Iron is one of the many elements that gives our roses beautiful, lush green foliage while preventing discolouration and premature leaf fall.
A shortage of iron in the soil can cause leaves with large yellow areas and fine green veins. The young leaves will be the worst effected and almost completely yellow. Also note that flowers may appear to be smaller in size. Alkaline and calcareous (limestone based) soils are most susceptible to iron deficiency.
Apply Iron Chelate.
Alternatively you can buy a pack of Trace Elements from your local garden supply shop. It is chrystals that you can mix into water and pour onto the ground around the affected plant. This is to be used once only in most gardens but may need repeating in well used soils.
Any treatment will take a couple of weeks for you to see signs of improvement in the new growth.
Important: signs and symptoms will vary significantly between varieties, even within similar categories. The information provided here is a basic summery of the most common affects and will not always be applicable to all rose varieties.