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Maria P. Fuentealba, Jing Zhang, Kevin E. Kenworthy, John E. Erickson, Jason Kruse, and Laurie E. Trenholm

Irrigation for commercial and residential turf is becoming limiting, and water scarcity is one of the long-term challenges facing the turfgrass industry. Potential root development and profile characteristics of turfgrass provide important information regarding their drought resistance mechanisms and developing drought-resistant cultivars. The objective of this study was to determine the potential root development and root profile characteristics of two bermudagrass species and two zoysiagrass species using experimental lines and commercial cultivars. The species evaluated in the study were: African bermudagrass (Cynodon transvaalensis Burtt-Davy), common bermudagrass (CB) [Cynodon dactylon (L.) Pers. var. dactylon], Zoysia japonica (ZJ) (Steud), and Zoysia matrella (ZM) L. Plants were grown outdoors in clear acrylic tubes encased in poly vinyl chloride (PVC) sleeves. The experimental design was randomized complete block design with four replications. Rates of root depth development (RRDD) during the first 30 days were obtained. Root length density (RLD) in four different horizons (0–30, 30–60, 60–90, and 90–120 cm) was determined 60 days after planting. Specific root length (SRL, m·g−1) was also calculated dividing total root length by total root dry weight (RDW). The root depth in four turfgrass species increased linearly during the first 30 days after planting. Common bermudagrass (CB) had high RRDD and uniform RLD in different horizons, while ZM accumulated the majority of its roots in the upper 30 cm. Z. matrella had higher RLD than CB in the upper 30 cm. African bermudagrass had higher SRL than CB. There was limited variation within the two African bermudagrass genotypes studied except at the lowest horizon (90–120 cm). Two genotypes in CB and ZJ, respectively, including ‘UF182’ (ZJ), which consistently ranked in the top statistical group for RRDD, and RLD for every horizon, and ‘UFCD347’ (CB) demonstrated greater RLDs in the lower horizons in comparison with the commercial cultivars.

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Dana Sullivan, Jing Zhang, Alexander R. Kowalewski, Jason B. Peake, William F. Anderson, F. Clint Waltz Jr., and Brian M. Schwartz

Quantitative spectral reflectance data have the potential to improve the evaluation of turfgrasses in variety trials when management practices are factors in the testing of turf aesthetics and functionality. However, the practical application of this methodology has not been well developed. The objectives of this research were 1) to establish a relationship between spectral reflectance and turfgrass quality (TQ) and percent green cover (PGC) using selected reference plots; 2) to compare aesthetic performance (TQ, PGC, and vegetation indices) and functional performance (surface firmness); and 3) to evaluate lignin content as an alternate means to predict surface firmness in turfgrass variety trials of hybrid bermudagrass [Cynodon dactylon × C. transvaalensis]. A field study was conducted on mature stands of three varieties (‘TifTuf’, ‘TifSport’, and ‘Tifway’) and two experimental lines (04-47 and 04-76) at two mowing heights (0.5 and 1.5 inch) and trinexapac-ethyl application (0.15 kg·ha−1 and nontreated control) treatments. Aesthetic performance was estimated by vegetation indices, spectral reflectance, visual TQ, and PGC. The functional performance of each variety/line was measured through surface firmness and fiber analysis. Regression analyses were similar when using only reference plots or all the plots to determine the relationship between individual aesthetic characteristics. Experimental line 04-47 had lower density in Apr. 2010, whereas varieties ‘TifTuf’, ‘TifSport’, and ‘Tifway’ were in the top statistical group for aesthetic performance when differences were found. ‘TifSport’ and ‘Tifway’ produced the firmest surfaces, followed by ‘TifTuf’, and finally 04-76 and 04-47, which provided the least firm surface. Results of leaf fiber analysis were not correlated with turf surface firmness. This study indicates that incorporating quantitative measures of spectral reflectance could reduce time and improve precision of data collection as long as reference plots with adequate range of green cover are present in the trials.

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Yiwei Jiang and Robert N. Carrow

