I am not an expert,but I have several young bay that I have grown from cuttings ( I started with 20 cuttings and ended up with nine that have rooted,in a heated propagator ) The tree I took the cuttings from is about eight years old now,and since using my rose spray ( Rose clear ) it has kept far better and looks very healthy.Previously,it seemed to suffer from the same problem as you are having now. I used to nip out the brown leaves ,but no need now.
There are lots of far more experienced people than myself,who can probably help you better than I. Most of what I do in my garden has been through what I have learned from GOY