Easy to spot, not so easy to kill. My property backs to a small river and the adjacent floodplain is overrun with buckthorn.

I’ve attempted to kill a few trees that have grown near my house; cut the tree down, paint the stump with triclopyr. At first it seems to work, but the next spring, a dozen new stems are starting from the base. It becomes overwhelming. Nasty stuff.

And yep, the leaves are still on here in SE Michigan (although with the recent snow, they may not be for long).