Canopy reflectance has the potential to determine turfgrass shoot status under drought stress conditions. The objective of this study was to describe the relationship of turf quality and leaf firing versus narrow-band canopy spectral reflectance within 400 to 1100 nm for different turfgrass species and cultivars under drought stress. Sods of four bermudagrasses (Cynodon dactylon L. × C. transvaalensis), three seashore paspalums (Paspalum vaginatum Swartz), zoysiagrass (Zoysia japonica), and st. augustinegrass (Stenotaphrum secundatum), and three seeded tall fescues (Festuca arundinacea) were used. Turf quality decreased 12% to 27% and leaf firing increased 12% to 55% in 12 grasses in response to drought stress imposed over three dry-down cycles. The peak correlations occurred at 673 to 693 nm and 667 to 687 nm for turf quality and leaf firing in bermudagrasses, respectively. All three tall fescues had the strongest correlation at 671 nm for both turf quality and leaf firing. The highest correlations in the near-infrared at 750, 775, or 870 nm were found in three seashore paspalums, while at 687 to 693 nm in Zoysiagrass and st. augustinegrass. Although all grasses exhibited some correlations between canopy reflectance and turf quality or leaf firing, significant correlation coefficients (r) were only observed in five grasses. Multiple linear regression models based on selected wavelengths for turf quality and leaf firing were observed for 7 (turf quality) and 9 (leaf firing) grasses. Wavelengths in the photosynthetic region at 658 to 700 nm or/and near-infrared from 700 to 800 nm predominated in models of most grasses. Turf quality and leaf firing could be well predicted in tall fescue by using models, evidenced by a coefficient of determination (R 2) above 0.50. The results indicated that correlations of canopy reflectance versus turf quality and leaf firing varied with turfgrass species and cultivars, and the photosynthetic regions specifically from 664 to 687 nm were relatively important in determining turf quality and leaf firing in selected bermudagrass, tall fescue, zoysiagrass and st. augustinegrass under drought stress.

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Glenn R. Wehtje, Joey N. Shaw, Robert H. Walker, and Walker Williams

Various inorganic soil amendments have been promoted as a means of improving the chemical and physical properties of certain soils. To test this hypothesis, a marginally productive soil was supplemented with 20%, 40%, 60%, and 80% (v/v) of either selected inorganic amendments or sand. Amendments consisted of commercially available diatomaceous earth, calcined clay, zeolite, and crystalline SiO2. The soil material was extracted from the argillic horizon of a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Ability of these soil-amendment mixtures to promote `Tifway' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] growth was evaluated under greenhouse conditions, and contrasted to that obtained in nonamended soil. Selected chemical and physical properties that are pertinent to plant growth were also evaluated. The experiment, which was conducted 3×, began with a §60-day period in which both water and nutrients were optimum. This was followed by a 30-day drought. During optimum water and nutrients, no soil-amendment treatment(s) consistently resulted in superior bermudagrass growth compared to soil alone. However, <2% of the bermudagrass tissue that was produced during the drought became green and succulent with the resumption of irrigation in nonamended soil. This percentage was exceeded by all treatments that contained either ≥60% diatomaceous earth (Axis), or ≥40% calcined clay (Profile); and by 100% zeolite (Clinolite) and 100% silica (Green's Choice). Drought-sustaining ability of soil-amendment mixtures was significantly (P < 0.05) correlated with water-holding ability, soil strength, bulk density, and oxygen diffusion rate, but not correlated with either pH or cation exchange capacity (CEC). While certain inorganic amendments did improve the drought-sustaining ability of soil, the amount required was generally ≥40%.

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Jordan M. Craft, Christian M. Baldwin, Wayne H. Philley, James D. McCurdy, Barry R. Stewart, Maria Tomaso-Peterson, and Eugene K. Blythe

Traditional hollow-tine (HT) aerification programs can cause substantial damage to the putting green surface resulting in prolonged recovery. Despite the growing interest in new and alternative aerification technology, there is a lack of information in the literature comparing new or alternative technology with traditional methods on ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens. Therefore, the objective of this research was to determine the best combination of dry-injection (DI) cultivation technology with modified traditional HT aerification programs to achieve minimal surface disruption without a compromise in soil physical properties. Research was conducted at the Mississippi State University golf course practice putting green from 1 June to 31 Aug. 2014 and 2015. Treatments included two HT sizes (0.6 and 1.3 cm diameter), various DI cultivation frequencies applied with a DryJect 4800, and a noncultivated control. The HT 1.3 cm diameter tine size had 76% greater water infiltration (7.6 cm depth) compared with the DI + HT 0.6 cm diameter tine size treatment. However, DI + HT 0.6 cm diameter tine size had greater water infiltration at the 10.1 cm depth than the noncultivated control. Results suggest a need for an annual HT aerification event due to reduced water infiltration and increased volumetric water content (VWC) in the noncultivated control treatment. It can be concluded that DI would be best used in combination with HT 1.3 or 0.6 cm diameter tine sizes to improve soil physical properties; however, the DI + HT 0.6 cm diameter tine size treatment resulted in minimum surface disruption while still improving soil physical properties compared with the noncultivated control.

