Fate of Prohexadione Calcium in Annual Bluegrass (Poa annua) and Three Turfgrasses

Abstract

Prohexadione calcium is an experimental turfgrass growth regulator that selectively controls or suppresses annual bluegrass in desirable turfgrass such as creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. To help explain interspecific differences in turfgrass and weed response to prohexadione calcium, two laboratory trials were conducted to measure 14C-prohexadione calcium absorption, translocation, and metabolism in these four species. Annual and Kentucky bluegrass absorbed more prohexadione calcium than creeping bentgrass and perennial ryegrass when averaged over harvest timing and trial. Radioactivity partitioning to other foliage did not differ between species but annual bluegrass and Kentucky bluegrass translocated more radioactivity to roots and evolved more radioactive CO2 than creeping bentgrass and perennial ryegrass. Thin-layer chromatographic separations indicate radioactivity was translocated predominately as prohexadione calcium. When averaged over species and trial, 25 and 16% of recovered prohexadione calcium was metabolized within 1 h after treatment in treated leaves and other foliage, respectively. The rate of metabolic degradation was 0.7% h−1 in treated leaves and 0.4% h−1 in other foliage. Previous research indicates that annual and Kentucky bluegrass growth is suppressed more by prohexadione calcium than is growth of creeping bentgrass and perennial ryegrass. Increased prohexadione calcium absorption partially explained these interspecific differences in growth suppression.