I live in a wooded area. Have a large white Oak( 100ft+) within 10 ft. of house. The the Oak has 2 major sections out of the ground; one side is doing better than the other, want to know if by fertilizing an old tree like this I can improve the roots to better stabalize the tree. One site was selling Fertilizer for oaks, also Mycorrhizal fungi, is this the way to go and will this help an old tree? Thanks for your help.

Mark, It is questionable whether fertilizer or myc will help an old tree. Unfortunately damage often occurs during contruction. Your best bet now is to try to reduce any stress such as no grass under tree and no further compaction. You may want to check with your local Extension for info specific to your area. http://extension.caes.uga.edu/