Where are you that you would be harvesting a North American grape species, Vitis labrusca, in May?
Question aside, the answer is no.
The vine continues to store starches in its roots, made from photosynthesis, to be used during the following budding season. If you want to reduce next year's crop, cutting off the vines while they are still in photosynthesis is an effective measure.
If you want larger fruit, give them more water.
If you want better quality, drop (cut off) a third of the clusters.
How many buds are you leaving when you prune?