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  • Author or Editor: Lambert McCarty x
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Use of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] on golf greens has expanded into the hotter, more humid regions of the United States where its quality is often low during summer months. The summer decline in bentgrass quality may be partially attributed to respiration rates exceeding photosynthesis during periods of supraoptimal temperatures and adverse soil conditions, such as excessive CO2 and inadequate O2 levels. The objectives of this study were to examine the effects of high temperature, high soil CO2, and irrigation scheduling on creeping bentgrass growth. A growth chamber study was conducted using `A-1' creeping bentgrass. Treatments included all combinations of three day/night temperature regimes (26.5/21 °C, 29.5/24 °C, and 32/26.5 °C), three irrigation schedules (field capacity daily, field capacity every two d, and half field capacity daily), and four soil CO2 injection levels (10%, 5%, 0.03%, and a noinjection control). Creeping bentgrass shoot and root dry weights and net photosynthetic rates were greater for day/night temperatures <32/26.5 °C. High temperatures (32/26.5 °C) and 10% CO2 reduced bentgrass net photosynthesis by 37.5 μmol CO2/m2/s. Shoot and root total nonstructural carbohydrates also were lowest for highest temperature regime. Respiration exceeded gross photosynthesis at 32/26.5 °C when 5% and 10% CO2 injection levels were used, indicating a carbon deficit occurred for these conditions. Irrigation volume and frequency did not affect bentgrass growth. High temperatures combined with high soil CO2 levels produced poorest turf quality.

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Dwarf-type bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey] tolerate long-term golf green mowing heights but require heavy nitrogen (N) fertilizations. Inhibiting leaf growth with trinexapac-ethyl (TE) could reduce shoot growth competition for root reserves and improve nutrient use efficiency. Two greenhouse experiments evaluated four N levels, 6 (N6), 12 (N12), 18 (N18), and 24 (N24) kg N/ha/week, with TE at 0 and 0.05 kg·ha–1 a.i. every 3 weeks to assess rooting, nutrient allocation, clipping yield, and chlorophyll concentration of `TifEagle' bermudagrass grown in PVC containers built to U.S. Golf Association specification. Trinexapac-ethyl enhanced turf quality on every date after initial application. After 8 weeks, high N rates caused turf quality decline; however, TE treated turf averaged about 25% higher visual quality from nontreated turf, masking quality decline of high N fertility. `TifEagle' bermudagrass treated with TE had clippings reduced 52% to 61% from non-TE treated. After 16 weeks, bermudagrass treated with TE over all N levels had 43% greater root mass and 23% enhanced root length. Compared to non-TE treated turf, leaf N, P, and K concentrations were consistently lower in TE treated turf while Ca and Mg concentrations were increased. Root N concentrations in TE treated turf were 8% to 11% higher for N12, N18, and N24 fertilized turf than respective N rates without TE. Compared to non-TE treated turf, clipping nutrient recoveries were reduced 69% to 79% by TE with 25% to 105% greater nutrients recovered in roots. Bermudagrass treated with TE had higher total chlorophyll concentrations after 8 and 12 weeks. Overall, inhibiting `TifEagle' bermudagrass leaf growth appears to reallocate nutrients to belowground tissues, thus improving nutrient use efficiency and root growth. Chemical name used: trinexapac-ethyl, [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethylester].

