what is this plant
This is Canadian clearweed: http://www.marylandbiodiversity.com/viewSpecies.php?species=2686
It is a native annual and is fine in your woods, but it can be a nuisance in ornamental beds. Easy to pull. Don't really need to use an herbicide. They are so tender, you might be able to just walk on and crush those seedlings when they're little. Just don't let any of those seedlings survive and produce more seeds. They produce tons of seeds and they can do it at a young age.