Good Morning, 

Thanks for your question. 

We do not generally call people. We are volunteer Extension Master Gardeners. The information below will give you more details than I have first hand knowledge about black rot on grapes. 

Please click on the following link about growing grapes: https://extension.umn.edu/gardening-minnesota/growing-grapes-home-garden#diseases-and-other-challenges-986261

As you scroll down, it discusses pests and diseases. The information states: 

Fruit rots

Common fruit rots of grapes in Minnesota include Botrytis bunch rot, black rot, phomopsis, anthracnose, and sour rot. These fungal diseases can cause complete crop loss in warm, humid climates.

You may be having hot and humid weather lately as we have had in the southern areas of the state. 

Here is another current webpage about black rot on grapes: https://blog-fruit-vegetable-ipm.extension.umn.edu/2026/06/black-rot-on-grapes-guignardia-bidwellii.html

This has links to other reliable websites about management.  

It appears the link to the Midwest Vegetable Guide is a dead link on the above website. Here is another valid link: https://mwveguide.org/

Good Luck!