Leaf pulling is the removal of leaves around the grape bunches, which allows the vines to dry off much quicker after rain or heavy dew which in turn makes the vines less susceptible to the spread of fungal diseases like mildew and botrytis. It also improves the coverage of spray applications, and improves sunlight penetration which helps to ripen the fruit and improve aroma.
In Germany they remove leaves early (soon after fruit set) as they believe that this helps to thicken the berry skin making the berries more resistant to botrytis. Leave are removed again just before veraison.
We've just started the process of leaf pulling. Hopefully it will be worth it as it's very labour intensive; each row takes about an hour which equates to more than 20 man days for the whole vineyard. Next year we will investigate buying or renting a machine to do the work!
It seems that I have been too aggressive with my leaf pulling; it's important not to take off too many leaves as they are needed for photosynthesis. Also, not surprisingly, Alex is much faster and only takes 30 minutes/row!