Things You'll Need
Japanese maple trees, when damaged, are susceptible to mold, fungus and boring insects. Protect the tree from excess moisture and bugs until the tree has time to heal. This takes a bit of time, since the bark doesn't grow that quickly, but if you maintain the healing process, you should see an improvement within a year. After healed, the tree will probably have a slight scar from the damage.
Pull off loose bark around the damaged area. If it is loose, it more than likely won't reattach, and will trap moisture underneath and develop mold.
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Apply a grafting wax to the damaged area to seal it from the elements and prevent mold. Spread the wax over the tree wound, making sure to coat the entire area. Coat the damaged area as well as up against the bark edges that surround it. You can use a spackle or your hand. Wear gloves if you use your hand.
Wrap the tree with a protection wrap for winter so that it isn't harmed by cold and frost. Tree wrap is a polypropylene fabric that protects trees against further damage. Place the end of the material up against the tree near the wound and hold it in place as you, or a helper, pulls the rest of the material around the tree and overlaps the end. Once around the tree once, and wrapped around its own end, the material will stay in place as you go around the tree several more times to ensure that you completely protect it from the elements.
If the wound is large, secure the material as mentioned and then continue to wrap at a slight angle so that you can move up the tree and cover the whole wound. Overlap the material so there are no gaps. Once done, cut the wrap from the rest of the roll and pull the end through the last layer to hold it in place.
Remove the wrap when the weather turns warm in the spring. Make sure that there won't be any more frosts before you take it off.
Spray the damaged area with a bug spray to keep insects from digging into the surface. Apply as recommended on the bug spray bottle. Not all sprays are the same, so read the instructions. Typically a few squirts is enough. Repeat the process as needed until the bark is healed. Weather will wash the spray away over time. Applying more every so often to protect the tree will not hurt it.