Here is my sprayer ... a 12-gallon Mantis Spraymate that makes applying fungicide to 800+ roses as effortless as it can be. One full batch in this baby will do about 3/4 of the garden, coating the leaves of susceptible roses with a fine mist of fungicide. (I don't spray the ramblers or other large roses that aren't bothered by blackspot.)
My fungicide of choice right now is Honor Guard (the generic form of Banner Maxx, available from Rosemania.) It is highly concentrated, and this one-quart bottle will last about two years. For smaller gardens, I recommend Bayer Advanced Disease Control, which is available at Lowes and local specialty nurseries.
I believe in the use of fungicide to keep blackspot and other fungal diseases under control. The use of a systemic, which is labeled for application every 14 - 21 days, means that I am exposing the environment (and myself) less frequently. Though I use fungicide, I do NOT use insecticides of any type in my garden ... nothing at ALL ... no organics, no insecticidal soap ... they all kill and I'm not getting into a cycle of playing Mother Nature. I let the good bugs eat the bad bugs, and the garden stays mostly in balance.
I also believe in using a product that treats problems directly. For this reason, I do not use (nor do I recommend) soil drenches for control of blackspot or insects. If I have something wrong with the leaves of my roses (blackspot), I apply a product to the leaves to treat the problem. I also don't recommend combination products (some products have insecticide and fungicide combined ... some drenches even have insecticide, fungicide, and fertilizer.) In my garden, fungicide gets sprayed on leaves, fertilizer is applied to the soil, and insecticides are not allowed.
Decked out in long pants, long sleeves, rubber gardening shoes, with my safety glasses and mask, it only took 2 hours this morning to walk the garden with my sprayer and use up all 12 gallons ... which was enough to do everything but the back half of the Rose Field. Normally I would have mixed up another couple of gallons of spray to finish the job, but I was hot and tired, and the breeze picked up, and I decided to do the rest of the roses tomorrow.