I suppose she should figure out what it is and spray it. My theory is obviously its something that eats maple wood. While it no doubt is natural and is helping the stump decay if it gets in a wound on the other tree it may start doing the same thing.

Is this a more natural grove of trees where we should let nature take its course? Stumps interest me more than a dead cemetery or golf course like yard but I understand if the other maple is the pride and joy of the front yard you have to protect it.

Don't know if the previous post was tongue-in-cheek or not. But don't spray.

I was rather gritting my teeth when I suggested killing whatever fungus or ???? was eating that trunk.

I'm somewhat a naturalist but was trying to find a middle ground.

Well, there is only one other maple in the yard. It is her favorite tree, though, so I know she'd like it to live. I would guess it is about twenty yards from the diseased stump.

So... just let it go? Thank you for the advice.

to help the stump decompose quicker, dig out some of the soil around the base of the stump, about a foot out and a few inches deep. then cover the stump with fresh manure (cow, horse or chicken). if there are no farms near your area, goto homedepot or lowes or other home improvement stores and buy a couple of bags of composted cow manure. keep it moist. you can also cover with a large plastic bag. the heat, moisture, and nitrogen will quickly decompose that stump.