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  • Author or Editor: Lambert McCarty x
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Spring dead spot (SDS) [Gaeumannomyces graminis (Sacc.) von Arx & D. Olivier var. graminis Walker] is a serious disease of bermudagrass [Cynodon dactylon (L.) Pers.] throughout much of the southern United States and is believed to be at least partially influenced by the previous year's turfgrass management practices. Research was performed to: a) determine the efficacy of selected fungicide control measures; and b) determine the influence of N and K nutrient regimes on the expression of SDS symptoms in Tifway bermudagrass (C. dactylon x C. transvaalensis Burtt-Davy). Averaged over two sites in 2 years, a 72% reduction in SDS followed a fall application of benomyl at 12 kg·ha. Fenarimol applied at three rates (1.5, 2.3, and 3.0 kg·ha) on three fall dates reduced SDS by a combined average of 66%. A single application of propiconazole (2.5 kg·ha) reduced disease by an average of 56%. Application of N (98 kg·ha) in late fall increased SDS 128% in one test location. Application of potassium sulfate (269 kg K/ha) in late fall resulted in an average increase in SDS expression of 89% the following spring over all experiments. Turf managers with severe SDS should minimize heavy late-fall K applications and possibly use benomyl, fenarimol, or propiconazole for disease suppression. Chemical names used: α -(2-chlorophenyl)α -(4-chlorophenyl)-S-pyrimidinemethanol (fenarimol); [methyl 1(butylcarbamoyl)-2-benzimidazolecarbamate] (benomyl); 1-[[2-(2,4-dichlorophenyl)-4propyl-1,3-dioxolan-2-yl]methyl]--1H-1,2,4-triazole (propiconazole).

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Creeping bentgrass (Agrostis palustris Huds.) is used on putting greens for its fine-leaf texture, consistent speed, smooth ball roll, and year-round color. In recent years bentgrass use has extended into the warmer climates of the southern United States. Being a C3 plant, bentgrass is not well adapted to extended hot and humid environmental conditions. Subsurface air movement systems are now commercially available that can transport air through the root zone to alter soil conditions and potentially improve bentgrass survival. This research investigated the effects of subsurface air movement on the composition of soil gases, matric potential, temperature, and growth response of a sand-based creeping bentgrass golf green. Treatments included: air movement direction (evacuate, inject, and no air) and duration of air movement (0400-0600 hr, 1000-1800 hr, and 24 hours). Treatment combinations were imposed for 13 days. Subsurface air movement reduced CO2 at the 9-cm depth to values <0.0033 mol·mol-1 when evacuating or injecting air, depending upon duration. Soil matric potentials at a 9-cm depth were decreased by a maximum of 96% when evacuating air for 24-hour duration compared to no-air plots. Soil temperatures at 9 cm were decreased ≈1 to 1.5 °C when injecting air from 1000 to 1800 hr and 24-hour treatments and increased ≈0.75 °C when evacuating air from 1000 to 1800 hr. Subsurface air movement did not improve creeping bentgrass turf quality or rooting. Although not effective in improving the growth response of creeping bentgrass, subsurface air movement may be a useful tool to improve soil gas composition, reduce excess soil moisture, and potentially reduce soil temperature(s) of heat-stressed creeping bentgrass golf greens.

