I have been trying to grow Concord seedless grapes in Buffalo NY for a couple years. I think I have figured out how to prune them and last year was diligent throughout the growing season to prune back the canes so that more energy went into the fruit. It seemed to pay off as I had a number of nice looking clusters of grapes. However, as the season went on, around the end of August, I noticed the grapes splitting and then rotting. Needless to say, I got very few edible grapes.
I have uploaded a picture of what a cluster of grapes looks like that had this problem. Is this caused by lack of the correct nutrients or from some kind of pest? How can I avoid this happening this year?