I get incredible efficacy from myclobutanyl which is available to you as Immunox. Here in southeastern NY I control it with a single spray in mid-spring. You need to get it on the grapes before they start to spot when they're tiny.

Have you identified can lesions or are you assuming that's where it came from?

Grapes fruit off last year's wood, it's always renewal pruning. There will also be older wood present no matter how you prune. So if that old and older wood has lesions it's going to over-winter.
And I would imagine the spores travel or else once clean a vineyard would remain clean. It's doubtful that your source of infection is from the 6" or so of vine you got from the nursery.

I'm curious why you planted grapes if you thought spraying was an effort. Between bugs and disease spraying is constantly needed with almost all fruit, it's always seems to be something.
Even organic, if you're not spraying you are putting in an effort other ways.
Spraying fruit isn't the effort for me, a little time every other week when I have time. Putting up the fruit is where I find the effort because when it needs done there's not much putting it off.

Immunox is rated for black rot on grapes.

myk1, there are grapes growing wild up into 40' tall trees at the edge of my property. a few years ago, there was a small bunch of delicious seeded concord type grapes within reach.
that's what inspired me to plant grapes. i wonder if it might also be a source of black rot. there's plenty of grapevines growing wild in my area, but i rarely see actual grapes.
i try to avoid spraying, and prefer less toxic controls when i do spray. i dont know if grapes are a high enough priority to grow if they need frequent spraying.
i grow tomatoes, and only sprayed them last year [due to the late blight outbreak in the northeast] my plants didnt get it, whether from spraying or luck, i dont know. i grow raspberries, which dont seem to need spraying. i wouldnt plant tree fruit because i know how necessary frequent spraying is. i was hoping grapes were more like the raspberries, or that i'd love them so much that i'd be willing to spray if needed. i thought there were only a few clusters, a meager crop, until i went to cut out the infected fruit and saw how bountiful the crop could have been. i'm still undecided. the one time spray of myclobutanyl sounds intriguing.

I would blame the wild population.

I don't know much about organic (or neglectful that's passed off as organic) growing of grapes. I do know they are prone to a lot of assorted disease problems.
I don't know what I was thinking when I tried grapes and was organic. Maybe I figured the sulfur or copper sprays would see me through. That's probably a major reason I was never able to get the vines to live long enough to fruit. Powdery mildew can be really bad here (as last year's pumpkin crop shows). Or maybe I had it in the back of my mind that I would spray if needed.

I think you'd have better luck growing tree fruit organically or neglectfully than grapes. Bagging apples and other large fruit seems to have a good success rate for most people.
I think some are bagging their grapes but I also think that's still in the trail period. I don't know how much that would help here other than against insects and birds because of the mildew.

But if you're willing to accept only getting a handful neglect may work out for you. You'll have to stop thinking about the crop lost and focus on the crop you get. :)

ensete, where are you Your profile says zone 7, but if that's zone 7 in the southeast you will probably have more luck with muscadines.

I have black rot on my grapes and was curious if any of the following will work(and save me a trip to the $tore).

Fertilome Triple Action Plus - neem oil concentrate

Ortho Dormant Disease Control lime sulfur concentrate

Ortho Volck Oil Spray concentrate