Question
the silver maple in my yard is abut 70 years old and ailing.  i live in upstate new york.  an arborist with whom i have consulted is suggesting routing out trunk rot in the crotch of the tree and stuffing it with foam in addition to pruning dead limbs and deep root fertilization in order to prolong the life of this lovely tree.

does stuffing the tree with foam make sense to you?  any other thoughts are appreciated.  thank you.

Answer
I would not recommend trying to cut out the rotten wood and apply the foam. In the first place you can not get all the wood cells that the decay fungi is in out. The decay will go deep down into the trunk and even up in the trunk. Then if the foam is added it will hold the moisture in and allow the fungi a great environment to grow. Fungi need moisture. warmth and food to grow. Eliminate any of these and the fungi will die. The tree can live many years with the trunk hollow. There is enough good wood around the decay that can support the tree. The fungi will not kill the tree it weakens the trunk strength and could lead to breakage. Usually you will see large limbs break first and they will be decayed where they were attached to the trunk.

Pruning off the dead limbs is a good idea- it will make the tree look better. And fertilizing is also good- it will increase the overall health of the tree. After they deep fertilize this time, I would apply 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Apply just before a rain storm and you will not need to water. Apply this fertilizer next Fall and this will increase the root production and in turn the foliage. The fertilizer will help the health of this tree a great deal.  

Prune Only the dead limbs and No live limbs. You need the foliage to product a good roots growth and growth of cells around the decay area.