Grape Vine Disaster

When I looked at my grapes yesterday, they were simply beautiful hanging from the arbor. The bunches were looking fine and healthy.  I checked them for picking, but were not ready yet. Today, I couldn't believe my eyes, just 24 hours later. Nearly every bunch of grapes turned brown. Some are completely brown, some partially.

I  did a quick Google search to see what on earth this could be. I read about black rot, but it looks different than this, with the grapes all shriveled like raisins. But perhaps my grapes are in the early stages of that. These grapes are still fully formed and firm to the touch.

Some of  partially brown grapes have a line of division that is perfectly straight, reminding me of an equator on a globe.

If it is black rot,  I read it is exacerbated by rain. As I mentioned, we've had a particularly rainy summer.

I won't lie, this is quite a disappointment. It was the first year this vine produced such a large amount of fruit. But that's the way it goes with gardening. There are no guarantees.