So, on the margin of my back yard I have some wild, native grapevines which produce large bunches of appealing-looking grapes, but the grapes rot out and die, turning into black mummies, before they ever get ripe.

I wouldn't be opposed to some aggressive pruning on the two nearest the house, but there are many more grapevines in the woods which would keep a reserve of spores to reinfect my vines. Also I don't know that these 50' grapevines would respond well to pruning as they have been wild all their lives.

I am hesitant to use fungicides because I have Indian Pipe, honey mushrooms, and Chanterelles all growing within 100 feet of the grapes.

Any suggestions would be appreciated.