Question
I have a few seperately planted Quaking Aspen trees of about 3-4 years.  This spring when they developed their leaves a few of them have drooped significantly from about midway up.  They almost look as if they will fall over. I've heard of something called drooping aspen disease. Could this be the problem, and is there a remedy?

Answer
The following link is a pretty good synopsis of quaking aspen tree culture and associated problems.  Sounds like they may have a canker disease in the trunk.  Otherwise they may have just put on a lot of new growth this spring and with the onset of hot weather, are not able to hold all of the foliage they have put on.  I am from Mississippi, so I have little knowledge of aspen culture.  I would call your local county cooperative extension office and see if they can provide better assistance.

http://www.colostate.edu/Dept/CoopExt/4dmg/Trees/aspencan.htm

Good Luck.