Carpetweed
Mollugo verticillata
Annual; spreads by seeds; stems grow to 1 foot; found across U.S., except for ND and parts of MT and MN; flowers June through November.
Hoe or pull plants when they appear. Mulch deeply to smother any seedlings.
Photo: (cc) Robert H. Mohlenbrock/USDA
Large Crabgrass
Digitaria sanguinalis
Annual; spreads by seeds/roots at leaf joints; height to 3 feet; found across U.S., except ND and parts of SD, MT, and MN; flowers June through October.
Pull out entire plant, including roots. Mulch or let grass grow to 3 to 4 inches high to prevent seed germination. Mowing will not kill this plant. Spread corn gluten in early spring to suppress seedlings.
Photo: Rodale