[Mrs. Don-o]

Hard for me to tell from the picture --- you need a close-up of the leaves and/or a fairly detailed indication of its growth habit. if those leaves areheart-shaped, with a little crease downthe biddle, I'd guess yellow woodsorrel.

http://tinyurl.com/yellow-woodsorrel A broadleaf herbicide if you want to kill everything but your grass. RoundUp of you want to kill everything....

Or you could try goats.

[Mrs. Don-o]

Oops. I meant “a little crease down the middle.”