Question
My 4 yr lilac has withering leaves and a section of dying? limbs. I found what looks like a brown hollow? caterpillar cocoon or tiny hive approx. 2 in by 1 in in diameter. Is it some type of insect or a disease, and what can I do to save my lilac? I have cut away the dying limbs, but do not know if it is spreading.

Answer
Becky:
From your description of this "cocoon", I suspect that this is indeed an insect, but probably not harmful to the tree, but just "hanging around" using the tree twigs for support.  If you wish, you can attach a photo and I will have a look.  Be sure to review your photo on your computer first- before sending to be sure it is in focus.  Try to get as close as you can to take the shot. Take a few and send along the best one.  

The wilting leaves and dying branches are probably caused by some other reason.  Take a look at the trunk of the plant and look for any evidence of loose/damaged bark just above the ground line. Also look for this situation on other portions of the tree. Has it been dry there? What about your watering schedule? Removing the dying limbs is OK.

Regards
Steve