Question
I have noticed mustard yellow marks which are raised but no bigger than pin heads on the under side of the leaves the appearance looks powdery but is firm, I have not seen this before is it a common problem and does it need a remedy? please advise.

Answer
What you are describing is called Rose Rust. It is a fungal disease usually caused by dampness or a long dull spring. Some roses are very prone to it but most are not. You may have a cultivar that is prone to rust. The spores are usually on the underside of the leaves. Use Orthos Rose Pride Spray but make sure you get it under the leaves as well as on the tops. I would even spray all around the base in case some of the spores are lying on the ground and could re-infect. If you get this rust problem next year or it come back again this year, then your rose is prone to this disease and you will get it every year.