Answer: Based on your description of the fruit turning to "raisins" on the vine, your grapes may be suffering from a fungal disease called black rot. To prevent it, keep the vines well pruned so air can circulate and sunlight can penetrate the vine, keep the around around the vines weeded, and practice good sanitation by cleaning up all prunings and fallen fruit or foliage promptly and disposing of them in the trash. The fungus overwinters on plant debris and reinfects the plant the next year, so the clean-up aspect is very important.
Peach leaf curl must be prevented by spraying in the fall or very early spring, so unfortunately it is be too late to control that now once the symptoms appear.
I would suggest you consult with your local Cornell county extension to make sure this is black rot and peach leaf curl and to get their control recommendations. If a chemical control is recommended, they will have the most up to date information on what to use and how/when to use it for maximum results.
As far as the squirrels, you may be able to net the tree, or you might have success using one of the spray on or granular repellents labeled for squirrels. Read and follow the label directions for applying and reapplying the repellent.
Good luck with your fruit crop!
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