wrote:

I grow roses as a hobby. This year has been especially bad for black
spot because of the abundance of rain. What is the best thing to use
against black spot?

Where are you located? Take a look at the fungicides recommended
locally for blackspot. Here's a website for a nursery located in
Florida that lists of fungicides by cost, disease and danger category:

http://www.rosekinggardens.com/faqs/spray_reference.htm

Availability of some fungicides depends on what has been approved for
use in individual states. Some less toxic but very effective products
are also very expensive. So there's a broad range of options available.