14C-trinexapac-ethyl absorption and translocation in Kentucky bluegrass

Trinexapac-ethyl [4-(cyclopropyl-alpha-hydroxy-methylene)-3,5-diox ocyclohexanecarboxylic acid ethyl ester] is a foliar-applied growth regulator for turfgrass that can reduce mowing frequency, clipping production, and enhance turfgrass color. C-14-Trinexapac-ethyl was used to evaluate absorption and subsequent C-14-trinexapac-ethyl translocation in hydroponically grown 'Blacksburg' Kentucky bluegrass (Poa pratensis L.). The magnitude and rate of' C-14 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 adjuvant, Sylgard 309, significantly enhanced C-14-trinexapac-ethyl absorption by the leaf blade 1 h after application but did not enhance absorption by the plant base. Of the C-14-trinexapac-ethyl absorbed by the plant base, over 50% was translocated to the plant foliage after 24 h. Of the C-14-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 C-14-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 C-14-trinexapac-ethyl helped explain the positive impact of Sylgard 309 on efficacy and rainfastness of trinexapac-ethyl.