For preventatives, I alternate between Propiconazole 14.3% and Compass. Most people have a heart attack when they see how much Compass costs (understandably so). However, it's a granule in a container that lasts years, unlike liquid concentrates which can have a shelf life, and the dose is only about 1/4 teaspoon per gallon of water. I have large gardens and I bought it years ago for about half of what it costs now, but even then I considered it a long-term investment (more like a pre-paid expense).
Read the labels for frequency of applications.
For contact fungicide I use what used to be called Pentathlon DF (now Manzate Pro Stick). I use it with Indicate surfactant (sticker/spreader). It's sulfur based and leaves yellowish water spots on leaves which I dislike, but it kills the blackspot.
All of these are available at Rosemania at
http://rosemania.com/page5.htm.... However, not all products are available for sale in all states, and some can only be sold to licensed professionals. For instance, Pentathlon can no longer be sold in New York, but I purchased a significant volume of the powder years ago, and am allowed to use it up. But once it's gone, I'll switch to an alternative.
I also use the Hudson brand four gallon battery backpack sprayer, which is probably available on Amazon. I also use a respirator, nitrile gloves, long pants and long sleeved shirts and hat when applying these fungicides. Always read the Material Safety Data Sheet to understand the chemicals involved and whether you are comfortable working with them.
