I think the use of soap to 'clean-up' crops is to unstick such as aphids and caterpillars, the alkali nature also irritates them, and allows more toxic chemicals to work, rather than run -off as if a ducks back,so to speak. Liquid detergents mainly are oil derived and not for food crops .Traditionally horticultural soap was "soft soap", applied with a brass syringe once dissolved in water. Simplest to obtain today would be Lux or Fairy hand- washing powder. Interesting research with the alcohol- based hand sanitizer would demonstrate that one could 'dissolve' caterpillars and beetles etc, but its probably outlawed by the Geneva convention.
Note: a wasp disintegrated into three body sections can still sting you!, but only from one end.