Trunk Rot

Question:

 I have a large silver maple tree (probably 50 - 60 feet tall) that lost a major branch many years ago. This branch was about 8-9 feet off the ground and over the years a hole has developed in the trunk as moisture has softened/rotted the wood. What can be done to fill this hole and thereby avoid further weakening the tree trunk?

Minnesota Master Gardeners say:

 It is not recommended that the hole be filled with anything and the tree is probably already a hazard tree since rot is evident (caused by moisture and organisms). This is not uncommon with silver maples, which put on rapid growth and as a result have week wood which is subject to storm damage. Here is a brief which explains wood decay by fungi:
http://www.extension.umn.edu/yardandgarden/ygbriefs/P443wooddecay.html

A tree this size with rot in the main trunk can be a serious hazard. Here is some information from the publication FO-7415-GO Storm Damage to Landscape Trees: Prediction, Prevention, Treatment, http://www.extension.umn.edu/distribution/naturalresources/DD7415.html
on how to assess the strength of your tree:
Determining the extent of decay within the tree determines the tree's decay and potential to fail. There is a test for determining the strength loss within a branch or stem: for every 3 inches of branch or stem diameter, solid wood should comprise at least 1 to 1.5 inches. Anything less than that often indicates a branch or stem that is more likely to fail during a storm.

You may want to have an arborist assess the condition of your tree and perhaps handle the removal. The removal of damaged trees can be unpredictable, due to the unknown structural condition. Here is a brief about Hiring an Arborist which may help you: http://www.extension.umn.edu/yardandgarden/ygbriefs/p445arborist.html

If you want to attempt tree removal on your own, you can find information in this brief, Removing Trees and Shrubs: http://www.extension.umn.edu/yardandgarden/ygbriefs/h446removetree.html

Finally, if you opt to remove and replace the tree, you can use this SULIS search engine to help you find a tree which is appropriate for your site. You can enter search qualifiers like how much sun, or soil pH and soil drainage present at the site, and come up with a list of species. http://www.sustland.umn.edu/plant/search.asp It is best to plant a new tree at least six feet away from the central remains of the oldtree, if this is possible.