Plants annual. Culms 50-200 cm. Sheaths glabrous, fringed with white hairs; ligules about 2 mm; blades 15-30 cm long, 10-20 mm wide, usually with soft hairs on the adaxial surface. Panicles 6-20 cm, densely spicate, arching and drooping from near the base; rachises densely villous; bristles (1)3(6), about 10 mm. Spikelets 2.5-3 mm. Lower glumes about 1 mm, acute, 3-veined; upper glumes about 2.2 mm, obtuse, 5-veined; lower lemmas about 2.8 mm, obtuse; lower paleas about 2/3 as long as the lower lemmas; upper lemmas pale, finely and distinctly transversely rugose; upper paleas similar to the upper lemmas. 2n = 36.
Setaria faberi spread rapidly throughout the North American corn belt after being accidentally introduced from China in the 1920s. It has become a major nuisance in corn and bean fields of the midwestern United States.