Today 
Leaves and sometimes stems are marked by dark blotches caused by a fungus. The spores overwinter on fallen leaves, stem lesions and bud scales, and reinfect the plant the next spring when there's a flush of new foliage. If these leaves are then infected, they too eventually turn yellow and drop. If not dealt with, the plant will weaken.
Rose black spot is very similar and can be dealt with in the same way.
Solution
Organic
Fallen, affected leaves must be promptly destroyed, along with any stems showing signs of infection. The best way to avoid the problem - which thrives in warm, wet conditions - is to lay a thick mulch around the plant. This helps lock moisture in the ground, and stops rain splashing the spores from the soil on to new growth.
Chemical
Spray with a fungicide containing penconazole or myclobutanil. Begin spraying each fortnight from early spring, just as the new foliage emerges, as a preventative measure.
