The symptoms pictured look like Black Rot, a very common fungal disease to which grapes can be very susceptible (there are no resistant cultivars). The linked page provides more information, but essentially, there is no treatment which will cure existing infection. Preventative fungicide sprays can be used next year, starting in early spring and continuing as long as the product you choose to use instructs (several repeated treatments will be needed every year). Remove all symptomatic, infected debris in the meantime (both now and this winter) so it doesn't harbor infectious spores for future outbreaks.

Miri

Thanks so much for the very quick response. I’ll try to be ready for next year.

On Monday, August 5, 2024, 12:30 PM, Ask Extension <<personal data hidden>> wrote:

You're welcome.