Rowan treeWe have had our Rowan 4 years and has grown steadily

Although we have had plenty of rain, I wonder if it has managed to find its way down to the roots and not evaporated from the surface. I would dig down a little and see how wet the soil is before trying anything else.

Ok thanks i will check that....

I have checked as you suggested but it seems quite damp. I have also noticed whitish lichen growing at intersection of branches

If it is white lichen then it just means that you have clean air so not a problem. You could go down the road of spraying with a fungicide or let the plant take its natural course and see what next year brings.