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Creeping bentgrass (Agrostis stolonifera var. palustris Huds.) is desirable as a putting green turfgrass in the transition zone as a result of year-round green color, ball roll, and playability. However, management challenges exist for bentgrass greens, including winter temperature fluctuations. Frosts often cause cancellations or delays of tee time resulting in lost revenue. In response to this winter golf course management issue, a research project was initiated at Clemson University from 1 Dec. 2005 and 2006 to 1 Aug. 2006 and 2007 on a ‘L93’ creeping bentgrass putting green to determine the impacts of foot traffic or mower traffic and time of traffic application on bentgrass winter performance. Treatments consisted of no traffic (control), foot traffic, and walk-behind mower traffic (rolling) at 0700 and 0900 hr when canopy temperatures were at or below 0 °C. Foot traffic included ≈75 steps within each plot using size 10 SP-4 Saddle Nike golf shoes (soft-spiked sole) administered by a researcher weighing ≈75 kg. A Toro Greensmaster 800 walk-behind greens mower weighing 92 kg with a 45.7-cm roller was used for rolling traffic. Data collected included canopy and soil temperatures (7.6 cm depth), visual turfgrass quality (TQ), clipping yield (g·m−2), shoot chlorophyll concentration (mg·g−1), root total nonstructural carbohydrates (TNC) (mg·g−1), soil bulk density (g·cm−3), and water infiltration rates (cm·h−1). Time and type of traffic significantly influenced bentgrass winter performance. On all TQ rating dates, 0700 hr rolling traffic decreased TQ by ≈1.1 units compared with foot traffic at 0700 hr. In December, regardless of traffic application time, rolling traffic reduced bentgrass shoot growth ≈17%. However, in February, chlorophyll, soil bulk density, and water infiltration differences were not detected. By the end of March, all treatments had acceptable TQ. Root TNC was unaffected in May, whereas shoot chlorophyll concentrations were unaffected in May and August. This study indicates bentgrass damage resulting from winter traffic is limited to winter and early spring months and full recovery should be expected by summer.

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Weed competition is a main factor limiting sweetpotato [Ipomoea batatas (L.) Lam] production. Yellow nutsedge (Cyperus esculentus L.) is a problematic weed to control due to its ability to quickly infest a field and generate high numbers of tubes and shoots. Compounding this is the lack of a registered herbicide for selective postemergence control of yellow nutsedge. Research was conducted to evaluate the bentazon dose response of two sweetpotato cultivars and one advanced clone and to evaluate the plant hormone melatonin to determine its ability to safen bentazon post emergence. Bioassays using Murashige and Skoog (MS) media supplemented with melatonin (0.232 g a.i./L and 0.023 g a.i./L) and bentazon (0.24 g a.i./L) were conducted to evaluate the effect of bentazon on sweetpotato and to determine the interactive response of the Beauregard cultivar to bentazon and exogenous applications of melatonin. Beauregard swas the most tolerant cultivar and required dosages of bentazon that were two-times higher to cause the same injury compared with other cultivars. MS media containing melatonin and bentazon showed fewer injuries and higher plant mass than plants treated with bentazon alone. These results indicate that sweetpotato injury caused by bentazon may be reduced by melatonin.

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Annual bluegrass (Poa annua L.) can be a troublesome weed to control in established turfgrass stands; it has developed herbicide resistance after repeated use of products with similar modes of action, and several new herbicides have been registered for use on turfgrasses. Four field studies were conducted near Clemson, S.C., from 2003 through 2005 to evaluate postemergence annual bluegrass control in dormant, nonoverseeded bermudagrass [Cynodon dactylon (L.) Pers.] turf using various herbicides applied in either December or February of each year and rated in the spring. Annual bluegrass control can be accomplished in dormant, nonoverseeded bermudagrass turf using a wide range of products applied in either December or February. Flazasulfuron, foramsulfuron, glufosinate, glufosinate + clethodim, glufosinate + glyphosate, glyphosate + clethodim, glyphosate + diquat, pronamide, rimsulfuron, and trifloxysulfuron provided 87% or greater annual bluegrass control regardless of application timing. Imazaquin and simazine controlled annual bluegrass greater than 85% when applied in December but less than 80% when applied in February. Glyphosate provided 93% annual bluegrass control when applied in February but only 72% control with December applications. No detrimental effects on bermudagrass spring greenup were observed for any herbicide treatment or application time. The availability of several effective herbicide options with differing modes of action provides turfgrass managers with the opportunity to use herbicide rotations that may prevent, or at least delay, the development of resistant annual bluegrass populations to these chemical products.

