Yochino cherry tree dropping leaves

I have a yochino cherry tree that has dropped most of the leaves after they turned yellow. I had 2 of these planted last year and don't recall the tree losing so many leaves. The other y.c. tree has some yellow leaves and some have dropped but nothing like the other one. (both trees are probably 10 feet or so) I have watered both some, but not a lot. Could this be drought related? Can you give me a plan?

Thanks, S Adams

Anne's response:

From the description of the problems I think the problem is drought and heat related. Yoshinos do lose their leaves earlier than some other cherry trees and as many trees are this year they have gone into dormancy a bit early with the heat and drought of the summer. Hopefully we will have enough rain this winter for plants to recover. If we have adequate rain in February and March you should apply some fertilizer as the plants begin to open their blooms.