Rot discovered in Birch tree - Bronze Birch Borer ?

I have a white birch (I assume it's a paper birch) that's basically 2 big trunks that are joined at ground level and diverge and each trunk rises to a hight of about 30 ft. Diameter of each at ground level is probably a foot or slighty more. Tree (both of them) seem healthy, leaves are fine. For the past 3 or 4 springs I've applied Cygon around a section of both trunks.
Last year I noticed just under the crotch of one of the major branches some weakness in the bark. What I found when I peeled off the bark was several fluid-filled cavities (each about the size of a silver doller). I basically peeled away the bark over these cavities and exposed them. The cavities seemed to reach all the way to the dead-wood of the trunk (about 1/2 inch deep). If I recall correctly, a bunch of ear wigs probably fell out of these cavities.
This spring I examined the same trunk but lower down and there was a similar weakness or spongy-ness to a section of bark closer to the ground. Today I finally went about opening up this abscess. What I have is basically a gash in the side of the trunk that has been completely masked by the thin outer layers of paper bark. This gash starts about 5 ft from the ground and goes up about 4 feet long. On average it's about 2 or 3 inches wide, but could be 4 inches wide in places. The gash goes all the way to the wood core of the trunk (ie the gash is about 1/2 deep). I can see a few worm trails in the exposed hard wood core so I assume that some sort of borer did this.
Bur what I understand about the bronze birch borer is that they usually attack higher up the tree. Also, is it common for a verticle section to be eaten out vs going around the trunk?
Once I cleaned up the gash by cutting out the bits of dry rot I think that the trunk will heal ok (heck - this gash has been there for must be years). I figure that exposing this gash to the outside will allow it to harden up (and it won't be home for ear wigs any more - yuk).
What I'd like to know is
1) Was this the Bronze birch borer?
2) Is there a filler material for trees that's sort of like bondo (for car body work)? I'd like to fill this gash with something that I can at least paint white so the tree doesn't look so bad.
PS: I'm located in SW Ontario so my climate is similar to Detroit, Cleveland, and Buffalo. Also, please post any follow - up (don't e-mail because I won't get it).
Thanks.
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BBB is a Buprestid beetle that attacks woody tissues. It is part of the cosmological dance. Don't fill the new excavations with anything. It won't benefit the tree.
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Mike LaMana, MS
Heartwood Consulting Services, LLC
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Mike LaMana wrote:

So you woulnd't recommend products like this:
Treekote Tree Wound Dressing http://www.forestry-suppliers.com/product_pages/view_catalog_page.asp?id 68
even if only to improve the appearance of the trunk?
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No, I don't see the need.
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Mike LaMana, MS
Heartwood Consulting Services, LLC
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I may be mistaken, but these borers will make a hemispherical hole in the trunk or branches. Look for them. If you find them, I believe Lindane one of the treatments for borers..
Sherwin Dubren
Some Guy wrote:

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Sounds more like a canker disease
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Beecrofter wrote:

I assume that this web site describes what you are referring to:
http://www.pfc.forestry.ca/diseases/CTD/Group/Canker/canker6_e.html
That doesn't look like what I have.
Basically, I had a complete dissappearance of the wood (sap wood?) in a uniform manner all the way to the wood core, where there are quite prominent worm trails etched in the surface of the core (heart-wood?). This gash or dissappearence was completely hidden under the outer surface of bark (which was 1/8 inch to 1/4 inch thick). The outer bark surface was COMPLETELY NORMAL LOOKING and you wouldn't know that something really wrong was going on underneath. There were no holes in this over-covering section of bark nor anywhere else I've looked. No fruiting bodies in the 5 years I've been the owner of this tree.
The cavity formed by this gash was moist and in places seemed to retain fluid. The sides of the gash resembled a thin layer of dry rot (probably due to water retention and lack of air circulation). I scraped away the thin layer of rot and exposed what looked like healthy sap wood. I expect the exposed sap wood will harden relatively quickly.
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