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G.A. Picchioni and Héctor M. Quiroga-Garza

Two greenhouse studies were conducted to trace the fate of fertilizer N in hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy `Tifgreen'], and to estimate total plant N recovery and losses. The first experiment was performed during winter, with artificial light supplementing natural light to provide a photoperiod of 13.6 to 13.8 hours. The second experiment was conducted during summer and fall under only natural light conditions, with a progressively decreasing photoperiod of 13.7 to 11.1 hours. Urea (UR), ammonium sulfate (AS), and ammonium nitrate (AN) were labeled at 2 atom% 15N, and applied at N rates of 100 or 200 kg·ha-1 for 84 days (divided into six equal fractions and applied every 14 days). Fertilizer N source did not affect total dry matter (DM) accumulation by the plant components, but the high N rate increased clipping DM production under the longer photoperiod. Under the decreasing photoperiod, overall DM production was reduced, and clipping DM production was unaffected by increased N rate. Average N concentration of clippings varied between N sources, ranging from a high of 38.6 g·kg-1 DM with AS to a low of 34.7 g·kg-1 for UR. In Expt. 1, the greatest total plant N recovery [clippings, verdure (shoot material remaining after mowing), and thatch plus roots] occurred with AS (78.5%) and the lowest with UR (65.9%). In Expt. 2, these values declined to 53.0% and 38.0%, respectively. Urea fertilization resulted in the greatest N losses as a fraction of the N applied (33.6% to 61.5%) and AS fertilization the lowest (20.7% to 46.3%). In view of the greater N losses, UR may be a less suitable soluble N source for bermudagrass fertilization within the conditions of this study. In addition, late-season N fertilization may result in a significant waste of fertilizer N as bermudagrass progresses into autumnal dormancy when temperature, photoperiod, and irradiance decline and cause reduction in growth and N uptake.

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Héctor Mario Quiroga-Garza and Geno A. Picchioni

Total plant biomass, shoot growth rate, and the periodicity in shoot growth and color of hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy `Tifgreen'] in response to slow-release fertilizer N sources, rates, and application frequencies were studied in two, 120-day greenhouse studies. Plugs were planted in plastic cylinders filled with a growing medium of 93 sand: 7 peat moss (w/w). The first experiment was completed under progressively increasing photoperiod (13.1 to 14.9 hours) typical of the long-day requirements for bermudagrass growth. The second experiment occurred under progressively decreasing photoperiod (13.7 to 10.7 hours) representative of autumnal growing conditions and declining growth and N demand. Urea (URE), sulfur-coated urea (SCU), and hydroform (HYD, methylene urea polymers) were broadcast at N rates of 100 or 200 kg·ha-1 and at frequencies of 20 or 40 days. Bermudagrass was clipped at 3-day intervals and the average daily clipping growth rate (increase in shoot dry matter; DM) reached a maximum of 11.5 g·m-2 per day. Use of the least soluble source, HYD, produced the lowest total clipping DM, and at low HYD rate and frequency, leaf color intensity was frequently below the accepted standard of 7, in the scale from 1 “tan” to 9 “dark green”. A greater responsiveness of bermudagrass to N rate and application frequency (increased clipping growth rate and color intensification upon N application) occurred under increasing photoperiodic conditions as compared to decreasing photoperiodic conditions. Both clipping growth and color changed cyclically through time and mainly under long-day photoperiod (>12 hours), with greater oscillation at longer fertilization interval (40 days). With either SCU or URE, at low N rate and frequency (total N application of 0.25 g·m-2 per day), clipping growth rates were above 4 g·m-2 per day, and turf color was at or above the minimum quality standard through most of the growing period. Higher total SCU and URE application rates, previously shown to increase N leaching losses in these experimental conditions, produced significantly more clipping growth and did not appear to intensify color sufficient to warrant the increased risk of N loss.

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D.W. Williams and P.B. Burrus

Perennial ryegrass (PR) (Lolium perenne L.) is often used as a low-mowed turf in the transition climatic zone. However, control of the fungal disease gray leaf spot (Pyricularia grisea (Cooke) Sacc.) has drastically increased the cost of PR management. Seeded bermudagrasses (SB) [Cynodon dactylon (L.) Pers.] are viable options for turfgrass management operations with limited pesticide budgets. Field trials in 2000 and 2001 tested the effects of two herbicides and several plant growth regulators (PGR) during renovation of mature PR to either of two cultivars of SB. The herbicides glyphosate and pronamide, and the PGR's trinexapac-ethyl, ethephon, paclobutrazol, and flurprimidol were applied at label rates to mature stands of PR. `Mirage' and `Yukon' SB were seeded separately either 1 or 7 days after applications (DAA) of chemicals. SB establishment, first-winter survival, and turfgrass quality (TQ) were rated and compared to an untreated control. Results indicated that only applications of glyphosate resulted in acceptable renovation of PR to SB, but also resulted in significantly lower (P< 0.05) TQ during the transition. Applications of pronamide resulted in significantly less (P < 0.05) SB transition than did applications of glyphosate, but pronamide plots maintained higher TQ. None of the PRG treatements had a significant effect (P < 0.05) on SB transition. There were no consistent significant effects (P < 0.05) due to DAA among any of the chemicals evaluated. First-winter survival was significantly higher (P < 0.05) with `Yukon' than with `Mirage' in both years. We conclude that among the chemicals tested, only applications of glyphosate resulted in acceptable transition of PR to SB, but a significant reduction of TQ should be expected during the transition. Chemical names used: [N-(phosphonomethyl) glycine] (glyphosate); [3.5-dichloro-N-(1,1-dimethyl-2-propynyl)-benzamide] (pronamide); [(2-chloroethyl) phosphonic acid] (ethephon); [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane-cabroxylic acid ethyl ester] (trinexapac-ethyl); [(±)-(R*R*)β-[(4-chlorophenyl)-methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol] (paclobutrazol); [α-(1-methylethyl)-α-[4-(trifluromethoxy)phenyl]-5-pyrmidinemethanol] (flurprimidol).

