Newfruitgrower:

I have 3 concord and 2 canadice vines. I do not know
how well copper controls blackrot. I can say I use
Captan 50 WP at rate of 2 TB/gallon and I never get
black rot.

I believe blackrot is best controlled by spraying EARLY in the season. I spray once prior to bloom and then just
after fruit set (2 more sprays two weeks apart).

Your grapes have black rot. A common grape disease. .

Copper is not very effective against black rot. Might be if you lived where it wasn't a serious problem - but apparently in your area, it is a problem.

In a lot of places, it is very difficult to control black rot unless you use a chemical fungicide. Captan is similar to copper against black rot, which means it won't work when the disease is at its worst.

The most effective control of black rot is mancozeb applied early - at new growth and at pre-bloom. if you can squeeze in a post-bloom spray, that would be a plus. However, there is a 66-day time to harvest so that may not be possible (the first two are the most important, anyway)

This is just general advice. The best thing would be to follow the recommendations of your State Extension.

I think the best material to use is not mancozeb but myclobutanyl, safer, rain proof and available to homeowners as a product called Immunox. I generally get full control with a single application about 2 weeks after apples have lost their petals (grapes are secondary to me). This year that was round the first week of June.

I've been using it for over 20 seasons at several sites. Even protects the more susceptible seedless varieties.