First off Dithane is a protectant meaning it is a preventative fungicide and will not help that much if you have a disease situation. Share your issue with us and the folks here can be if more help. I dont know of any issue with applying it to grapes following the label, but it might not help depending on what you have going on.
I have a Phomopsis problem, lots of lesions on the canes. This has been going on for years and did not know what it was till recently. Thought it was a Black rot problem cause leaves get affected to. But found some pics of Phomopsis and that's exactly what it looks like on the canes at least.
Dithane info I found says it wont cure it but will just stop it from spreading, says I have to use it early next year to try and prevent it from happening again. But I am by no means an expert at growing Grapes. Only my 5th year trying to get just one decent cluster to grow and nothing but problems here in PA/USA. Had to cut them way back down to 2 feet tall 2 years ago cause something hit them hard. Now with 2 year old wood I am seeing for first time some nice Clusters forming early, but here I go with the Disease again that hits them every year for me, same exact thing since I been trying to do this every year.
I been using Neem Oil for a few years, applying it every 7/14 days, but it does not seem to stop it. So was going to order some of this Dithane and try that.
Also this destroys the new shoot leaders trying to grow and they just end up shriveling up and dying off. The leaves get small brown/black spots on them and the edges turn brown and curl up. Never see any insects on them and hardly any holes in the leaves from insects munching away.
I only have 8 Vines so do not want to buy any of these $300 fungicide treatments I saw online with Sulfur and so on, not worth it to me and this Dithane I saw was only like $12 on Amazon for 6 oz powder.
Just trying to figure this all out so one of these years before I die I can learn to grow grapes the right way
You probably have multiple problems causes the grapes demise. As far as I know dithane does not hurt Concord. It will help protect from Black Rot, Phomopsis and Downy Mildew since it is a mancozeb product. It does not protect against Powdery Mildew and must be discontinued 66 days before harvest.