Influence of sequential trinexapac-ethyl applications on cytokinin content in creeping bentgrass, Kentucky bluegrass, and hybrid bermudagrass

Trinexapac-ethyl (TE) is a popular plant growth regulator in the turfgrass industry not only for its effectiveness in reducing mowing requirements but for its positive effects on turf density and appearance. We hypothesized that reported side effects of TE such as increases in color, photochemical efficiency (PE) of photosystem 11, tillering, and chlorophyll, may be related to changes in leaf cytokinin content. Our objective was to determine if TE influences leaf trans-zeatin riboside (t-ZR) content of three common turfgrass species. Sods of Kentucky bluegrass (Poa pratensis L.), creeping bentgrass (Agrostis stolonifera L.), and hybrid bermudagrass (Cynodon dactylon x C. transvaalensis) were transplanted and grown in flats under a greenhouse mist system. Label-rate TE treatments were applied every 2 wk for 2 mo. Canopy PE, leaf color, canopy height, and leaf t-ZR contents were measured every 2 wk in 2003, with leaf total nonstructural carbohydrates (TNC) measurements added in 2004. A significant increase in t-ZR content was measured following sequential TE treatment in all three species in both years. Leaf TNC was consistently increased following the second TE application in creeping bentgrass and hybrid bermudagrass. While our data are nonspecific as to how TE increases leaf t-ZR, it appears that a shift in assimilate partitioning to basal organs could be a contributing factor. Whatever the mechanism, increased leaf t-ZR is likely to confer aesthetic, as well as functional, advantages to treated turfgrasses.