Did you have a cold spell? Did night time temperatures dip below freezing? The darkened leaves is typical of cold damage. These plants are about to go dormant anyway and may look ragged.

Apart from early frosts, I would imagine this can also be caused by over-watering which can lead to phytophthora root rot which there is no chemical remedy. I would cut it back hard to outward facing buds as you have nothing to lose.