Green foxtail

Green foxtail (Setaria viridis) is a warm-season summer annual forming upright to spreading clumps, generally finer and smaller than giant foxtail. Its seedhead is a dense, bristly, cigar-shaped spike that is upright to slightly nodding, with green bristles that may age to tan. The key identifier is the leaf blade: it is essentially smooth and hairless on both surfaces, which separates green foxtail from yellow foxtail (long silky hairs at the leaf base) and giant foxtail (short hairs over the whole upper blade surface). Stems are slender and the sheath margins are typically hairy.

Green foxtail forms coarse, fast-growing clumps that contrast in texture and color with finer turfgrass, and its bristly green seedheads rise above the mown surface in mid to late summer to give a weedy appearance. The bunch-type clumps compete with thin turf for light, water, and nutrients during summer, emphasize bare and weak areas, and shed abundant seed when the annual plants die at season's end, setting up reinfestation the following year.

Green foxtail is a summer annual reproducing solely by seed and completing its life cycle in one season. Seeds germinate as soils warm from mid-spring into early summer, plants grow through summer, set seed from roughly July through September, and die at season's end, leaving seed in the soil to germinate the following year.

Green foxtail invades thin, open, low-maintenance turf and disturbed or newly seeded sites, filling gaps during the summer when cool-season turf may thin under heat and drought. Dense, healthy turf resists it, so it is most problematic where turf vigor and density are low or where soil has been recently disturbed.