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Annual bluegrass (Poa annua L.) continues to be a problem in bermudagrass golf greens overseeded with roughstalk bluegrass (Poa trivialis L. `Sabre) due to weed encroachment from adjacent fairways, lack of selective herbicide options, and weed diversity. A 2-year study was conducted on an overseeded `Tifgreen bermudagrass putting green to evaluate effects of herbicide treatments on overseeding and annual bluegrass control. Excellent annual bluegrass control (≥90%) and acceptable turfgrass cover (§70%) was achieved with oxadiazon at 2.2 kg·ha-1 a.i. applied 60 days before overseeding (DBO). Fenarimol (AS) at 4.1 kg·ha-1 a.i. (30 + 15 DBO) followed by 1.4 kg·ha-1 a.i. 60 days after overseeding (DAO) and dithiopyr at 0.6 kg·ha-1 a.i. (60 DBO + 120 DAO) also provided acceptable results. Dithiopyr at 0.4 kg·ha-1 a.i. (30 DBO + 120 DAO), dithiopyr at 0.3 kg·ha-1 a.i. (30 DBO + 30 + 120 DAO), and fenarimol (G) at 2.0 kg·ha-1 a.i. (45 + 30 DBO) followed by 0.8 kg·ha-1 a.i. 60 DAO provided inconsistent annual bluegrass control (55% to 75% in 1999 and 87% to 95% in 2000), but offered acceptable turfgrass cover (§70%) each year. The remaining treatments were generally ineffective and provided <50% annual bluegrass control one or both years. Oxadiazon applied 60 DBO at 2.2 kg·ha-1 a.i. provides an excellent option for annual bluegrass control in overseeded bermudagrass putting greens.

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Preemergence herbicides are applied to prevent summer annual weed infestations in turf, but safety to dwarf-type bermudagrass golf greens has not been determined for many of these materials. Field experiments tested ‘TifEagle’ bermudagrass response to bensulide at 11.2 kg·ha−1 (a.i.), dithiopyr at 0.56 kg·ha−1 (a.i.), napropamide at 2.2 kg·ha−1 (a.i.), oxadiazon at 2.2 kg·ha−1 (a.i.), oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 (a.i.), and pendimethalin at 1.7 kg·ha−1 (a.i.). All herbicides reduced root mass from the nontreated, but only losses incited by oxadiazon plus bensulide were acceptable (less than 20%). Dithiopyr, napropamide, and pendimethalin delayed spring greenup in 2003 and 2004, whereas oxadiazon plus bensulide delayed spring greenup in 2004. In greenhouse experiments, ‘TifEagle’ bermudagrass root mass was reduced 19% to 37%, 30% to 33%, 4% to 26%, 28% to 37%, and 24% to 30% from various rates of bensulide, dithiopyr, napropamide, and pendimethalin, respectively. Oxadiazon and oxadiaxon plus bensulide reduced root mass by only 2% to 15% and 15% to 22%, respectively. In another experiment, oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 did not injure shoots or roots of ‘Champion’, ‘FloraDwarf’, ‘MiniVerde’, ‘Tifdwarf’, or ‘TifEagle’ bermudagrass. Overall, dwarf-type bermudagrass golf greens do not appear to tolerate mitotic inhibitor preemergence herbicides, whereas oxadiazon or oxadiazon plus bensulide caused minimal injury.

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Centipedegrass [Eremochloa ophiuroides (Munro) Hack.] is widely grown throughout the southeastern United States as a low-maintenance turfgrass; however, limited peer-reviewed research is available on “best” cultural practices for established centipedegrass. This research was conducted to examine the long-term effects of mowing height and fertility regimens providing various rates and application times of soil-applied granular Fe and N on centipedegrass quality and surface coverage. Soil type was a Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludult) with a pH of 5.5. A mowing height of 3.8 cm was equal to or better than the 1.9 cm mowing height throughout the study. The rate of N fertilization played an important role in achieving optimal turfgrass quality and coverage with the two highest rates (97.6 and 195.2 kg·ha−1 N), generally providing similar results when applied as split applications in May and August and mowed at 3.8 cm. These treatments provided turfgrass quality ratings of 8.3–9.0, turfgrass color ratings of 8.1–8.7, and turfgrass coverage of 94% to 98% over a 3-year period. The addition of soil-applied Fe sulfate at a rate of 24.4 kg·ha−1 Fe was not beneficial to centipedegrass performance or color. Results indicate that the addition of 97.6 kg·ha−1 N, using split-applications in May and August and a mowing height of 3.8 cm for established centipedegrass, should achieve acceptable turfgrass quality and coverage.

