I leave some on a second year vine if it's big enough. So vine size is the key in my opinion. As with all young fruit vines/trees, I thin extra heavily. So how big is your vine? What is the caliper of the trunk? How big and long are the canes and how many did you leave? How many sq ft would you expect the vine to cover this year? Is it in full sun? These are the factors I'd consider.

Hey guys / gals any thoughts on my concerns about trimming the muscadine grapevine runners? Thanks for any help. Steve

I grow a few varieties of grapes but not sure I would call myself an expert. From your pictures, it looks like you have one or more fungal infections on your grapes. The treatment is essentially the same if it is black rot, downy mildew, phomopsis cane, etc. At the end of the season, you'll need to prune off the infected canes, clean up around the vines, and make sure that there are no infected grapes laying around. Start the vine on a spray program next year and it should clear up. My vines looked worse last year but this year I followed the spray program and they are nearly perfect. The season isn't over but I may have more grapes than I know what to do with. Although our regions are a bit different, here is the guide I used to manage the spray routine. Midwest IPM Guide

It sounds like erineum mites. If so, only esthetic. But they won't go away if you ignore them. They're very tiny mites which over-winter underneath the bud scales