Rotten wood in basswood tree.
40 year old 15 in DBH Basswood. Has sunscald on SW side 5 ft above ground. Area is about 15 in tall and about 6 in wide in middle tapering to ends. There is damp rotten wood which can be pulled out. Tree appears to be very healthy. What should be done with it?
1. Remove the rotten wood?
2. After removing, spray the cavity with a fungicide?
3. Fill the cavity?
4 Do nothing
Without a diagnosis and evaluation of the tree, we can't suggest a simple plan of action except to say that The University doesn't recommend using any chemical product unless you know what the problem is you are trying to treat, and we don't advise filling a cavity or removing debris because this can cause more trouble for the tree. This article describes tree cavities and some do's and don'ts: http://hort.ifas.ufl.edu/woody/cavity.shtml
The University of Minnesota has a self diagnostic tool that might help you diagnose the problem and decide upon a course of action: http://www.extension.umn.edu/garden/diagnose/plant/deciduous/linden/
Basswood aren't terribly long lived trees and their wood is soft. It's not unusual for the older trees to be rotten and hollow inside. If the tree is rotten and a danger to property or people, it should be removed.