Vine Damage...

Can anyone help me figure out what might be causing the damage seen in the photos?

I am located in south central PA; and it is occurring without a pattern on multiple varieties including Concord, Can Franc, Chardonnay, Vidal Blanc, and Bianca. The vine appears healthy one evening and the next morning the tip will broke and usually hanging by a fiber or two. In the following days leaves seem to be cut and the vine may break again just below the original break.

It is one of the grape stem borers that does this. Early in the season overwintered adult lay eggs on the shoots and the yound feed inward often several in a line encircling the shoot so they break off easily. If they don't break off and you see the small holes in a circle, break the shoot near it and you will usually vine a vine cane borer in there feeding away. They generally aren't serious enough to worry about controlling.

Thank you much for the quick reply!