Barbara, from painful experience with rampant blackspot I have found that the saving grace for me is my Gardenville Sea Tea. I have had Blackspot to the wazoo and the incessant rain is not at all helping! But my roses keep fighting! I've got very thick strong canes and each leaf that falls off bunches! of new ones quickly grow to take their place. But I'm very new to roses and am taking the big risk of continuing to feed my severely defoliated roses through the entire fall period until the temperature starts to really get chilly-- maybe as late as mid-October? We usually don't get our first frost until the last day of October. I am borderline zone 5/6. There is another raging debate right now whether to deadhead, whether or not to fertilize through the fall. Just a few like myself fertilize through the fall. Their roses have done fine. I will have to wait and see what happens to mine since this is my first year gardening and! growing roses. I decided to go the fertilizing route also! because my lawn company always applies winter fertilization for the grass the last week of October. I sort of did the common sense guessing is that roses love fertilization no matter what; but that they are smart enough to know that once that temperature gets really cold and the sun starts to fade that it's time to slow down and get ready for sleeeeping. It's like trees. You can keep fertilizing but they'll still know it's time to drop their leaves and rest during autumn-winter.

What kind of soil are the roses growing in? If you feed the soil, if the soil is a good, healthy soil your plants will be strong and healthy and better able to ward off plant diseases. I have found that either of these mixtures, 1 teaspoon of baking soda in 1 quart of water or a 50/50 mix of fat free milk and water, will help control Black Spot.
Contact your local office of the Purdue USDA Cooperative Extension Service about having a good, reliable soil test done and also dig in with these simple soil tests,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to see what needs to be done to make your soil good and healthy that will grow strong and healthy plants that are better able to figth off plant diseases.
Vitamins are not needed.

Here is a link that might be useful: Purdue CES