Diplocarpon rosae is a fungus that creates the rose black spot disease. Because it was observed by people of various countries around the same time (around 1830), the nomenclature for the fungus varied with about 25 different names. The asexual stage is now known to be Marssonina rosae, while the sexual and most common stage is known as Diplocarpon rosae.
It seem the black spot disease treatments for both roses and fruit trees are similar. The article below suggest us to spray with two teaspoons of bicarb soda in 5 litres of water, add a couple of drops of detergent or a couple of drops of seaweed extract and use sulphate of potash and give them about 100 to 150 grams per bush about four times a year.