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
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.
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).