50 of an inch long, that pierce cannabis leaf cells and suck out their contents. They leave pale speckles on leaves, multiply rapidly in hot, dry conditions, and in heavy infestations wrap buds and branch tips in fine silk webbing.
How Spider Mites works
The two-spotted spider mite is the species most indoor cannabis growers meet. In warm conditions, a generation can go from egg to egg-laying adult in about a week, so a few mites can become thousands within 2 to 3 weeks.
Early signs
- Tiny white or yellow dots (stippling) on the upper side of leaves.
- Moving specks on leaf undersides, visible with a 30x to 60x loupe.
- Leaves that look dusty, dull, or bronzed.
- Fine webbing between leaves and stems, a sign the population is already large.
Conditions they love
Hot, dry air helps mites breed faster. Grows running low relative humidity and high temperatures in late flower are especially vulnerable.
Control in veg
- Spray leaf undersides thoroughly with water to knock mites off.
- Use insecticidal soap or other products labeled for mites, following the label and your state’s rules on cannabis inputs.
- Release predatory mites, such as Phytoseiulus persimilis for active outbreaks or Neoseiulus californicus for prevention.
Control in flower
Avoid spraying buds. Predatory mites are the main tool once flowers form, combined with removing the worst-infested leaves.
Prevention
Mites usually arrive on clones, houseplants, pets, or clothing after you’ve been outdoors. Quarantine new plants, inspect weekly with a loupe, and clean the space thoroughly between runs. Their damage can look similar to thrips, so confirm what you’re seeing before treating.