This common fungal disease that can affect many fruit, flowers and vegetables, it appears as distinct black, dark grey or dark brown spots, up to 12mm (½”) in diameter on the leaves.
There may be many small spots or just a few large spots.
Affected leaves turn yellow and drop off, and in severe cases, the plant may be completely defoliated.
Black Spot on Rose leaf
The disease over-winters on fallen leaves.
There are treatments reputed to eliminate this problem but the best cure is prevention.
This is done by clearing away all fallen leaves (affected or otherwise).