Posted: 26/02/2015 at 13:13
If they are in pots remove any debris and burn or bin,then remove the top two inches of compost and add some fresh. Right now they should be quite dormant, so you won't have that much foliage. Get some Rose Clear and spray the whole plant AND the top of the compost. Feed them when the new foliage emerges and keep them well watered throughout the growing season. Spray every fortnight with rose clear covering the whole plant. Feed again after the first flush of flowers.
Inspect them regularly and re-spry at he first sign of any repeated infection.
If they aren't in pots the same regime applies.
The spores that cause black spot lie in the soil surrounding the plant, so removal and spraying is essential, sorry about the ashes, but it has to go.