The second method is to net the crop. The most common and least expensive netting is the lightweight, black, polypropylene type with a square mesh size of ½" x ½”. This can be difficult to install and remove as it tends to stick to itself and to the vines. However, it is effective. Woven mesh bird netting is also effective and easier to work with but is more expensive.
If your trellis has a wire at six feet high, purchase a net that is at least 14 feet wide so that it can be draped over the grapes and secured along the bottom edge with clothes pins. Nets that are 17 feet wide are less common but give more material to work with and are therefore easier to secure. (Ward Upham)