The causative agent: fungus Marssonina rosae.
Infected pink bushes lose their attractiveness, the plant sheds leaves, then buds, and in the unfinished stage may even die at all. Black spot is one of the most common diseases of roses. The fungus has up to 50 races, so it's almost impossible to completely get rid of it.
The causative agent of the disease covers the top of the leaves, the stalks are rarer with small black, brown or dark brown spots that can grow and unite with each other. After a while, they start fungal sporulation, and the leaves themselves yellow and dry. If you do not fight this disease, then in 2-3 years this can lead to the loss of the entire bush. The best conditions for infecting and developing the disease are high humidity (above 85%) and low temperature (+ 10-15C).
In the open ground, the first symptoms of the disease are usually seen in the middle of summer, with the infection occurring in the spring. The disease can be distinguished by small black-brown specks, sometimes with yellow edges, which unevenly cover the foliage of pink bushes and grow rapidly. It is also possible the appearance of spots on young, not yet ligneous shoots.
The affected leaves begin to dry out gradually, become yellow and fall off. In case of severe infection, the bush can shed all leaves. This is especially dangerous for young and not yet strengthened plants, which start to lag behind in development. In a closed soil from this disease, the bush can suffer and dry. In open ground, it is exposed to freezing during the winter.
The causative agent of black spot hibernates well in the fallen leaves, there in the beginning of spring it begins to develop. Also a wild rose growing near a greenhouse, is particularly susceptible to this disease and distributes it to other plants. When the lack of light and the presence of plant remains, the disease occurs more often and develops an order of magnitude faster.
To prevent the onset of this disease, we recommend the following: