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Xunzhong Zhang and R.E. Schmidt

Superoxide dismutase (SOD) activity is closely associated with stress tolerance of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.) Farw (syn. A. palustris Huds.)]. This study was conducted to investigate the influence of two plant growth regulators (PGRs) on the endogenous antioxidant SOD level and photochemical activity in `Penncross' creeping bentgrass grown under two fertilizer regimes. Mature `Penncross' was treated monthly with TE at 0.44 g a.i./100 m2 and PPC at 3.37 g a.i./100 m2 from May through November at the Virginia Tech Turfgrass Research Center, Blacksburg, Va. Foliar application of TE and PPC increased SOD activity, photochemical activity, and Fm730/Fm690 ratio of creeping bentgrass under the two fertilization regimes as well as when the grass was exposed to a low soil moisture environment. TE reduced clipping weight consistently regardless of the fertilization regime. In contrast, PPC increased clipping weight slightly. Both TE and PPC significantly reduced Dollar spot disease (Sclerotinia homoeocarpa Bennett) under both high and low fertilization regimes. No significant fertilization × PGR interactions for SOD, photochemical activity of PS II, and Fm730/Fm690 were observed in well-watered or drought stressed bentgrass. Improvement in stress tolerance of creeping bentgrass by the PGRs appears to be associated partially with an increase of endogenous SOD activity. Chemical names used: trinexapac-ethyl (TE); propiconazole (PPC).

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J.M. Goatley Jr. and R.E. Schmidt

This study was conducted to determine if foliar-applied biostimulators could enhance harvestability and transplanting of Kentucky bluegrass (Poa pratensis L.) sod. The systemic triazole fungicides propiconazole at 42 mg·m-2 and triadimefon at 150 mg·m-2 enhanced post-transplant rooting and sod strength of bluegrass. Propiconazole had the best sod enhancement effect, increasing sod tensile strength 23% and increasing transplant root lift strength 64% across three experiments. The synthetic cytokinin benzyladenine (BA) at 6 mg·m-2 and seaweed extract (SWE, a freeze-dried extract of the seaweed Ascophyllum nodosum) at 0.3 ml product/m 2 had little effect. The response to triadimefon was intermediate. Foliar applications of chelated Fe phosphate citrate at 112 mg·m-2 did not enhance sod strength or rooting of Kentucky bluegrass when applied either alone or in combination with the biostimulator materials. Chemical names used: l-(2-(2,4 -dichlorophenyl)-4-propyl-l,3-dioxo1an-2-ylmethyl)-lH-l,2,4-triazole(propiconazole);1-(4-chlorophenoxy)-3,3-dimethyl-lH-(l,2,4-triazo1-l-yl)-butanone (triadimefon);6-benzylaminopurine (BA, benzyladenine).

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J.M. Goatley Jr. and R.E. Schmidt

Research was conducted to evaluate crabgrass [Digitaria ischaemum (Schreb.) Muhl.] control, incidental dollar spot (incited by Lanzia and Moellerodiscus spp.) suppression, and turfgrass quality following sequential, low-level postemergence applications of DSMA to creeping bentgrass (Agrostis stolonifera var. palustris Farwell). DSMA was applied at 22 mg·m-2 at 7-day intervals for 15 consecutive weeks (DSMA-W) from May through Aug. 1986 and 1987 and for 10 consecutive weeks from June through Aug. 1988. DSMA also was applied in three split applications of 110 mg·m-2 every 10 days (DSMA-S) in June and July of each year. DCPA was applied in a single, preemergence application in May as a comparative standard for crabgrass control. Percent crabgrass in either DSMA-treated plot was 20% by 11 Sept., an infestation that was unacceptable for high-quality turf. Percent crabgrass infestation was 6% at all rating dates in 1987 or 1988 for DSMA-W and 11% at all dates in 1987 or 1988 for DSMA-S. DCPA significantly reduced percent crabgrass as compared to the nontreated control at all rating dates, but the percent crabgrass ratings tended to be higher than those for either DSMA treatment by the final rating dates of each year. The DSMA treatments significantly reduced dollar spot incidence in each year. Turfgrass discoloration was observed following the DSMA-S treatment in July 1987 as compared to the control, but the turf quality recovered by August. Turfgrass quality was higher for DSMA treatments than for either DCPA or the nontreated control due to season-long crabgrass control and disease suppression. Chemical names used: disodium methanearsonate (DSMA), dimethyl tetrachloroterephthalate (DCPA).

