We had a little discussion about what kinds of "soaps" to use. I have used several types, but some recommend only dish SOAP as opposed to any dish detergent. Dr. Bronner's makes pure castille soap in liquid and bar form. I have used that for a long time (the peppermint).
The only thing I would say is be careful of liquid detergents with too many grease cutters and additives. Check out the kind of liquid detergent you will use to make the spray if you go that route. I've had good success with some of them in the past (Dawn, Palmolive, Ivory). But companies sometimes change their detergent formulas and the high-powered, harsh detergents can strip plant oils and kill some plants.
I do like making insecticidal soap at home. Good frugal and useful tip.