Regarding your question about your ornamental cherry dropping leaves suddenly; with out seeing the tree or knowing more about how much water your sprinklers are supplying I can only venture a guess.  It is a distinct possibility that the tree may be getting too much water from the sprinkling system.  Cherry trees especially don’t like to have “wet feet”.  And in heavy clay soils (which are typical) the water tends to hang around for extended periods of time.  A good indication of whether this is the issue, dig down next to the tree and observe the soil conditions.  If it is sticky and mucky you know it is too much water.  You may also get a musty smell indicating the presence of rotting organisms.  Once the roots rot away the tree has no way of getting water up to the leaves, this can cause the tree to drop the leaves.  Another thing to look for are circling roots that can “choke” the tree and or the tree being buried too deep.  When a tree is planted too deep, the soil around the trunk will rot the conductive tissues away which will also prevent the conductive tissues from supplying water to the leaves.