I'm having the same problem. Botanigard claims their WP22 is safe for cannabis if used no later than 3 weeks before harvest. I've used it with with younger plants with some success, but have even hesitant to try it on plants as close to harvest as mine. So...
Yesterday I pulled all my mature plants out of their tent and setup a four stage decontamination station
#1 Isolate infested plants together.
#2 One by one pull the plants and use vacuum air to blow as many flies as I could see off the plants
#3 Neem oil the surface of the soil and clean their pots with a bleach/water solution
# 4 Isolate the cleaned plants
Then I did a thorough cleaning of their tent and everything in it with a bleach/water solution. I waited about four hours to let the bleach smell die off a little and put the plants back in with yellow sticky bug catching pads.
This morning I had caught 3 whiteflies on the stickies - a great improve over the HUNDREDS I was getting everyday before that. Hopefully, hanging sticky pads everywhere I can inside the tent will keep them from getting out of control again between now and harvest.
Good luck with your grow!