Also known as cheeseweed (thanks to the fruits, which resemble a round of cheese), common mallow is a widespread annual or biennial weed with broad, lobed leaves and pinkish white, five-petaled flowers.
Hoe or pull these weeds when they're young. Mature plants have a long, tough taproot that is difficult to extract from the soil, and they are of course more likely to have set seed.
For chemical control, use a pre-emergence herbicide containing isoxaben to prevent seedlings from becoming established in lawns and around ornamentals. For post-emergence control in lawns, use a product containing MCPA, MCPP, and dicamba. Spot-treat young weeds with an herbicide containing glufosinate-ammonium or glyphosate, taking care to avoid contact with desirable plants.