posted 3 days ago
Welcome Dave. Some context for where you are (region, zone, elevation, precipitation) helps get better answers, and that can be put in your profile (upper left of post) or signature (bottom of post).
I would also suspect deer, which eat my grapes off the fenceline they grow on. Deer can jump anything short of 8ft. They will not jump a double fence 4ft tall and 4ft apart, as they do jot have good depth perception. Elk are our biggest herbivore issue here, as they can jump anything short of 14ft and can also knock down most fences. You’d know if it was elk.
At my friend’s Willamette Valley vineyard, heatwaves followed by wind can knock grapes and desiccated leaves off, but yours do not look heat stressed or even that far along into fall color. Young, stressed grapes—particularly grafted rather than self-rooted—will drop fruit and foliage with drought. That doesn’t look like your issue though. On that note however, my friend has had much better hang time through these stressors than his neighbors, likely because of his regenerative practices with minimal soil disturbance, interspersed tree plantings, self-rooted vines, and many of his are over 40yrs old.
It looks like something that could not reach the top wire grazed on it. Some regenerative vineyards have started using short legged sheep to do weed management and leaf thinning very similarly to what looks like happened at your place, of course timed to not take all the grapes.
This is all just my opinion based on a flawed memory