Regular spraying with a fungicide is key to controlling and eliminating blackrot. The other thing is variety, concord and other tried and true varities are fantastic grapes. All the fancy non juice grapes im going to pass on. You can see the issues are gone quickly. Like any disease with blackrot you should spray it and eliminate it then don’t spray unless you need to. Most pears and grapes i grow spray free now and have for years but the second I see a disease I eliminate completely if I can. Some pears such as fireblight susceptible types need a spray of copper every year. Cherries cannot be grown here without a fungicide sprayed a few times a year. .
If you do use captan and immunox i would recommend protective wear eg. eye protection and gloves.