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Abstract

Field experiments were conducted with the objective of determining the response of tall fescue (Festuca arundinacea Schreb.‘CIemfine’) to various amounts of single and sequential treatments of sethoxydim and fluazifop at 0.10, 0.20, or 0.30 kg·ha-1 and xylafop, haloxyfop, fenoxaprop, and poppenate at 0.07, 0.15, or 0.30 kg·ha-1 These herbicides are known to control grass weeds such as crabgrass (Digitaria spp.) and goosegrass [Eleusine indica (L.) Gaertn.] Turf color was acceptable following single and sequential fenoxaprop applications through 49 days after treatment (DAT). Turf density was not affected by single applications, but was slightly reduced by sequential applications. Single and sequential applications of poppenate provided acceptable turf color in 1985, except at 14 DAT at the high rate. In 1987, turf color was acceptable at 49 DAT. Turf density was reduced with the 0.30 kg·ha-1 single poppenate application. Sequential applications of poppenate also reduced turf density. Fenoxaprop provided acceptable turf color and density for either single or sequential applications, while poppenate provided acceptable turf color for single application at 49 DAT. Unacceptable turf color and density were observed for both years with single and sequential applications of fluazifop, sethoxydim, haloxyfop, and xylafop. Chemical names used: 2-[1-(ethoxyimino)buty]–5–[2–(ethylthio)propyl]–3–hydroxy–2–cyclohexen–1–one (sethoxydim); (±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxylphenoxy]propanoic acid (fluazifop); 2-[4-[[3-chloro-5-(trifluoromethyl)–2–pyridinyl]–propanoic acid (haloxyfop); (2-[4-[(6-chloro-2-quinoxalinyl)-oxy]phenoxyl]propanoic acid (xylafop); (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid (fenoxaprop); and methyl 3-hydroxy-4-[4-[[5–(trifluoromethyl)–2–pyridinyl]oxy]phenoxy]–pentanoate (poppenate).

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Increased soil moisture and temperature along with increased soil microbial and root activity during summer months elevate soil CO2 levels. Although previous research has demonstrated negative effects of high soil CO2 on growth of some plants, little is known concerning the impact high CO2 levels on creeping bentgrass (Agrostis palustris Huds.). The objective of this study was to investigate effects of varying levels of CO2 on the growth of creeping bentgrass. Growth cells were constructed to U.S. Golf Association (USGA) greens specification and creeping bentgrass was grown in the greenhouse. Three different levels of CO2 (2.5%, 5.0%, and 10.0%) were injected (for 1 minute every 2 hours) into the growth cells at a rate of 550 cm3·min-1. An untreated check, which did not have a gas mixture injected, maintained a CO2 concentration <1%. Gas injection occurred for 20 days to represent a run. Two runs were performed during the summer of 1999 on different growth cells. Visual turf quality ratings, encompassing turf color, health, density, and uniformity, were evaluated every 4 days on a 1-9 scale, with 9 = best turf and <7 being unacceptable. Soil cores were taken at the end of each run. Roots were separated from soil to measure root depth and mass. Turf quality was reduced to unacceptable levels with 10% CO2, but was unaffected at lower levels over the 20-day treatment period. Soil CO2 ≥2.5% reduced root mass and depth by 40% and 10%, respectively.

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Dwarf-type bermudagrass (Cynodon dactylon Pers. × C. transvaalensis Burtt-Davy) putting greens tolerate long-term mowing heights of 3.2 mm but require heavy nitrogen (N) fertilizations that increase ball roll resistance. Applying a plant growth regulator, such as trinexapac-ethyl (TE), could reduce uneven shoot growth from high N fertility and improve putting green ball roll distances. Field experiments were conducted from April to August 2003 and 2004 in Clemson, SC to investigate effects of ammonium nitrate applied at 6, 12, 18, or 24 kg N/ha per week with TE applied at 0 or 0.05 kg a.i. per ha every 3 weeks on `TifEagle' bermudagrass ball roll distances (BRD). BRD were measured weekly with a 38-cm stimpmeter in the morning (900 to 1100 hr) and evening (>1700 hr) beginning 1 wk after initial TE treatments. Interactions were not detected among N, TE, or time of day. TE increased BRD about 15% from non-TE treated. BRD was reduced with increased N rate and from am to pm; however, bermudagrass treated with TE averaged 10% longer PM BRD than am distances of non-TE treated. Overall, increased N fertility and diurnal shoot growth may reduce BRD but TE will be an effective tool for mitigating these effects on bermudagrass putting greens. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl).

