Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin oryzalin, imazapic, imazapic 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin oryzalin and imazapic 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control.
Nomenclature: Asulam; benefin; CGA 362622, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide; 2,4-D; imazapic; imazaquin; oryzalin; blanket crabgrass, Digitaria serotina (Walt.) Michx. #3 DIGSO; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; St. Augustinegrass, Stenotaphrum secondatum (Walt.) Kuntz; torpedograss, Panicum repens L. # PANRE; tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster # BRASU.
Additional index words: BRASU, DIGLO, DIGSO, PANRE.
Abbreviation: WAA, weeks after application.
