We moved into a new home three years ago. The house had concord grapes growing. The first year we got bushels of grapes from the vines. Last year we ended up with a much smaller crop... only about two bushels. This year there is no fruit growing. I have never cut the vine back and the vine is out of control. I want to prune them back but am not sure how much to take off the vine or when the best time to prune is. Any help is appreciated.