Sourgrass is a stoloniferous perennial grassy weed found on golf courses throughout Hawaii. No herbicides are currently labeled for selective control of sourgrass in seashore paspalum turf, a species used regularly on golf courses throughout the tropics. A single granular application of fine salt (99% sodium chloride, 1% sodium silicoaluminate, 83% of particles 0.5 to 0.25 mm in diameter) at a rate of 1,464 kg/ha provided 84 and 23% control of sourgrass 6 wk after initial treatment (WAIT) in 2007 and 2008, respectively. Sequential granular applications of fine salt at 488 kg/ha provided 92 and 96% control of sourgrass in 2007 and 2008, respectively, at 6 WAIT. Granular applications of a coarse salt (100% sodium chloride, 75% of particles 2.0 to 1.0 mm in diameter) provided a lower level of control than fine salt at both the 1,464- and 488-kg/ha rates on three out of four rating dates in 2008; a similar trend was observed in 2007, but no significant differences were observed between these treatments. All salt treatments led to higher soil sodium adsorption ratios (SAR) and electrical conductivity (ECe) than the untreated check; however, levels reported in this study were significantly lower than the threshold SAR and ECe levels that have been associated with reduced seashore paspalum growth. Sequential applications of MSMA at 1.12 kg/ha and MSMA plus metribuzin at 1.12 kg/ha and 0.28 kg/ha, respectively, provided greater than 90% control in 2008, but less than 40% control in 2007. Greater seashore paspalum injury was observed following applications of MSMA and MSMA plus metribuzin than following salt applications. Additional research is needed to evaluate strategies for controlling sourgrass in seashore paspalum turf that do not induce phytotoxic injury after application.
Nomenclature: Metribuzin; MSMA; sourgrass, Paspalum conjugatum Berg. PASCO; seashore paspalum, Paspalum vaginatum Swartz. PASVA.