Rose Disease? Perth

Potted a thornless rose in August, flowered beautifully in October, now looks like it has contracted some form of disease! Leaves are drying out and shedding and dark red / brown spots are creeping up the new growth stems.

I used Scotts osmocote rose / gardenia / azalea premium potting mix from Bunnings.

I also tried propagating from cuttings in November (pre-disease). Two out of six sprouted in December, but unfortunately they both seem to have contracted the same disease.

Any help / advice would be appreciated.