Rt - you garden in Canada. It's a lot different than most of us. The long cold winters help keep down a lot of insect pests and diseases. For me the powdery mildew will kill my squash eventually, though not real fast. (On the other hand my huge old lilac tree gets PM every summer, but it never really bothers it, it is just a cosmetic issue.) You probably have less trouble with SVB's due to your climate also.
But yes, a worm in the roots would be different from the vine borers which attack the stem above ground. I know there are wireworms and nematodes that attack roots, but I don't know much about them.
And yes, Dawn is a detergent not a true soap. A lot of people report that detergents burn plant leaves (depending I suppose on the concentration used and the plant and other factors about how applied, etc). If you try again use soap, which would be something like Dr Brunners, Murphy's oil soap, Ivory soap powder (the kind that says 99 99/100 pure) or shavings from a bar of soap in water.