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Seasonal variations in temperature and solar radiation in the warm climatic region of the transition zone increase difficulty of creeping bentgrass [Agrostis stolonifera var. palustris (Huds.)] management throughout the year. The impact of winter shade on bentgrass quality and subsequent residual effects of winter shade in spring and summer months has not been investigated. Therefore, a 2-year field study investigated trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester] as a winter management strategy to alleviate winter shade stress and determined the winter shade tolerance of ‘L-93’ creeping bentgrass under various reduced light environments. Treatments included a full-sunlight control; 58% and 96% morning, afternoon, and full-day shade artificial; and TE (0.02 kg a.i./ha) applied every 2 weeks from December to July. Data collection included daily light measurements (photosynthetic photon flux density), monthly canopy and soil temperatures, visual turfgrass quality (TQ), chlorophyll concentration, clipping yield, total root biomass, and total root nonstructural carbohydrates. Under 96% shade, canopy temperatures were reduced ≈57% from December to February, whereas soil temperatures were reduced 39% in February compared with full sunlight. Afternoon shade (58%) maintained acceptable TQ throughout winter for both years. Applying TE every 2 weeks in the winter negatively impacted bentgrass quality; however, TE enhanced spring and summer quality. Morning or afternoon shade minimally impacted parameters measured. Overall, moderate winter shade may not limit ‘L-93’ creeping bentgrass performance as a putting green in the transition zone. Results suggest winter shade does not contribute to creeping bentgrass summer decline because all shade-treated plots fully recovered from shade damage in spring months.

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Overseeded perennial ryegrass (Lolium perenne L.) aggressively competes with bermudagrass [Cynodon dactylon (L.) Pers.] for resources and may adversely affect spring transition by releasing allelochemicals into the environment. Growth chamber studies examined germination and growth of ‘Arizona Common’ bermudagrass in soil amended with 0%, 2%, 12%, or 23% perennial ryegrass root or shoot debris or in soil treated with irrigation water in which perennial ryegrass roots at 0, 5, 10, or 20 g·L−1 or shoots at 0, 10, or 20 g·L−1 had been soaked. Inhibitory effects on bermudagrass germination and growth were most extensive when soil was amended with ryegrass shoot debris, because germination, root ash weight, root length density, and root mass density were reduced 33%, 55%, 30%, and 52%, respectively. Soil amended with ryegrass root debris only inhibited bermudagrass-specific root length. Application of irrigation water containing either ryegrass root or shoot extracts only inhibited bermudagrass-specific root length. In conclusion, results obtained when soil was amended with shoot debris demonstrated perennial ryegrass can inhibit bermudagrass germination and growth in controlled environments.

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Summer annual grassy weeds such as goosegrass (Eleusine indica L. Gaertn.) continue to be problematic to control selectively with postemergence (POST) herbicides within turfgrass stands. In recent years, reduced performance by certain herbicides (e.g., foramsulfuron), cancellation of goosegrass-specific herbicides (e.g., diclofop-methyl), and cancellation and/or severe use reductions of other herbicides [e.g., monosodium methanearsonate (MSMA)] have limited the options for satisfactory control and maintenance of an acceptable (≤30% visual turfgrass injury) turfgrass quality. Currently available herbicides (e.g., topramezone and metribuzin) with goosegrass activity typically injure warm-season turfgrass species. The objectives of this research were to evaluate both ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. ×Cynodon transvaalensis Burtt-Davy] injury after treatment with POST herbicides, and to determine whether irrigating immediately after application reduces turfgrass injury. Treatments were control (± irrigation); topramezone (Pylex 2.8C; ± irrigation); carfentrazone + 2,4-D + dicamba + 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP) (Speedzone 2.2L; ± irrigation); carfentrazone + 2,4-D + dicamba + MCPP in combination with topramezone (± irrigation); metribuzin (Sencor 75DF; ± irrigation); mesotrione (Tenacity 4L; ± irrigation); simazine 4L (±irrigation); and mesotrione + simazine (± irrigation). Irrigated treatments were applied immediately with a hand hose precalibrated to apply 0.6 cm or 0.25 inch (≈6.3 L). Visual turfgrass injury for combined herbicide treatments for the irrigated plots was 6% 4 days after treatment (DAT), 12% 1 week after treatment (WAT), 17% 2 WAT, and 6% 4 WAT, whereas nonirrigated plots had turfgrass injury of 14% at 4 DAT, 31% 1 WAT, 35% 2 WAT, and 12% 4 WAT. Irrigated pots had normalized differences vegetative indices (NDVI) ratings of 0.769 at 4 DAT, 0.644 at 1 WAT, 0.612 at 2 WAT, and 0.621 at 4 WAT, whereas nonirrigated plots had the lowest (least green) turfgrass NDVI ratings of 0.734 at 4 DAT, 0.599 at 1 WAT, 0.528 at 2 WAT, and 0.596 at 4 WAT. These experiments suggest turfgrass injury could be alleviated by immediately incorporating herbicides through irrigation.

