Let's be clear here........I wasn't saying that "supermarket" peppers like jalapenos and such would not act as a deterrent. But for sure, they won't kill off an entire mite population on plants. I have not tried capsaicin, but have tried most every pepper my local supermarket has to offer- the ones readily available. In veg, try them all, what the heck. In flowering, all these peppers impart a "hot" spice to the flowers, irritating the mouth, throat and lungs to most smokers. I've tried numerous ways to remove the pepper residue, i.e. spraying them down, dipping before and after harvest, etc..........and it would appear since the peppers are oil based, nothing had much effect on reducing or removing the "burn" while smoking. Very irritating!
It's also important to realize what you are getting yourself into while mixing the concoction and spraying it around a room. It's nasty stuff so don't let it touch your skin, don't breathe it in, etc. Boiling up the mix also will give your kitchen an irritating vapor for a few hours too. Just not worth it, IMO. If you have a small room, a couple plants- I can see the possibilities maybe. For me, typically 24 plants grown at a time- no friggin way, never again.
Coming from an organic background (I ran the U.S. 2nd largest organic farm- 875 acres) for a number of years, I am always willing to give "organics" a try first. When it comes to mites, they are such tough buggers- better an atom bomb than a firecracker if you want to save a crop. Everyone has an opinion, especially on mites. I fought them for many years, crop after crop- they'd just keep showing up 2nd or 3rd week of flowering not matter what I did. Now I am mite free, 3rd crop in a row. I've detailed previously what I did to finally eliminate them, but not sure if it was in this thread or one of the other 500 mite threads on RIU...........