maximum growth inhibition at 2 to 5 wk after PGR applications, along with improvements in turfgrass qual-Research on the gibberellic acid (GA)-inhibiting plant-growth regity. Existing concerns in the golf course industry with ulator (PGR) trinexapac-ethyl (TE) regarding seasonal effects of single vs. multiple applications of this product on turfgrass quality and PGR applications in bermudagrass include turfgrass distissue production has not been reported. Research was conducted at coloration 1 to 2 wk after application and PIGE. Discol-North Carolina State University on 'Tifway' bermudagrass [Cynodon oration has been observed with applications of TE but dactylon (L.) Pers. ϫ Cynodon transvaalensis (Burtt-Davy)] to commay be counteracted by tank mixing TE with an Fe pare effects of different seasonal application patterns of TE. Applicasource (Johnson, 1997; Wiecko, 1997). The literature tions of TE were made to fully established Tifway bermudagrass at has not reported on either PIGE or how it may be either 0.107 or 0.071 kg a.i. ha Ϫ1 . Seasonal application patterns inaffected by the seasonal impact of multiple PGR applicluded an initial application, followed by zero, one, or two sequential cations. applications at 4-wk intervals. Plots were rated weekly for turfgrass Known warm-season turfgrass growth responses to quality and clippings were collected weekly for evaluation of tissue decreasing temperatures and reduced light levels in the production. Results demonstrated that one application of TE provided temporary growth inhibition of Tifway bermudagrass. This effect, as fall include cessation of new growth and net loss of expected, disappeared 4 wk after initial treatment (WAIT). Post-chlorophyll from leaf tissues. Research has been coninhibition growth enhancement (PIGE) was observed from 6 to 10 ducted to investigate how these effects may be delayed WAIT in areas treated with a single application of TE at 0.071 kg or counteracted, presumably to artificially extend the a.i. ha Ϫ1 . However, total seasonal tissue production following a single perceived growth period of these species. Exogenous application of TE was equal to untreated areas, suggesting limited additions of growth-regulating substances such as either overall effects of PIGE. Conversely, one or two sequential applicathe fungicide carboxin or the hormone GA have aided tions of TE provided prolonged growth inhibition; total seasonal tissue in the delay of bermudagrass dormancy symptoms (Diproduction was reduced by up to 40%. Overall quality of Tifway Paola et al., 1981; Dudeck and Peacock, 1985; Karnok bermudagrass was enhanced by multiple TE applications and per-

An experimental turfgrass growth regulator, V-10029, was compared with trinexapac-ethyl, a growth regulator used commonly on highly maintained turfgrasses, to evaluate growth suppression patterns and suppression of seedhead formation; the latter was evaluated on turfgrass species and annual bluegrass, a weedy species that appeared and developed seedheads in tall fescue. Plugs of creeping red fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass were taken from the field into a greenhouse. V-10029 at three rates (0.015, 0.029, and 0.059 kg/ha) was compared to an untreated control and trinexapac-ethyl at a label rate (0.382 kg/ha for perennial ryegrass and 0.287 kg/ha for the other four species). Of the eight replications for each treatment, four were not mowed for the purpose of evaluating suppression of seedhead formation, and four were used for weekly clipping collection to evaluate growth suppression. Compared to the untreated control, V-10029 at all three applied rates caused significant seedhead suppression in both tall fescue infested with annual bluegrass (> 90%) and perennial ryegrass (50 to 80%). Trinexapac-ethyl was not as effective, causing seedhead suppression levels of 57% in annual bluegrass found in tall fescue and 43% in perennial ryegrass. V-10029 caused unacceptable levels of discoloration (> 20%) in all turfgrass species, and discoloration increased with increasing rates of application. Patterns of growth suppression for tall fescue, Kentucky bluegrass, and perennial ryegrass, in response to V-10029 at all rates and to trinexapac-ethyl, were similar on a percent of suppression basis. Growth of creeping bentgrass was suppressed by V-10029 only at high rates. In contrast, creeping red fescue was significantly injured by V-10029 at all rates. The greatest growth suppression, in response for all treatments, occurred 2 to 3 wk after application. The effect of trinexapac-ethyl dissipated after 4 wk, while V-10029 was effective until 5 to 7 wk after treatment. Observed effects of V-10029 were consistent with its activity as an ALS-inhibiting herbicide and, therefore, as a Class D turfgrass growth regulator.

