Established grape vines usually consist of a major trunk with several older, dark colored vines extending outward on a trellis or arbor. After several years, the older vines may become too numerous and some of them may need to removed clear back where they are connected to the main trunk.
Lighter colored vines extend from the main lines (and sometimes directly from the trunk). These lighter colored vines were produced last year. If most of these vines are allowed to remain, growth will become too thick and fruit will be limited because of lack of light. Some of them may need to be removed completely back to where they connect to the older, dark colored vines. Most of the lighter colored vines should be shortened to a few inches, leaving only 2 to 4 nodes where new shoots will grow. These nodes will produce flowers and fruit. By limiting the number of fruiting buds, vines produce larger clusters of grapes with larger fruits in the cluster. Some of these short vines may need to be tied to a wire or trellis to give them support.
Shortly before harvest the lower leaves surrounding the grape bunches can be removed to provide better sun exposure. This helps to ripen the grapes and also improves air circulation, which helps to prevent disease infection.