I've had to use bird netting for years. Usually I will put the nets on as the grapes start to change color. I have to laugh, when I start testing for sugar so do the birds. But anyway I will trim the vines back so I don't have a big problem with the tendrals at this point. I have had to learn how to close the netting tightly and around the stalk of the vine I will fill this gap with newspaper as the darn birds will actually get inside the netting. I only have five vines of merlot and five Zin vines so I have to protect the small crop that I have. But I have never really had an issue with the tendrals.
Good luck.
Lisa