Question
Have grown these trees for landscaping for several years. Have noticed that one tree in a group has several dry branches and leaves. Is it dying or possible critters eating at the roots? Hope it does not spread to the other trees. Thank you

Answer
Hi Lindie,

If only one tree is affected and you see no abnormal symptoms on the other trees, it is possible that there is something chewing on the roots.  Usually, you can see evidence of an animal--tunnels, digging, etc, so be sure to take a close look.  

Aspens are troubled by many foliar leaf spots and canker diseases.  It is possible that what you are describing is the early symptoms of a canker problem.  The most common canker on quaking aspen is Cytospora canker and it generally results in death of the tree.  You will usually notice an unusual area on the bark (sunken, different color, broken) when the tree starts to decline.  The following website has pictures of the canker symptoms.  This may help you determine if the problem is simply caused by a pest or if there is a greater problem.
http://www.na.fs.fed.us/spfo/pubs/fidls/q_aspen/q_aspen.htm

Good luck!
--Jen