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J.M. Goatley Jr. and R.E. Schmidt

This study was conducted to determine the potential anti-senescence activity of certain chemicals by monitoring changes in gross. CO2 exchange with senescence of excised leaves of Kentucky bluegrass (Poa pratensis L.). One day following foliar applications of benzyladenine (BA), triadimefon, and propiconazole, with and without chelated Fe (8% Fe phosphate citrate), Kentucky bluegrass leaves were excised, floated on distilled water in petri dishes, and placed in a darkened growth chamber. Gross CO2 exchange rates (CER) were recorded 1, 4, 7, and 10 days after excision (DAE). Foliar applications of Fe, BA, triadimefon, or propiconazole applied alone induced an anti-senescence response. Combinations of Fe with the chemicals delayed excision-induced leaf senescence, but no significant increase in anti-senescence activity was obtained from the Fe and chemical combinations as compared to the materials applied alone. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); 1-(4-Chlorophenoxy)-3,3-dimethyl-1(1H-1,2,4-triazol-1yl)-2-butanone (triadimefon);1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole (propiconazole).

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Xunzhong Zhang, E.H. Ervin and R.E. Schmidt

Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, `Moonlight' (dark green) and `Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality by 58% (`Moonlight') and 77% (`Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in `Moonlight' relative to `Limerick' under UV-B stress and during recovery. `Moonlight' contained greater levels of chlorophyll (1.5 to1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than `Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.

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Xunzhong Zhang, R.E. Schmidt, E.H. Ervin and S. Doak

Creeping bentgrass (Agrostis palustris Huds.) is an extensively used cool-season grass for fine turf areas such as golf course putting greens, but suffers from poor summer stress tolerance. These studies were conducted to investigate the influences of natural plant growth regulators (NPGR) and Fe on creeping bentgrass photochemical activity (PA), antioxidant superoxide dismutase (SOD) activity, root growth and leaf color under two fertilization regimes. The bentgrass was maintained in well-watered field conditions or water-stressed glasshouse conditions. A mature bentgrass was treated monthly during the field season with seaweed (Ascophyllum nodosum Jol.) extract (SWE) at 50 mg·m-2 or humic acid (HA) at 150 mg·m-2 or in combination with or without FeSO4 at 520 mg·m-2 and grown under a low or a high fertilization regime. Foliar application of SWE + Fe increased PA (14% to 15%), while applications of SWE + HA or SWE + HA + Fe increased SOD activity (49% to 114%) of creeping bentgrass in Summer 1997 and Summer 1998. There was no significant fertilization × NPGR interaction for PA and SOD activity. Bentgrass PA was increased by 13% to 46% when treated with NPGR with or without Fe compared to the control measured in May. The addition of Fe with each NPGR application improved fall and winter leaf color. All NPGR and Fe treatments increased root mass (17% to 29%) in Aug. 1997 and 1998, except HA alone in 1998. Under sustained low soil moisture (-0.5 MPa) conditions, application of NPGR with or without Fe increased PA and SOD activity. The data indicate that SWE and HA enhance the physiological function of `Southshore' creeping bentgrass, resulting in improved root growth regardless of low or high fertilization regime. However, addition of Fe to these NPGR served primarily to improve late season leaf color. The results suggest that, in addition to maintaining adequate plant-available nutrients, applications of natural PGRs, such as SWE and HA, prior to and during summer abiotic stresses would be beneficial.

