Physiological Basis for Bermudagrass Control with Ethofumesate in Seashore Paspalum and St. Augustinegrass

Bermudagrass is a problematic weed in seashore paspalum and St. Augustinegrass with limited options for control. Ethofumesate is the only herbicide labeled for bermudagrass control in these turfgrasses, but the physiological basis for selectivity is not well understood. The objectives of this research were to evaluate the efficacy and fate of ethofumesate in bermudagrass, seashore paspalum, and St. Augustinegrass. In the greenhouse, ethofumesate rate that reduced shoot biomass 50% from the nontreated plants was 3.8, >27, and >27 kg a.i. ha‐1 for bermudagrass, seashore paspalum, and St. Augustinegrass, respectively. In the laboratory, absorption of 14C‐ethofumesate ranked bermudagrass > seashore paspalum > St. Augustinegrass from root uptake, and bermudagrass > seashore paspalum = St. Augustinegrass from foliar uptake. St. Augustinegrass translocated ∼20% less of the total absorbed radioactivity to shoots than the other grasses after root uptake. Metabolism of 14C‐ethofumesate ranked bermudagrass > St. Augustinegrass > seashore paspalum. All grasses metabolized the herbicide to ethofumesate‐2‐keto, methanesulfonic acid, and another polar metabolite. Of all grasses, seashore paspalum produced the highest and lowest levels of ethofumeaste‐2‐keto and methanesulfonic acid, respectively. Radioactivity recovery linearly decreased by 81 to 35% of the applied 14C, from 1 to 7 days after treatment, suggesting volatilization is a major contributor to ethofumesate losses. The susceptibility of bermudagrass to ethofumesate results from greater absorption than seashore paspalum and St. Augustinegrass. The intermediate tolerance of seashore paspalum to ethofumesate results from root absorption rather than foliar uptake. Metabolism rate does not appear to be correlated with tolerance levels of these species to ethofumesate.