The winemaker, in conjunction with whomever is in charge of labour, also has to decide at what time of day to pick. In hot climates grapes are generally picked either at night (easier by machine with big spotlights) or very early in the morning in order to deliver the grapes to the winery as cool as possible. In the old days grapes would be thrown into the back of trucks and sit in the sun, often squashed and increasingly oxidized, so that they arrived at the winery having lost a substantial proportion of their primary fruit flavor. Nowadays any winemaker with pretensions to quality will insist that grapes arrive as cool as possible in small stable units, typically little plastic, stackable boxes which keep the bunches whole (although whole bunches are an impossibility if the grapes are picked by machine since they operate by literally shaking the grapes off the vine).
Machines are used increasingly in the vineyard, not just for picking but for pruning and lifting wires and therefore the canopy during and lifting wires and therefore the canopy during the growing season. But the greatest wines in the would are still picking by hand, no matter how expensive and elusive the pickers, because they can not only snip whole bunches off the vine but also make intelligent decisions about which fruit to pick.