What has the watering regime been for your tree this year Valley?
At first glance it looks to me like it could be inadequate water getting to the leaf margins.
If that's so it could be caused by hot dry winds evaporating the cells faster than the moisture in the leaves can be replaced.
Or there could be a root problem that is not allowing water to be taken up.
Do you give it deep soakings when you water?
There are other things it could possibly be, a bacteria or fungus perhaps, but I'd check on the water question first.