i once used spinosad as a repellant and it worked great. Dead bug jack's brew with spinosad it was called. I also added spreader sticker solution to really make the application "stick".
Before applying, i watered my plants, and let the temperatures go up to 80-85(i believe this makes the spider mites less dormant and more active, and when they get hit with the spinosad they really absorb it). Now i shut the lights off and spray my spinosad application thoroughly, starting by working my way up with my spray bottle that can spray upside down on the undersides of all the leaves of each individiual plant, and afterward do a final top-canopy mist. now i let it sit in there for about an hour and take the plants outta there and as i take each one out, i re-mist them. now i bleach my room , every single crevice, because an egg could be hidden anywhere.
a week later i do a mild misting
always try and stop the problem all the way before flowering. I also keep the room very neat vacuuming up any dead leaves and vacuuming out the room weekly
i don't use bagged soil anymore just coco fiber and bottled nutes; if using soil i suggest sterilizing it before use inside.
i had once switch to mighty bomb which is basically an organic alternative spray, and i didn't like the results. I use it occasionally when i want to give spinosad a break
used the spinosad once again and haven't had the problem since
be weary of bringing other growers equipment, plants, soil, stuff from hydro store, ect into your grow space. imagine it a sterile environment and you must de-contaminate certain things before they can go in, its the first step to winning the battle. Prevention