Selectivity and Fate of MSMA in Bermudagrass, Centipedegrass, and Seashore Paspalum

Centipedegrass [Eremochloa ophiuroides (Munro) Hack.] and seashore paspalum (Paspalum vaginatum Sw.) can be weedy species with other turfgrasses. Monosodium methylarsenate (MSMA) selectively controls these grasses in polyculture with tolerant species such as bermudagrass [Cynodon dactylon (L.) Pers.], but the mechanisms of selectivity are not well understood. The objectives of this research were to investigate the efficacy and behavior of MSMA in bermudagrass, centipedegrass, and seashore paspalum. In greenhouse experiments, the hierarchical rank of injury ranges for species from high to low was centipedegrass > seashore paspalum > bermudagrass. Monosodium methylarsenate reduced dry shoot biomass of centipedegrass and seashore paspalum six and three times greater than bermudagrass after 4 wk, respectively. The hierarchical rank of lipid peroxidation after MSMA treatments, as measured by malondialdehyde (MDA) content, from high to low was centipedegrass > seashore paspalum > bermudagrass. Grasses reached peak foliar absorption of ¹⁴C-MSMA at 1 d after treatment (DAT), but differences among species were not detected. There was no metabolism of ¹⁴C-MSMA in any species at 1, 3, or 7 DAT, suggesting MSMA could remain bioavailable in clippings of tolerant and susceptible grasses. Overall, the selectivity of MSMA in warm-season turfgrasses is associated with differential levels of lipid peroxidation.