A mature oak in my yard, and another in the neighbor's, has what I think are armillaria mellea growths around the trunk and roots. What is the best way to treat this? Reading on the internet, it seems that removing the fungus (with a shovel and saw?) is the best way. Should I be cutting away at the roots and trunk at all, or just getting the fungus off? Any other guidance?
There really is no treatment or cure for Armillaria rot. Don't cut into the roots or trunk. Anything you can do to maintain the health of trees (watering, proper pruning, avoiding physical injury) is really the best you can do. When trees are stressed, they become more susceptible to this fungus and decay. Trees can survive for a while with Armillaria, but it is a symptom that they are in decline and you might want to consider removal.