I have had some very useful discussions on this group recently,and particularly with regard to removal of sub-laterals or sideshoots during there vigorous growth in the summer.My latest advice found by talking to vinegrowers in England is as follows.Herefordshire in England is not a high rainfall county as the average rainfall is about
28".1) I have noticed myself,and this is confirmed by others,that new vines (say second/third year) can be considerably more fruitful than older vines.This is believed to be because one trains a single shoot initially up a 5' cane to initially form a single Guyot cane for the first cropping.In forming this single cane,one is advised to remove all sideshoots.
2)Vinegrowers have told me that whenever possible,they pinch out some of the sideshoots when small,but later prune them back to one leaf.The idea from some is that leaving one leaf helps to feed and mature the adjacent next years fruit buds.3)Another point is that from middle summer,energy should not be wasted in forming sideshoots,and these sideshoots get in the way of efficient spray coverage for powdery mildew.
So I am still unclear about the contribution made by these sideshoots.By removing them early,they cannot produce large enough leaves to provide energy input for ripening the grapes.So one would rely on the 4' of leaves on the main vertical lateral.
Comments very welcome. Michael