Insecticidal soap differs from your average dish soap (technically a detergent) in one crucial respect: it replaces the sodium in the recipe with potassium or another cation with much lower toxicity to plants. There are other differences... the surfactant is based on fatty acids not organosulfates, the other random ingredients are mostly missing. I like to use the dedicated product but I suspect it matters much less if you properly dilute the dish soap before use. Too concentrated and you start to see residue and toxicity to the plant, without any benefit against pests.
https://en.wikipedia.org/wiki/...
