how to eliminate mallow weed
From your photo, this appears to be oxalis, or yellow woodsorrel. Here is information on that from our website's weed section: http://extension.umd.edu/hgic/oxalis-yellow-woodsorrel
We don't see any grass in this photo. Once a lawn reaches less than 50% turf, it's recommended to start over, by killing all weeds and turf and reseeding. It's not worth it to simply kill weeds because grass cannot fill in the empty space created by the dead weeds faster than new weeds can. Here is a very good publication about seeding from our website: http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG102%20Lawn%20Estab...