You've already received good advice, but I'd that you should probably repot the plant. The fungus that causes this malady ('Diplocarpon rosae') lives in the soil and will over winter. There are soil treatments you can use. Here in the U.S. 'Dormant Oil' is a brand name... but it's nasty smelling since it's sulphur based. Since your rose is a patio plant, take it out of the pot and replant it this fall after it goes dormant.
It'll help (next year) if you make sure you don't water the plant by dousing the leaves... water only the soil underneath and make sure you don't splash water on the lower leaves, since it spreads any remaining fungus...