Question
When I moved into my home 8 years ago, there is this big cottonwood.  The roots are growing as much as 8" out of ground all over the yard, with a fungus growing on the roots.  One root is quite big, and having bad legs I seem to trip over it at all times, day or night.  Can I shave these roots to ground level, will it kill the tree?  I am using Orthonex sold to me by Home Depot, for the fungus. Any other suggestions?  Does not seem to be working to well.  Tahnk you

Answer
Shaving the roots will kill them.  I would cover the roots so they do not stick up above the ground level. Put sand just enough to cover not more than an inch or so above the root. If by a fungus you mean mushroom growing from the roots , this is the fruiting body of the fungus and applying a fungicide will not help. The fungus is inside the roots and there is not a way to treat this with a fungicide. The best way would be keep the tree healthy by fertilizing with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good.