LAUSR

Greenhouse experiments were conducted in 2020 to investigate the effects of carrier volume and sethoxydim rate on torpedograss (Panicum repens L.) control and sand cordgrass (Spartina bakeri Merr.) response from a single application. P. repens control and biomass reductions generally increased with increasing sethoxydim rates in evaluations at 14, 28, and 42 days after treatment (DAT); however, increasing rate to 2X the maximum labeled rate did not always result in increased efficacy. In the first experimental run which consisted of small plants, P. repens control and biomass reductions were largely similar among tested carrier volumes (37, 187, and 935 L ha-1). However, in run two which consisted of larger, mature P. repens plants, efficacy increased when carrier volume was reduced. S. bakeri injury increased with sethoxydim rate reaching a maximum of 45% by 42 DAT. However, no differences in S. bakeri injury among carrier volumes were observed at 14 and 28 DAT evaluations. S. bakeri aboveground biomass reductions were also largely driven by sethoxydim rate increases rather than reduced carrier volumes reaching 40 to 50% reduction in initial aboveground biomass. However, S. bakeri belowground biomass was 20 to 32% greater in treatments applied at 37 or 187 L ha-1 compared to those at 935 L ha-1. Overall, these data suggest that selective P. repens control with sethoxydim may be enhanced through reducing carrier volumes from 935 L ha-1 and that native, perennial, caespitose grasses may exhibit greater tolerance to sethoxydim compared to the rhizomatous P. repens. Future research should further test these hypotheses under field conditions at operational scales.