A really good OMRI spider mite killer that kills the adults, the larvae, and the eggs with one application is a product called Organocide and runs like 15 to 18 bucks for a bottle of concentrate that will make 16 gallons. It is simply fish oil, sesame oil, and rosemary oil and it kills them fuckers dead at all stages of development as I stated earlier, kills the adults, larvae, and the eggs. The only mites left alive after an application are those you did not hit with the drench. Go back a week later and drench again. No fracking mites.
Mighty Wash is good but expensive and only kills the adults. I use that in the last three weeks of bloom only and when or if if I get an out break at that stage. I use the organicide once a week and no mites. here's a pic of the product below. You can buy a bottle of concentrate for as cheap as 15 bucks on Amazon. Now the draw back is that your veg room or bloom room will smell like a New Orleans cannery for 4 to 8 hours afterwards and then fade. I personally don't care about a little fish smell here and there if the mites are all dead without using a pyritheum or IMAD if there is large infestation. I have used this Organicide on a plant covered in mites and web outside and drenched the outdoor plant with this and the next day 99 percent of all them little bloody buggering buggers were dead Oxanaca. I would suggest adding this Organocide to your arsenal of mite preventatives and killers bro.
Best to you always from the Ol' Mile High Bluzboy
