How to treat Diplocarpon rosae black spot fungus disease
There is no treatment to cure this disease but you can avoid it from spreading or prevent from infecting your plants.
Remove infected leaves or any infected parts of a plants immediately as soon as you spotted.
Cut the infected leaves with scissor as shown in image below:
But make sure do not cut the new shooting leaf and bud as shown in image below.
Through them away or burn them but do not keep them in same area as its germs drift by the wind and infect the nearest plants.
Pick up all the infected fallen leaves from the ground. Through them or burn them. Do not keep them in same area.
Do not water on to an infected parts of plant as this will spread to other leaves and parts of plant because the water as well as wind help this disease to spread.
If you want to, you can apply Neem Oil by spraying on to the plant after removing the infected leaves or other parts of plants or before the disease starts to prevent from getting this disease.
you can use Neem oil also for the treatment of Aphids which are also called Greenfly and Blackfly.