Physiological Behavior of Ethephon in Five Turfgrasses

Turfgrass seedhead emergence often warrants plant growth regulator (PGR) use for suppression, but practitioners have limited chemistries available for warm‐season species. Ethephon effectively suppresses turfgrass seedheads, but injury to bermudagrass and seashore paspalum is often excessive. Experiments were conducted to evaluate differential behavior of ethephon in bermudagrass and seashore paspalum, compared with annual bluegrass, creeping bentgrass, and zoysiagrass. In greenhouse experiments, ethephon was most injurious to bermudagrass and seashore paspalum, ranging 19 to 40% from 3 to 28 d after treatment (DAT), while annual bluegrass, creeping bentgrass, and zoysiagrass had less injury, ranging 9 to 21%, across three application rates (1.9, 3.8, or 7.6 kg a.i. ha –1 ). In laboratory experiments, foliar absorption of 14 C‐ethephon generally increased from 24 to 96 h after treatment (HAT), but differences among species were not detected. Creeping bentgrass and zoysiagrass retained >90% of foliar applied 14 C in treated leaves, but bermudagrass and seashore paspalum distributed ∼25% more 14 C to nontreated shoots. From root absorption, bermudagrass and seashore paspalum distributed ∼25% less 14 C to shoots than creeping bentgrass at 72 HAT. Annual bluegrass 14 C distribution after foliar and root absorption was similar to all species, except creeping bentgrass. There were no meaningful differences in turfgrass metabolism levels of 14 C‐ethephon at 1, 4, or 7 DAT. Results suggest differential levels of distribution after root and shoot absorption could be associated with bermudagrass and seashore paspalum sensitivity to ethephon compared with turfgrasses with less injury potential.