Poke around in the soil to check.

I've done that. The soil is dry. However I have watered it 4 times in the past two weeks. Soil drys out rather quickly. Was hoping someone could tell by the leaves.

And the other 4 trees seem to be doing fine. While watered the same amount.

are the others planted way to close to the fence like this one.. with too much heavy rock on top of the soil also ....

could the fence be generating more heat form the sun because its in a corner.. or something or other....

water when a plant needs water ... check your soil.. and if its dry.. then water more ...

there is no rule in the universe.. that every duplicate plant in your garden is exactly the same .. so treat them each as each needs ...

its called micro climates ... and it can vary across a very small area. and include.. soil.. drainage.. wind.. sun ... shade ....... and every other pertinent cultural variable ...

ken