
If the entire leaf is yellow, there may be a nitrogen deficiency. Also, over-watering displaces oxygen and leads to yellow leaves. If the leaf veins are green, then a different deficiency is present, possibly low iron. If you feeding the plant on a regular schedule as recommended on the fertilizer container then you probably don't have nitrogen deficiency. If you have experienced lots of heavy rain, it could be that the soil isn't draining fast enough. Improving drainage means lifting the roses to dig amendments into the soil. Read this article for further information: https://www.gardeningknowhow.com/ornamental/flowers/roses/yellow-rose-leaves.htm