Also called cockspurgrass or watergrass, this annual has upright, reddish purple stems that grow 1 to 4 feet tall. When mowed in lawns, the stems grow close to the ground. The large, smooth leaves are 1/4 to 1/2 inch wide. One plant may produce as many as a million seeds from July to September. The seeds fall to the soil, remain dormant over the winter, and sprout the following year in early summer. Barnyardgrass is a troublesome weed from mid-summer to mid-fall. It thrives in lawns, gardens, and unplanted areas with rich, moist soil.
Barnyardgrass is not usually a problem in lawns unless turf is weak, with open patches. Plants can be hand-pulled.