Ok - I admit I'm not a huge gardener. But am facing dilemma as an obviously diseased sycamore tree in a next door garden appears to be passing it's disease into my garden. Now my bay tree has similar 'symptoms' - small white spots (looks like mould) have started to appear on the trunk. Leaves are now turning brown and falling off.

Does anyone know what this is and if there is anything I can do about it?