My Chisese Elm is dropping it's leaves?

Question:It's summer here, and my 3 chinese elm trees are dropping their leaves like crazy. And 2 of my tree's bark is flaking off. Are they sick?

(they have been in the ground for about 2 years. and are watered by irrigation atleast once a month.)

Answers:
sorry--I don't like chinese elms. my neighbour behind me has a huge chinese elm that I cuss at every time it drops 3 inches if those dang seeds in my back yard. just finished scooping elm seeds out of my veggie garden yesterday. have to scoop em up cuz they sprout so frikkin easy.