I hope you can help. We are in Wisconsin and enjoy the harvest of our fig tree, which was planted here at our shop by our father about 20 years ago. We just discovered that the large trunk is split and is actually rotting on the inside--on both sides. You can insert your hand and feel the softened insides. The tree appears to be quite healthy--dense leaf growth and producing a bumper crop! We go to great lengths for winter protection--yearly. Can we save this tree?
Fig Tree Concern
Certified GKH Gardening Expert
I would treat the hole with a fungicide to help slow the rot. Also, if you can, cover (do not plug) the hole to keep water out. Trees can live with holes in their heartwood without problems. As long as the bark and first green ring of wood (which is what keeps trees alive) is healthy, the tree will be fine.
Your only major concern will be that if too much of the heartwood rots, the branches may crack off. You can take steps, such as bolting the weakened branch, to help prevent this. This article will help:http://essmextension.tamu.edu/treecarekit/index.php/after-the-storm/tree-damage-and-hazard-assessment/repairing-storm-damaged-trees/
Read the section on split forks and this can be done for the tree before it actually splits. You can also call in an arborist to help with methods to prevent the tree splitting.