Rose question

I have a very large rose (2 metres tall) which has been infected by fungal disease. Despite much spraying and removal of dead leaves etc, it has dropped nearly all its leaves and is pretty bald. Should I prune it hard now (reducing it to about 1/2 its current size), or should I let it carry on looking rubbish until the autumn? I know you're supposed to prune in the autumn and spring, but does that also apply in a situation where the plant is ill?

 

If no one posts anything to the contrary, I am going to give that rose the hair cut of its life.

 

black spot I think. Leaves turned yellow and fell out in masses. Plant is bold for the first 120 cms up or so. There are still some leaves after that, but not many.

 

Thanks for your advise, wiseoldowl. Ok, I'll collect the dead leaves from underneath (I have done it before, but I probably overlook some!), and I'll keep spraying, even though it looks as though it is not helping much. The plant's so big I use up half a bottle every time I treat it (which is getting quite dear).