Tropical Signalgrass Control in Seashore Paspalum

Abstract

Tropical signalgrass (Urochloa subquadripara) is a mat-forming grass with relatively coarse texture. It is characterized by hairy sheaths and leaf blades plus a short fringe of hair present on the ligule. Tropical signalgrass control in Florida has been challenging for turf managers, in part, due to monosodium methanearsonate (MSMA) restrictions. Previous research indicates fall herbicide applications to be more effective than summer applications; however, fall applications typically do not allow turfgrass adequate time to fill in bare spots prior to winter. Two studies were conducted on seashore paspalum (Paspalum vaginatum) roughs at The Oaks golf course in Osprey, FL in summer 2019 comparing single and combination treatments of amicarbazone, carfentrazoneethyl, sulfentrazone, flazasulfuron, and quinclorac for control of tropical signalgrass. All treatments were applied with a non-ionicsurfactant at 0.25% v/v. In both studies a sequential application of each treatment was made 21 days after initial treatment (DAIT). Rating dates were 4 June, 25 June, 16 July, and 13 August, corresponding to 0, 21, 42, and 70 DAIT, respectively. In study one, 10 weeks after initial treatment (WAIT), amicarbazone + carfentrazone-ethyl + sulfentrazone at 0.23 + 0.0076 + 0.068 lb ai/acre (0.26 + 0.0085 + 0.076 kg ai/ha), respectively, provided best control (~60%). For study two, at 6 and 10 WAIT, tropical signalgrass control of >50% was not achieved. Overall, long-term postemergence control of tropical signalgrass with summer applications of herbicides tested was incomplete, even with multiple applications; however, amicarbazone + carfentrazone-ethyl + sulfentrazone showed potential as a control option.