I have a weeping hemlock that suddenly started to lose all of its needles.  The needles did not turn brown before falling off & the ground is covered with green needles.  Prior to this, it seemed to be thriving with lots of new growth.  Within a matter of two days it has lost almost all of its needles.  I don't see any obvious signs of bugs.  Any ideas what could be wrong??

Kalilahi, perhaps your soil type, hemlocks like acid soil.

The soil could be problem since we live in an area that is basically all clay.  I haven't seen any evidence of the woolie bugs- no egg sacs etc.  The needles don't appear to be damaged either, they are just all falling off.  I am going to hold out for a while before replacing the tree.  Although the needles have fallen, the branches themselves appear to still have life.

Thanks!

Is there any chance you have the wrong name? Tamarack shed their needles in the fall, but usually turn brilliant orange in doing so. I would take a branch in to a certified hortoculturist and see if they can help you. Many nurseries and larger garden areas in hardware stores often hire a certified horticulturist.