Grapes and wasps
The grapevine is I believe 5 years old now. The first 2 years there weren't many grapes. 2 years ago there were lots of grapes but almost all disappeared. I figured it was probably birds. Last year I put a bird netting over it and at least got some bunches of grapes yet it seemed lots of them disappeared. Pretty sure birds didn't get to them.
I believe it is wasps that are eating them or at least stopping on by for a nice drink of fresh grape juice then the grapes just shrivel away. I noticed today that the grapes are just beginning to blush so it's time to do something.
I read about the paper bag method but not sure it would work for me as I use sprinklers for irrigation.
The only other thing I can think of is using a floating row cover. Might be difficult to wrap the whole thing up and keep it in place.