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Patrick E. McCullough and William Nutt

Turf managers may wish to reseed common bermudagrass [Cynodon dactylon (L.) Pers.] following weed control with rimsulfuron, simazine, or sulfosulfuron applications, but establishment may be affected by herbicide residual activity. Field experiments were conducted in Georgia to investigate bermudagrass reseeding intervals for these herbicides. Application timing before seeding reduced bermudagrass establishment more than herbicide rate. By four weeks after seeding, bermudagrass cover was 15%, 53%, 81%, and 90% of the untreated from herbicides applied zero, two, four, or six weeks before seeding, respectively. Simazine at 2.24 kg a.i./ha reduced bermudagrass cover more frequently than sulfosulfuron at 0.035 and 0.07 kg a.i./ha and rimsulfuron at 0.02 kg a.i./ha. Results suggest that common bermudagrass may be safely reseeded four to six weeks after rimsulfuron, simazine, or sulfosulfuron treatments, but applications made closer to the seeding date have the potential to significantly delay establishment.

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Thomas V. Reed and Patrick E. McCullough

Swinecress [Coronopus didymus (L.) Sm.] is a problematic weed in newly seeded tall fescue (Festuca arundinacea Schreb.) and often warrants control with herbicides. The objective of this research was to investigate the influence of application timing on efficacy of aminocyclopyrachlor, fluroxypyr, and triclopyr for swinecress control compared with dichlorophenoxyacetic acid (2,4-D) + 3,6-dichloro-o-anisic acid (dicamba) + methylchlorophenoxypropionic acid (MCPP). Aminocyclopyrachlor at 0.05 and 0.10 kg a.i./ha provided less than 35% control from February applications, but both rates averaged greater than 90% control with April applications. Fluroxypyr at 0.26 and 0.52 kg a.i./ha provided poor (less than 70%) control from February applications but control increased to 71% and 90% from April treatments, respectively. Triclopyr at 0.56 and 1.12 kg a.i./ha provided greater than 90% swinecress control at both application timings and was comparable to 2,4-D + dicamba + MCPP. Overall, aminocyclopyrachlor and fluroxypyr were only effective for controlling swinecress in April, whereas triclopyr provided excellent control with February and April applications.

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Diego Gómez de Barreda, Jialin Yu, and Patrick E. McCullough

Grassy weeds may reduce cool-season turfgrass establishment after seeding and herbicide use is often warranted. Field experiments were conducted to evaluate the tolerance of creeping bentgrass (Agrostis stolonifera L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) to fenoxaprop and metamifop applications at 1, 2, 3, or 4 weeks after seeding (WAS). Creeping bentgrass groundcover was reduced from 34% to 71% at 8 WAS from the nontreated by fenoxaprop at 50 g a.i./ha and metamifop at 400 and 800 g a.i./ha at all application timings. Metamifop at 200 g·ha−1 reduced creeping bentgrass cover 10% to 18% from the nontreated at 8 WAS when applied 1, 2, or 3 WAS, but treatments at 4 WAS did not reduce cover. Perennial ryegrass treated with fenoxaprop and metamifop at 800 g·ha−1 at 1 WAS had cover reduced from the nontreated on two and one dates, respectively, whereas tall fescue cover was never reduced greater than 5% from the nontreated. Results suggest applications to creeping bentgrass should be delayed greater than 4 WAS for fenoxaprop at 50 g·ha−1, greater than 4 WAS for metamifop at 400 and 800 g·ha−1, and 3 WAS for metamifop at 200 g·ha−1. Additionally, fenoxaprop applications should be delayed 2 WAS for perennial ryegrass and tall fescue, whereas metamifop could be safely applied at all rates at 1 WAS.