Questions exist as to whether growth-inhibiting chemicals mimic the effects of reduced mowing heights on putting green ball roll. An experiment was initiated during Spring 1997 to investigate ball roll and visual quality parameters of putting greens maintained at 3.2, 4.0, or 4.8 mm with plant growth regulator (PGR) treatments applied monthly over the course of 1 year. Additional experiments were conducted during Fall 1995 and 1996 and Spring 1996 to investigate diurnal PGR effects on ball roll. All experiments were conducted on pure stands of `Penncross' creeping bentgrass (Agrostis palustris Huds). Treatments included trinexapac-ethyl and paclobutrazol, both inhibitors of gibberellin biosynthesis. In the one-year experiment, mowing height was inversely related to ball roll. However, compromises in turfgrass visual quality and shoot density in `Penncross' turf mowed at 3.2 mm make this a questionable mowing height in areas with severe summer conditions. Ball roll during summer months was reduced by PGRs, suggesting that PGRs have little potential as alternatives to decreasing mowing height for increased ball roll. Paclobutrazol reduced turfgrass quality and shoot density during summer months, suggesting that it be used with caution. Other PGRs, particularly trinexapac-ethyl at 0.05 kg·ha–1 a.i., increased afternoon ball roll by as much as 5% to 10% in diurnal experiments. Use of PGRs on creeping bentgrass putting greens may therefore produce short-lived increases in ball roll with subtle to negative effects on bentgrass growth over more extended periods of time. Chemical names used: 4-(cyclopropyl-α-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester (trinexapac-ethyl); (+/–)-(R*,R*)-β-[(4-chloro-phenyl)methyl]-α-(1,1dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

atures and poor soil aeration reduces root growth and root viability in creeping bentgrass, and contributes to Summer decline of creeping bentgrass [Agrostis palustris Huds.summer bentgrass decline (Huang et al., 1998a,b). (ϭAgrostis stolonifera var. palustris (Huds.) Farw.] root growth isStrategies to reduce creeping bentgrass summer root an annual concern in many regions of the USA. A 2-yr field study growth decline have included use of soil amendments North Carolina State Univ.,

Trinexapac-ethyl is a foliar-applied growth regulator for turfgrass that can reduce mowing frequency, clipping production, and enhance turfgrass color. I"C_Trinexapac-ethyl was used to evaluate absorption and subsequent 14C-trinexapac-ethyl translocation in hydroponically grown 'Blacksburg' Kentucky bluegrass (Poa pratensis L.). The magnitude and rate of 14Ctrinexapac-ethyl absorption by various organs was as follows: plant base> leaf blade> roots. Over the time period of 0 to 24 hours, maximum absorption by the plant base was obtained in 8 hours and by the leaf blade in 24 hours. Absorption by the roots was negligible. Addition of an activator organosilicone adjuvant, Sylgard 309~, significantly enhanced 14C-trinexapac-ethyl absorption by the leafblade one hour after application but did not enhance absorption by the plant base. Of the 14C_ trinexapac-ethyl absorbed by the plant base, over 50% was translocated to the plant foliage after 24 hours. Of the 14C-trinexapac-ethyl absorbed by the leaf blade, one-third was translocated after 24 hours; the direction of movement was predominantly basipetal. Less than 5% of absorbed 14C-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 leafblade absorption, basipetal translocation from the leaf blade, and acropetal translocation from the plant base of 14C-trinexapac-ethyl helped explain the positive impact of Sylgard 309~on efficacy and rainfastness of trinexapac-ethyl.