The mistletoe clings to the tree at multiple places, so if you just cut the stuff at one or two spots. like you'd do with a rifle, it still ain't gonna fall down out of the tree.

And any damned fool that should be allowed close to a gun knows you don't shoot solid slugs UP unless there's somethin' up there shootin' down at you. Even a .22 can go downrange quite a bit over a mile, and you can't know for sure what's downrange no matter how "unpopulated" it is.

You want to use the smallest shot that will tear up a sizeable part of the mistletoee, to minimize damage to the tree, and a choke that will give you a "spread" at the range to the 'toe that's about half the size of the clump you're trying to get down, or maybe just a little more "open."

Muzzle velocity is pretty much the same for any shotgun, so a bigger bore just lets you get more pellets of a given size up in each shot with a bigger gun. Two shots from a .410 will give you about the same effect (same number of pellets) as one from a 12 ga. Smaller shot gives you more hits, if the pellets are heavy enough to break something where they hit, and all you've got to do is rip the 'toe tendrils loose. I'd guess that about #6 shot should be heavy enough, but you might put a couple of #4s in your pocket in case three or four shots (with your .410) with the smaller stuff doesn't get results.

At 60 to 80 feet, #6 shot only goes about 3 inches into a quail or pheasant, and each pellet that hits the tree at that range is only likely to go around a half inch or an inch at most into the wood, and is about like driving a 10 penny nail in far enough to hang granny's picture on, so it shouldn't hurt the tree all that much. A #4 pellet is more like a 12 penny nail. At close range where the bunch of pellets all hit close together, you might "bark" the tree and injure it, but reasonable range, decent aim, and a smart choice of shot sizes should be safe enough (for the tree). You may knock a few small branches (pencil size?) out of the three, but that's not going to hurt a mature tree much.

John