Why is a renewal spur left on a grapevine?

Leaving a renewal spur on a grapevine primarily serves the purpose of producing new wood that is essential for next winter's pruning. The renewal spur consists of a healthy, young shoot that can develop into a fruitful vine for the upcoming growing season. This new wood is vital because it will support the growth of fruit-bearing shoots, which are necessary for grape production.

By retaining this spur during pruning, a grower ensures that the vine has the potential to generate vigorous new growth, which is critical for maintaining the health and productivity of the vine over time. This practice helps to replace older, less productive wood with fresh growth, ultimately enhancing grape yield in subsequent seasons.