Absorption, Translocation, and Metabolism of Prohexadione Calcium in Annual Bluegrass (Poa annua), and Three Turfgrass Species.
M. J. Goddard, Josh B. Beam, and Shawn D. Askew. Virginia Tech, Glade Road Research Facility, 435 Old Glade Rd., Blacksburg, VA 24061-0330
Prohexadione calcium is an experimental turfgrass growth regulator that selectively controls or suppresses annual bluegrass in desirable turfgrass such as creeping bentgrass (Agrostis stolonifera, Kentucky bluegrass (Poa pratensis), and perennial ryegrass (Lolium perenne). To help explain interspecific differences in turfgrass and weed response to prohexadione Ca, two laboratory trials were conducted to measure 14C-prohexadione Ca absorption, translocation, and metabolism in these four species. Annual bluegrass, 'Penncross' creeping bentgrass, 'Prosport' perennial ryegrass, and 'Kelly' Kentucky bluegrass were transplanted from field grown plants thinned to one tiller and one fully expanded leaf and placed in 0.25% Hoagland solution in the greenhouse with average nighttime and daytime temperatures of 20 and 30 C, respectively. Plants acclimated for 1 week before treatment. Foliar absorption and translocation were determined by applying three 1-ƒÝl droplets of treatment solution to the newest fully expanded leaf blade on each plant. Annual and Kentucky bluegrass absorbed more prohexadione Ca than creeping bentgrass and perennial ryegrass when averaged over harvest timing and trial. Neither translocation out of the treated leaf or metabolism of prohexadione Ca differed between species. When averaged over species and trial, 22% of recovered prohexadione Ca was metabolized within 1 HAT, and plants metabolized an additional 0.7% each additional hour for a period of 48 hours. Previous research indicates that annual and Kentucky bluegrass growth is suppressed more by prohexadione Ca than creeping bentgrass and perennial ryegrass. Increased prohexadione Ca absorption partially explained this trend in the current study.