Question: I went and looked at a pecan tree that this man had on his property. There was a fungus growing around the entire base. The color of the fungus was brown (rusty) on top with white on the bottom. It is about an inch thick and very firm (like styrofoam) He swears it is killing his tree. Can you help me.

Answer: This appears to be a Ganoderma fungus (I don't know which species) capable of causing a butt rot of pecan and other hardwood trees. Some photos are available at this site for comparison with your client's pecan tree:

http://www.invasive.org/browse/subimages.cfm?sub=517

Risk factors for Ganoderma butt rot are injury (digging for utilities, sprinkler system, mower and string-weeder damage), drastic change of grade during site preparation/landscaping, drought stress, excess moisture/poor drainage, etc. Injury combined with drought stress are probably the biggest risk factors. The worst situation I've seen was around a residence on a steep gravely ridge with rapid internal soil drainage where every shrub and tree had significant mower/string-weeder damage; live oak, Texas persimmon, and other trees were affected). Ganoderma is usually slow acting, so the infection may have started several years ago.

If the tree canopy is thinning, the tree may have to be removed sometime in the future (before dead limbs begin falling).