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E.H. Ervin, Xunzhong Zhang, J.M. Goatley Jr., and S.D. Askew

Creeping bentgrass (Agrostis stolonifera) is used extensively on temperate zone golf course greens, tees, and fairways, but often performs poorly in shade. Previous research has indicated that sequential applications of gibberellic acid (GA) inhibiting plant growth regulators (PGRs) such as trinexapac-ethyl (TE) increase cool-season turfgrass performance in 70-90% shade. This research was conducted to: 1) confirm appropriate TE application rates and frequencies for maintaining `Penncross' creeping bentgrass in dense shade in the mid-Atlantic region of the U.S.; 2) determine the efficacy of other PGRs, biostimulants, and iron (Fe); and 3) assess whether the addition of a biostimulant with TE would have additive, synergistic, or negative effects. The other compounds tested against TE and the control were: propiconazole (PPC), iron sulfate, CPR (a seaweed and iron containing biostimulant), and a generic seaweed extract (SWE) (Ascophyllum nodosum) plus humic acid (HA) combination. These treatments were applied to 88% shaded bentgrass every 14 days from May or June through October in 2001 and 2002, with turf quality, leaf color, root strength, photochemical efficiency, and antioxidant enzyme superoxide dismutase (SOD) activity being determined. While the quality of control plots fell below a commercially acceptable level by the second month of the trial, repeated foliar TE application provided 33% to 44% better quality throughout the experiment. Propiconazole resulted in 13% to 17% better quality through September of each year. Trinexapac-ethyl and PPC resulted in darker leaf color and increased mid-trial root strength by 27% and 29%, respectively. Canopy photochemical efficiency and leaf SOD activity were also increased due to TE in August of both years. Treatment with Fe, CPR, or SWE+HA did not have an effect on quality, root strength, SOD, or photochemical efficiency, but periodic increases in color were observed. The addition of CPR to TE in 2002 provided results that were not different from those of TE-alone. This and previous studies indicate that restricting leaf elongation with anti-GA PGRs is of primary importance for improving shade tolerance, while treatments that increase leaf color or chlorophyll levels without restricting leaf elongation are relatively ineffective.

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J.M. Goatley Jr., D.B. Smith, P.D. Gerard, and G.E. Coats

Research was conducted to evaluate the performance of a hydraulically driven turfgrass sod strength machine equipped with a force transducer to measure various strength parameters. The most commonly reported strength parameter, peak force (PF), continued to provide the quickest and easiest measurements of sod strength. Calculations of work involving the continuous measurement of sod strength over the duration of the stretch did not consistently improve the information provided by the PF measurement. Changes in sod bed pull speeds altered the calculations of work, whereas pull speed changes generally had little effect on force measurements, an important consideration for sod strength measurement devices that have limited control of sod bed pull speed. The unit was marginally successful in distinguishing sod strength differences between St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze.] treated with various levels of pyridine herbicides. The device also provided strength parameters that distinguished the relative strengths of four warm-season turfgrass sods.

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H.W. Philley, C.E. Watson Jr., J.V. Krans, J.M. Goatley Jr., and F.B. Matta

The objective of this study was to relate the lethal freezing temperatures of St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] genotypes, as measured by differential thermal analysis (DTA), to winter survival observed in the field. DTA-predicted lethal temperatures of 14 St. Augustinegrass genotypes ranged from –7.7 to –4.7C. Regression of field winter survival vs. DTA-predicted lethal temperatures resulted in an r 2 = 0.57 for one field trial that evaluated cultivars with a relatively narrow range of expected freezing tolerance. In a second study evaluating cultivars with a greater range of freezing tolerance, r 2 was 0.92 when winter survival was regressed on DTA-predicted lethal temperatures. DTA was successful in measuring freezing avoidance of St. Augustinegrass cultivars.