Question
What can I do about bare spots in my lawn?  I think it  
may be from tree roots.

Answer
Hi Don, Proper soil preparation is the key.  The soil under a tree is very competitive real estate.  The competition for food and water in conjunction with shade makes it very difficult for grass to survive.  Loosen the soil as deep as you can (4-6 inches if possible). Check your pH, it should be 6 to 6.5.  During the summer months, water deeply when you need to water.  A sprinkler should run twice a week for 2 hours in the same spot to deep water if your soil is clay.  When you get ready to seed or sod, check with your local garden center for the best shade and drought tolerant grass for your area.
Lawn grasses are sun plants, some tolerate shade, but you never see grass in the forest so even with the best care, you may need to re-seed some each year.  Left to it's own over time, the area under trees becomes a woodland garden...consider this as an opportunity, instead of a challenge. Jim