In the picture it looks a lighter color than I usually see it but it looks like Polygonum persicaria L.,
Ladys thumb, Spotted ladysthumb

Might be swamp smartweed, a close relative of lady's thumb. Regards, Peter.

Looks like Pennsylvania smartweed -- does it have little spire of pink-purple flowers? It's a common roadside wildflower that's a weed when it's in the yard. It can get pretty big from a single root, but it pulls right up, root and all, after a rain. Get it before the flowers go to seed. Good luck. Alex