There's no treating it. Just hope it doesn't cause them to crack as they ripen. It probably is chemical burn. It looks like some spray collected on the bottoms of the berries and cracked the skin. Did you spray recently? Maybe mixed too strongly or maybe just the environmental conditions like slow drying.

Thank you for your reply!

Yes, we did spray recently.. maybe the mix was too strong for unripe grapes :( I'm not sure about the grapes drying slowly, since it's not that humid in Orange county, CA, where we live :(

Thank you again for your input! I will be more careful when spraying in the future :)