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As golfers demand higher quality golf green putting surfaces, researchers continue to seek improved turfgrass cultivars. One such improved cultivar is `TifEagle' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], which is an improvement over traditional bermudagrass cultivars such as `Tifgreen' and `Tifdwarf' due to its ability to tolerate mowing heights of ≤3.2 mm for extended periods. One observed disadvantage of `TifEagle' is its lack of a deep, dense root system compared to previous bermudagrass cultivars. This field study measured mowing height, N rate, and biostimulant product effects on `TifEagle' rooting. Three mowing heights (3.2, 4.0, and 4.8 mm), three N rates (12, 24, and 48 kg N/ha/week), and two cytokinin-containing commercial biostimulant products (BIO1 and BIO2) were examined. Plant responses measured were root length density (RLD), root surface area (RSA), thatch layer depth (TLD), and turf quality (TQ). Increasing mowing height from 3.2 to 4.0 mm increased RLD by >11%, RSA by >11%, and TQ by >17%. Increasing N rates from 12 to 24 kg N ha-1 week-1 increased RLD by >17%, RSA by >26% and TQ by >16%. No effect on RLD was observed after the first year of biostimulant use, however, after the second year, BIO1 increased RLD by >11% when applied with the lowest rate of N (12 kg N/ha/week). Higher mowing heights (4.8 and 4.0 mm) increased TLD >6% compared to the lowest mowing height (3.2 mm), and higher N rates (48 and 24 kg N/ha/week) increased TLD >3% compared to the lowest N rate (12 kg N/ha/week). Overall, a mowing heights ≥4.0 mm, N rates ≥24 kg N/ha/week, and long-term use of a cytokinins-containing biostimulant had a positive effect on `TifEagle' rooting.

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Studies on bermudagrasses (Cynodon spp.) have demonstrated variability in salinity response among species and cultivars. However, information on ultradwarf bermudagrass cultivars in relative salinity tolerance associated with trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester], a cyclohexanedione type II plant growth regulator (PGR), remains unknown. Therefore, two replicated greenhouse studies were conducted to determine the salinity tolerance of two ultradwarf bermudagrass cultivars treated with TE on turfgrass quality (TQ), total root biomass, and root and shoot tissue nutrient concentration. Turfgrasses included `TifEagle' and `Champion' bermudagrass (Cynodondactylon(L.) Pers. × C. transvaalensisBurtt-Davy). Daily sodium chloride (NaCl) exposure was 0, 12.90 (8,000 ppm), 25.80 (16,000 ppm), and 38.71 dS·m–1 (24,000 ppm). Biweekly TE applications (active ingredient 0.02 kg·ha–1) were initiated 2 weeks after salinity exposure. `Champion' was more salt-tolerant than `TifEagle' based on TQ and root mass. At 12.90, 25.80, and 38.71 dS·m–1 of NaCl, nontreated (without TE) `Champion' consistently outperformed nontreated `TifEagle' with greater TQ on most rating dates. At 12.90 dS·m–1, TE treated `Champion' (8.0) had greater TQ than nontreated `TifEagle' (6.1) at week 10. Regardless of TE application, after 2 weeks of applying 25.80 dS·m–1 of NaCl, both cultivars fell below acceptable TQ (<7). When averaged across all salinity treatments, applying TE four times at 0.02 kg·a.i./ha in two week intervals enhanced root growth for both bermudagrass cultivars by 25%. Also, both cultivars decreased root mass as salinity levels increased. Non TE-treated `TifEagle' had 56% and 40% less root and shoot Na uptake compared to TE treated cultivars at 25.80 dS·m–1. In conclusion, the two bermudagrass cultivars responded differently when exposed to moderate levels of NaCl.

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