The groups within 3 weeks of harvest, add wind, drop temps, and vacuum the colas daily with a hand held dustbuster where you see webs. Really. You can attract mites to the tops of colas by putting a desk lamp right down close to one. They love the heat and dry air, and will congregate on the highest, warmest spots on your plants.
Other plants may be sprayed with pyrethrin. Or bomb the room twice with a product like Doktor Doom, spacing the treatments 2 days apart.