What may happen if a vine is pruned before leaf fall?

Pruning a vine before leaf fall can indeed weaken the vine. During the winter, vines store energy in their woody tissues, and this process is linked to the leaves. If pruning occurs too early, while the vine is still actively photosynthesizing, it can disrupt this energy storage process. The vine needs its leaves to convert sunlight into energy efficiently. Therefore, removing leaves prematurely can result in a reduced ability for the plant to build up the resources needed to survive the winter and to flourish in the following growing season.

Additionally, a vine that has been pruned before leaf fall may be more susceptible to stressors such as diseases or frost, as it hasn't had the chance to prepare adequately for the dormant period. This increased vulnerability can lead to overall health decline and reduced vigor in future growth cycles. Hence, early pruning can indeed compromise the vine's strength and productivity in the long run.