That tree is suffering from some type of root problem. Dry soil or soggy soil are both possibilities. Try digging down a few inches to feel the soil and see what you think. If the damage from moisture extremes was not to severe the tree may recover with proper soil moisture maintenance.
Another possibility is damage from a week killer or even from certain broadleaf weed and feed products applied near the tree. When these products are overapplied and then it rains or you irrigate to wash them down into the soil tree roots may be affected. Time is the only solution to herbicide injury.
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