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Filling Holes in Tree |
Question:
I have an old oak tree with a hole at the fork that squirrels live happily in. I'd like to block access, and I recently read in a garden magazine that holes in trees could be filled with the foam sealant used for insulation in houses-it would expand/contract with tree growth. Is this true? Can I use it without fear of harm to the tree? I am also planning to cut off a large dead limb. Is there anything I need to be aware of- sealing the spot, how close to cut to the tree, etc?
Minnesota Master Gardeners say:
Foam was tried as a tree hole filling but it doesn't work. Trees twist and bend a lot in ways not compatible with insulation foam. We recommend that it not be used.
Blocking access to that hole with any type of sealant will do two things. First, it will remove a natural nesting cavity for the squirrels and other woodland creatures. Second, the sealant will trap moisture and fungal organisms inside the tree. This sealed cavity near the branch union then becomes a place for rot fungi to grow. The resulting decay could eventually kill the tree. If the tree does not die, the internal decay will compromise the structure of tree resulting in a hazard tree.
A hazard tree is any defective tree, or tree part, that poses a high risk upon its failure or fracture to cause injury to people or damage to property. A hazard tree is one that has one or more defects which decreases its structural integrity and gives it an increased potential for failure. A defective tree is not considered hazardous unless there is a nearby target that it could hit. The target could be a sidewalk, a person, a vehicle, a building, a power line, and so on.
The following University of Minnesota fact sheet on Pruning Trees and Shrubs will provide the information needed to make a proper pruning cut on the dead branch:
http://www.extension.umn.edu/distribution/horticulture/DG0628.html Pay particular attention to Fig. 3 in the fact sheet as it illustrates how to make a proper and safe pruning cut.
When pruning or working around oaks, we must be aware of the potential for the spread of oak wilt disease. If your oak is pruned during the period July through March, there is no need to apply a wound dressing to the pruning cut. If the tree is pruned or wounded during the period April, May and June, the high risk period for the spread of oak wilt disease, apply a wound dressing immediately after pruning or wounding. Use either a water based latex paint or shellac.
If the branch that is to be removed is exceptionally large, or if you must mount a ladder to get access to the pruning site, you might consider using the services of an arborist certified by the International Society of Arborists. The following web site lists certified arborists in Minnesota: http://www.isa-msa.org/