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Goosegrass (Eleusine indica L. Gaertn.) is a problematic C4 weedy grass species, occurring in the warmer regions of the world where it is difficult to selectively control without injuring the turfgrass. Furthermore, control efficacy is affected by plant maturity. End-user options for satisfactory goosegrass control has decreased; thus, the need for developing management techniques to improve the selectivity of POST goosegrass control options in turfgrass systems is ever increasing. One possible means of providing control, yet maintaining turf quality is immediately incorporating applied products via irrigation. Greenhouse and field trials were conducted in Pickens County, SC, with the objectives of 1) evaluating turfgrass injury following use of POST goosegrass control options; 2) assessing if irrigating (0.6 cm) immediately following the herbicide application reduces injury of ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy]; and 3) determining if immediate irrigation influences goosegrass control at one- to three-tiller and mature growth stage. Following the application of herbicide treatments, irrigation was applied (+) or not applied (−). Treatments included the following: control (+/− irrigation); topramezone at 12.3 g a.i./ha (+/− irrigation); metribuzin at 420 g a.i./ha (+/− irrigation); and topramezone plus metribuzin (+/− irrigation) at 12.3 and 420 g a.i./ha. Irrigation treatment had minimum effect on greenhouse-grown goosegrass biomass, all treatments provided >85% control of 1- to 3-tiller goosegrass plants. However, control for mature plants was <50% for topramezone- and 60% to 70% for metribuzin-containing treatments. In field studies, at 1 week after treatment (WAT), the irrigated metribuzin and topramezone plus metribuzin had ≈37% and ≈16%, respectively, less goosegrass control vs. nonirrigated treatments. At 2WAT, irrigated metribuzin and irrigated topramezone plus metribuzin–treated plots, had ≈50% less mature goosegrass control vs. nonirrigated treatments. Irrigated herbicide treatments, however, experienced ≈23% less turfgrass injury at this time. At 4 WAT, irrigated metribuzin- and irrigated topramezone plus metribuzin–treated plots experienced reduced mature goosegrass control by ≈65% and ≈59%, respectively. Overall, incorporating POST herbicide applications via 0.6 cm of irrigation reduced turfgrass injury by at least 20% for all herbicide treatments, while maintaining goosegrass control.

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Greenhouse studies were conducted at the Univ. of Florida to evaluate the effects of preemergence herbicides on St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] rooting. Metolachlor, atrazine, metolachlor + atrazine, isoxahen, pendimethalin, dithiopyr, and oxadiazon were applied to soil columns followed by placement of St. Augustinegrass sod on the treated soil. Root elongation and biomass were measured following application. Plants treated with dithiopyr and pendimethalin had no measurable root elongation and root biomass was severely (>70%) reduced at the study's conclusion (33 days). Root biomass was unaffected following isoxaben and oxadiazon treatments, but oxadiazon applied at 3.4 kg·ha-1 reduced root length by 50%. Atrazine at 2.2 kg·ha-1 and metolachlor + atrazine at 2.2 + 2.2 kg·ha-1, did not reduce root length in one study, while the remaining atrazine and metolachlor + atrazine treatments reduced cumulative root length and total root biomass 20% to 60%. Metolachlor at 2.2 kg·ha-1 reduced St. Augustinegrass root biomass by >70% in one of two studies. St. Augustinegrass root elongation rate was linear or quadratic in response to all treatments. However, the rate of root elongation was similar to the untreated control for plants treated with isoxaben or oxadiazon. Chemical names used: 6-chloro-N-ethyl-N'-(l-methylethyl)-1,3,5-triazine-2,4-diamine(atrazine);S,S-dimethyl2-(difluoromethyl)-4-(2-methylpropyl)-6-(t∼fluoromethyl)-3,5-pyridinecarbothioate (dithiopyr); N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide (isoxaben); 2-chloro-N-(2-ethyl- 6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide (metolachlor); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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