Wow! I don't think you realize how much information is needed from you to fully answer your question. First, using drip saves water, but isn't necessarily the best method for preventing black spot. It's the humidity in the air, not actual water on the foliage which causes the problems. But, if the roses don't get enough water, they'll be more suceptible to disease. You may wish to check that out, first. Do you fertilize? What do you use, how much and how often? Under nourished plants are also more likely to contract disease.
You state you've "used various rose sprays", but don't mention any other than Daconil, which is a good, low toxicity fungicide. You don't mention how often you've used it; at what concentration; for how long; nor how it's been applied. I encounter people all the time who figure you can use a trigger bottle, like an old Windex bottle, to apply chemicals to their roses. Nope. You need either a hose end sprayer which permits you to vary the concentration, or a pump sprayer, so you can fully cover the upper AND lower leaf surfaces.
You appear to live in an area where fungal problems are more severe, which means you'd better begin your spray program early, in anticipation of the diseases getting started, rather than waiting until you see them in your garden. Have you removed all of the diseased leaves from the plants, raked them from the area and then mulched, before spraying, to remove the source of reinfection? You also don't describe the growing conditions, such as available sun hours and quality; air circulation; how crowded your roses are, etc. What type of roses are the worst offenders? Which cultivars are the worst?
You can virtually eliminate disease from your roses, but it takes a multi step approach, begun early and maintained religiously (depending upon the heat and humidity in your area). Daconil is good, as are Serenade (organic) and Immunox (inorganic), but they have to be started prior to the problems and repeated properly per package instructions. The greater the level of housekeeping you perform in your rose beds, the greater your chances of success. If you don't get enough sunlight to dry out the area, you're going to have difficulties. If the plants are too crowded, you're doomed to failure. Other plants included in the rose beds (companion plantings) may crowd the roses, reducing air circulation and competing for food and water. Surrounding shrubs, such as hedges, can have similar effects. If your roses are planted too closely to walls or fences, you may have too much reflected and radiant heat, causing more perfect conditions for disease to flourish. If the varieties you've selected are known for suceptibility to disease, you may wish to rethink your choices and select more disease resistant roses.
There are simply too many unanswered questions here for anyone to be able to tell you what to do to correct your blackspot problem. I hope this helps.
