Using garlic spray on blackfly

Anybody successfully used garlic spray for blackfly, which I read up as a substitute for chemicals.  I made up some last week for the first time put it in a spray and because there wasn’t a lot, I then diluted it with tap water to make it go further but with the result that when I sprayed it on the blackfly it did bugger all and they’re still in residence. Should I have diluted it or simply use neat. If so I’ll make with more bulbs and more water. I used one bulb and one mug of water, but it did evaporate whilst boiling. The recipe (which was American) said use a cup, whatever that measure is).