Welcome to GoY.
I asked this last week but got no really definate answer.
It was suggested aphids caused it but I've never seen any on it. It was also suggested it could be due to the dry weather. Maybe that's a contributing factor. I am still baffled....

sounds like lack of water and or sun to me .

Check the plant for signs of mildew, (powdery greyish white spots or covering) - this can cause this trouble.

many thanks,Hywel,Noseypotter,&Bamboo for your replies.Well no aphids,spots,or powdery mildew,the plant gets plenty of sun,so I guess it must be the hot dry weather and lack of water....It was full of buds and would have been lovely, so very dissappointed,have treated plant for fungal infections anyway,so I must remember to give it more water In future !!

not to worry it will be better next year.