14 C‐Trinexapac‐Ethyl Absorption and Translocation in Kentucky Bluegrass

Trinexapac‐ethyl [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxocyclohexanecarboxylic acid ethyle ster] is a foliar‐applied growth regulator for turfgrass that can reduce mowing frequency, clipping production, and enhance turfgrass color. 14 C‐Trinexapac‐ethyl was used to evaluate absorption and subsequent 14 C‐trinexapac‐ethyl translocation in hydroponically grown ‘Blacksburg’ Kentucky bluegrass ( Poa pratensis L.). The magnitude and rate of 14 C trinexapacethyl absorption by various organs was as follows: plant base > leaf blade > roots. Plant base, as a morphological description and site of application, refers to the collection of leaf sheaths surrounding the compressed turfgrass stem and the crown of the plant. Over the time period of 0 to 24 h, maximum absorption by the plant base was obtained in 8 h and by the leaf blade in 24 h. Absorption by the roots was negligible. Addition of an activator organosilicone abjuvant, Sylgard 309, significantly enhanced 14 C‐trinexapac‐ethyl absorption by the leaf blade 1 h after application but did not enhance absorption by the plant base. Of the 14 C‐trinexapac‐ethyl absorbed dy the plant base, over 50% was translocated to the plant foliage after 24 h. Of the 14 C‐trinexapac‐ethyl absorbed by the leaf blade, one‐third was translocated after 24 h; the direction of movement was predominantly basipetal.Less than 5% of absorbed 14 C‐trinexapac‐ethyl from either site was translocated to roots or to rhizomes with daughter plants, explaining the lack of inhibition of lateral turfgrass growth. Combined effects of enhanced leaf blade absorption, basipetal translocation from the leaf blade, and acropetal translocation from the plant base of 14 C‐trinexapac‐ethyl helped explain the positive impact of Sylgard 309 on efficacy and rainfastness of trinexapac‐ethyl.