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Xunzhong Zhang, E.H. Ervin and R.E. Schmidt

Decline of sod quality during the transportation, storage, and transplant stages of sale is a primary economic concern of sod producers. However, the mechanisms of extending sod quality during storage, transportation, and transplantation remain unclear. This study was conducted to investigate the influences of selected plant metabolic enhancers (PMEs) seaweed (Ascophyllum nodosum Jol.) extract (SWE), humic acid [93% a.i. (HA)], and propiconazole (PPC), on sod tolerance to stress during storage and posttransplant root growth of tall fescue (Festuca arundinacea Schreb.) sod. The SWE + HA, and PPC were applied alone, or in a combination, to tall fescue 2 weeks before harvest. Photochemical efficiency (PE) of photosystem II was measured immediately before harvest. The harvested sod was subjected to high temperature stress (40 °C) for 72 or 96 hours. The heated sod was replanted in the field and posttransplant injury and root strength were determined. On average over 1999 and 2000, application of SWE (50 mg·m-2) + HA (150 mg·m-2), PPC (0.30 mL·m-2), and a combination of SWE + HA with PPC (0.15 mL·m-2), enhanced PE of preharvest sod by 8.5%, 9.1%, and 11.2%, respectively, and increased posttransplant rooting by 20.6%, 34.6%, and 20.2%, respectively. All PME treatments reduced visual injury except SWE + HA and SWE + HA + PPC in 1999. Extension of heat duration from 72 to 96 hours caused significantly more injury to the sod and reduced posttransplant rooting by 22.9% averaged over 2 years. The data suggest that foliar application of SWE + HA, PPC alone, or in a combination with SWE + HA, may reduce shipment heat injury and improve posttransplant rooting and quality of tall fescue sod. Chemical name used: 1-(2-(2,4-dichloropheny)-4-propyl-1,3-dioxolan-2yl)methyl-1-H-1,2,4-triazole [propiconazole (PPC)].

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Xunzhong Zhang, E.H. Ervin and R.E. Schmidt

A variety of organic materials such as humic substances, seaweed extracts (SWE), organic matter, and amino acids are being used as fertilizer supplements in commercial turfgrass management. Among them, SWE and humic acid (HA) are widely used in various biostimulant product formulations. These compounds have been reported to contain phytohormones and osmoprotectants such as cytokinins, auxins, polyamines, and betaines. Manufacturer claims are that these products may supplement standard fertility programs by reducing mineral nutrient requirements while improving stress tolerance. There is a lack of season-long, field-based evidence to support these claims. This study was conducted to investigate the influence of monthly field applications of SWE, HA, and high and low seasonal fertilization regimes on the physiological health of fairway-height creeping bentgrass (Agrostis stolonifera L.). Plots were treated monthly with SWE at 16 mg·m-2 and HA (70% a.i.) at 38 mg·m-2 alone, or in combination, and were grown under low (20 kg·ha-1/month) or high nitrogen (50 kg·ha-1/month) fertilization regimes during 1996 and 1997. Endogenous antioxidant superoxide dismutase (SOD) activity, photochemical activity (PA), and turf quality were measured in July of each year. Superoxide dismutase activity was increased by 46% to 181%, accompanied by a PA increase of 9% to 18%, and improved visual quality of bentgrass in both years. There was no significant fertilization × supplement interaction. Although not part of our original objectives, it was noted that significantly less dollar spot (Sclerotinia homoeocarpa F.T. Bennett) disease incidence occurred in supplement-treated bentgrass. Our results indicate that increased SOD activity in July due to SWE and/or HA applications improved overall physiological health, irrespective of fertilization regime. This suggests that these compounds may be beneficial supplements for reducing standard fertilizer and fungicide inputs, while maintaining adequate creeping bentgrass health.

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M.S. Flanagan, R.E. Schmidt and R.B. Reneau Jr.

The “heavy fraction” portion of a municipal solid waste separation process was evaluated in field experiments as a soil amendment for producing turfgrass sod. Soil organic matter and concentrations of extractable NO3-N, P, K, Ca, and Zn in the soil increased with addition of heavy fraction. Soil incorporation of heavy fraction resulted in greater air, water, and total porosity and lower bulk density of a loamy sandy soil. .Sod strength measurements taken 8.5 and 9.5 months after seeding were higher for Kentucky bluegrass (Poaprutensis L.) grown in heavy-fraction-amended topsoil than for turf grown in topsoil only. The use of this by-product may reduce the time required to produce a marketable sod. Soil incorporation of heavy fraction did not influence post-transplant rooting of Kentucky bluegrass sod but enhanced rooting of bermudagrass [Cynodon dactylon (L.) Pers.] sod at the highest rate evaluated. Results of these studies suggest that the use of heavy fraction for sod production may provide cultural benefits in addition to reducing the volume of solid waste deposited in landfills.