I have 4 standard rose trees in my south facing garden in planters. They have plenty of flowers but the leaves keep falling off.
I have checked for any infestation but haven't found anything.
If the temps where you live have been hot or you are in the middle of a heat wave, that could explain the leaves falling off. The roses will let some leaves fall off in an effort to create better air flow through the bushes and thus keep cooler. If the foliage gets real thick and some of the foliage becomes shaded by other foliage, the rose tree bushes will also let the leaves drop off. Being shaded they are no longer performing as needed by the bushes, so it lets them fall off. Just keep them watered well and perhaps even water them all with some water that has a product called Super Thrive in it. The nutrients in super thrive help them deal with any stresses or shocks they may be going through, so that no more serious issues arise.