I live in Port Coquitlam, BC. The trunk of my 4' tall Japanese Maple is damaged as shown in the photo. About 35% of the outer layer of bark is completely eaten near the ground. I don't know if it is due to a rodent eating the bark away, or damages caused by a severe winter. Should I apply prunning paint?
There was a really good article about bark damage in the last issue of Landscape Trades (January 2009 Vol31, No 1) magazine it might be good reading if you can get ahold of a copy. (try CNLA if you are interested as its a trade magazine not available in stores). As for the pruning paint generally the current practice is to not use a wound dressing for the damage you have shown. It may be caused by sun damage, cold damage or other mechanical injusry but it doesnt look like rodent damage to me.
Japanese maples are prone to fungal and bacterial infestations that can cause severe problems, even death. And they are quite touchy about drainage. Your specimen looks like it may be sitting low with higher soil around. If planted too deeply there may be a connection between this and the cankerous-looking damage to the main stem. Correcting the grade might help. Possibly also painting the damaged portions with a copper preparation (presumably sold for the purpose - I've never gone looking for it myself). As always, what to do depends on what, exactly is happening.
We do have copper products available here registered for use as fungicides. Copper oxychlorate and copper sulphate. Both available in powder form labelled for use as foliar treatments for a number of fungal issues on a number of host plants.