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Robert L. Green, Grant J. Klein, Francisco Merino, and Victor Gibeault

Bermudagrass [Cynodon dactylon (L.) Pers × C. transvaalensis Burtt-Davy] greens across the southern United States are normally overseeded in the fall to provide a uniform green playing surface and tolerance to wear during winter bermudagrass dormancy. The spring transition from overseed grass back to bermudagrass is a major problem associated with overseeding because there can be a decline in putting green quality and playability. There have been recommendations, but relatively few published reports, on the effect of treatments associated with seedbed preparation and overseeding on bermudagrass spring transition. The objective of this 2-year study was to determine if spring transition of an overseeded `Tifgreen' bermudagrass green was influenced by fall-applied scalping level, chemical, and seed rate treatments. Treatment factors and levels were designed to reflect the range of practices used by golf course superintendents in the region at the time of the study. The green was located in the Palm Springs, Calif. area, which has relatively mild winters and a low desert, southern Calif. climate. The first year of the study was from September 1996 to July 1997 and the second year was from September1997 to July 1998. Scalping level treatments included a moderate and severe verticut and scalp; chemical treatments included a check, trinexapac-ethyl at two rates, and diquat; and seed rate treatments included a high and low rate of a mixture of `Seville' perennial ryegrass (Lolium perenne L.) and `Sabre' rough bluegrass (Poa trivialis L.). The plot was maintained under golf course conditions and a traffic simulator was used to simulate golfer traffic. Visual ratings of percent green bermudagrass coverage were taken every 3 weeks from 20 Feb. 1997 to 29 July 1997 and from 11 Nov. 1997 to 22 July 1998. Visual turfgrass quality ratings were taken during the second year of the study. Results showed that spring transition was not influenced by fall-applied treatments during both years. Also, visual turfgrass quality was not influenced during the second year. Chemical names used [4(cyclopropyl-_hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); 9,10-dihydro-8a-, 10a-diazoniaphenanthrene (diquat).

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Robert L. Green, Grant J. Klein, Francisco Merino, and Victor Gibeault

Bermudagrass [Cynodon dactylon (L.) Pers × C. transvaalensis Burtt-Davy] greens across the southern United States are normally overseeded in the fall to provide a uniform green playing surface and tolerance to wear during winter bermudagrass dormancy. The spring transition from overseed grass back to bermudagrass is a major problem associated with overseeding because there can be a decline in putting green quality and playability. There have been recommendations, but relatively few published reports, on the effect of treatments associated with seedbed preparation and overseeding on bermudagrass spring transition. The objective of this 2-year study was to determine if spring transition of an overseeded `Tifgreen' bermudagrass green was influenced by fall-applied scalping level, chemical, and seed rate treatments. Treatment factors and levels were designed to reflect the range of practices used by golf course superintendents in the region at the time of the study. The green was located in the Palm Springs, Calif., area, which has relatively mild winters and a low desert, southern California climate. The first year of the study was from Sept. 1996 to July 1997 and the second year was from Sept. 1997 to July 1998. Scalping level treatments included a moderate and severe verticut and scalp; chemical treatments included a check, trinexapac-ethyl at two rates, and diquat; and seed rate treatments included a high and low rate of a mixture of `Seville' perennial ryegrass (Lolium perenne L.) and `Sabre' rough bluegrass (Poa trivialis L.). The plot was maintained under golf course conditions and a traffic simulator was used to simulate golfer traffic. Visual ratings of percent green bermudagrass coverage were taken every 3 weeks from 20 Feb. 1997 to 29 July 1997 and from 11 Nov. 1997 to 22 July 1998. Visual turfgrass quality ratings were taken during the second year of the study. Results showed that spring transition was not influenced by fall-applied treatments during both years. Also, visual turfgrass quality was not influenced during the second year. Chemical names used: [4(cyclopropyl-αhydroxy-methylene) -3,5-dioxocyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); 9,10-dihydro-8a-, 10a-diazoniaphenanthrene (diquat).