Posted: 23/05/2017 at 23:32
Have you or your neighbours been using glyphosate on the garden? It doesn't look like any of the usual problems such as mildew, black spot, rust, aphids etc.
If not it could be rose rosette virus, in which case you need to report it. Here is what the RHS says:-
This could be the result of virus infection, but a much more common cause is contamination of the plant by the weedkiller glyphosate. The leaves described above often develop in the season following contamination, in small clusters of pale green or pinkish-red leaves, resembling mini witches’ brooms.
Rose rosette virus, transmitted by microscopic eriophyid mites, is a problem in the USA and Canada, but is yet to be confirmed in the UK. Some of the symptoms produced are very similar to those caused by glyphosate contamination as described above. If you can rule out glyphosate contamination as the cause of the symptoms affecting your plant, and suspect that Rose rosette virus could be responsible, you should report this to the Animal and Plant Health Agency (APHA) on telephone number 01904 405 138 or by email at firstname.lastname@example.org
The whole article on pests and problems is here -