This Maple is a few years old and has been pretty healthy so far down in Melbourne.

Some info which might help: The area is known to have lots of clay, dig down 50cm and you'll hit it. The lawn has an automated sprinkler system that runs for 10mins every other morning. It's been very hot over the past few weeks.

I noticed that a lot of leaves are showing this problem. Does anyone know what it is and the cause?