They are not generally fruitful, and are considered a 'sink' for nutrients in the early part of the growing season. Taking them off helps the upper shoots use more of the plants' resources. It also makes the vineyard look more uniform, and keeps the vineyard 'floor' nice and tidy. It is a fairly arduous process because of all the stooping and pulling involved. Angela Hobbs, left, tucks shoots carefully into the wires.
Right image shows a positioned row.
Notice the various stages of fruit set below. The grapes first shed their 'caps', and then four small flowers emerge and attempt to drop a little pollen on the sticky tip of the tiny grape beneath. If this succeeds, the grape will eventually shed the flowers and begin to grow quickly to about the size of a small pea. From this point on, the grapes grow quickly and begin to accumulate sugar and respire acid, which reduces the high level of acidity that the grapes contain after set. The grapes soften, or go through veraison , more than a month after 'set'.