I've never tried it, but it's supose to stick to the plants. This makes the herbicide more affective.You can buy surfucants made for this that is almost the same thing.
Agree! "Soap" = "Surficant", etc. Also, add a little food coloring to the mix so you can mark where you sprayed...preferably a contrasting color to your vegetation.
Soap will help product stick to the plant but it is not as good as using a surficant. Surficant is cheap and causes the cells to open up to accept product. Much more efficient.