Hi Kerri. That is shade cloth, one of the most effective methods of reducing the impact of too much sun on grapes. Hiding the clusters behind shade cloth can minimize sunburn and dehydration by up to 40 percent, and can reduce the temperature of the space around the grapes by as much as 8 degrees F. The shade cloth, which is affixed to the trellis at the height of the grape clusters, is made from UV treated high density polyethylene, and protects the grapes from ultraviolet, visible spectrum, and infrared light. Shade cloth is expensive (wrapping a one-acre vineyard can cost $700 or so), but for a winery making expensive wine, losing 10 to 15 percent of the crop due to sunburn and dehydration is even more costly. Wine made from sunburned grapes feels very coarse on the palate, and wines made from dehydrated grapes have all the charm of prune juice.