When I saw this today, I knew what it was because I've seen it before. Tree looked green but just laying over on its side. I've had it happen to oaks too.
Also found a Norway Spruce that had been done the same way - first one of those I had seen.
That's for sure. It's hard to apply protection below the ground. The good news is that I now have about 25 or more chestnuts that are large and have been producing for a few years. Hopefully those are home free. It's interesting that I've never had a pear or apple gnawed below ground level, but have heard of other folks that have had it happen.
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"Somebody told me last fall to put moth balls in the cages with tiny nut trees so the field mice/voles wouldn't eat them. I am happy to report that when I went to check on one and replace its stinky little guardians, it is hale and hearty, completely unnibbled."