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Plant growth regulators (PGRs) are commonly used to enhance putting green quality and ball roll distances but their effects with various mowing operations have not been reported. Three experiments were conducted and repeated at Clemson University, Clemson, SC, on an `L-93' creeping bentgrass putting green to evaluate the effects of mowing operations and PGRs on diurnal ball roll distances. The PGRs tested included ethephon at (a.i.) 3.8 kg·ha-1, flurprimidol at (a.i.) 0.28 kg·ha-1, paclobutrazol at (a.i.) 0.28 kg·ha-1, and trinexapac-ethyl at (a.i.) 0.05 kg·ha-1. Mowing operations tested included rolling vs. mowing, morning mowing vs. morning plus afternoon mowing, and single vs. double morning mowing, all with and without PGRs. PGR by mowing operation interactions did not occur in any experiments. Ball roll distances decreased from 12:00 hr to evening observations in all experiments. In Experiment 1, rolling the green without mowing reduced ball roll distance 4% (5 cm) compared to mowing. Turf rolled without mowing in the morning and treated with flurprimidol, paclobutrazol, and trinexapac-ethyl produced similar ball roll at 12:00, 15:00, and 18:00 hr to mowed untreated turf. In Experiment 2, all plots were mowed at 08:00 hr and half of each plot was remowed at 12:30 hr. The second mowing at 12:30 hr enhanced ball roll distances 6% (8 cm) over the day. Turf mowed only at 08:00 and treated with paclobutrazol and trinexapac-ethyl had greater or equal ball roll distances at 12:30, 15:30, and 18:30 hr to untreated turf that had a second mowing at 12:30 hr. Turf receiving ethephon and 08:00 hr mowing had 4% to 12% (4 to 17 cm) shorter ball roll distances throughout the day compared to untreated turf mowed at 8:00 and 08:00+12:30 hr, respectively. In the third experiment, mowing twice in the morning increased ball roll 3% (4 cm) compared to mowing once. Trinexapac-ethyl and paclobutrazol treated turf mowed once in the morning had greater or equal ball roll distances throughout the day to untreated turf mowed twice in the morning. Overall, PGR use may provide putting green ball roll distances similar to or greater than untreated turf despite additional mowing; however, ethephon reduced ball roll distances regardless of mowing operations. Chemical names used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol} (flurprimidol); (+/-)-(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol); [(2-chloroethyl)phosphonic acid] (ethephon).

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Patrick E. McCullough, James T. Brosnan, and Gregory K. Breeden

Turf managers applying amicarbazone for annual bluegrass (Poa annua L.) control in cool-season turfgrasses may wish to reseed into treated areas. Field experiments were conducted in Georgia and Tennessee to investigate perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) reseeding intervals after amicarbazone applications. Perennial ryegrass and tall fescue cover were reduced similarly (less than 10% from the untreated) by all herbicides applied 2, 4, or 6 weeks before seeding. Bispyribac-sodium at 0.1 kg a.i./ha reduced tall fescue and perennial ryegrass cover more than amicarbazone at 0.1 or 0.2 kg a.i./ha when applied the day of seeding. Applied on the day of seeding in Georgia, amicarbazone at 0.4 kg·ha−1 reduced turf cover of each species similar to bispyribac-sodium; however, this response was not observed in Tennessee. Results suggest tall fescue and perennial ryegrass can be safely seeded the day of amicarbazone applications at 0.1 or 0.2 kg·ha−1, but practitioners may need to wait 2 weeks before seeding these turfgrasses into areas treated with amicarbazone at 0.4 kg·ha−1 or bispyribac-sodium at 0.1 kg a.i./ha.

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Trinexapac-ethyl (TE) is an effective plant growth retardant for hybrid bermudagrass; however, growth responses of various dwarf-type bermudagrass cultivars to TE have not been reported. Two 60-day greenhouse experiments were conducted at the Clemson Greenhouse Research Complex, Clemson, S.C., to evaluate the response of `Champion', `FloraDwarf', `MiniVerde', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass with and without TE at 0.0125 kg·ha-1 a.i. per 10 days. From 20 to 60 days after initial treatments, TE enhanced visual quality 9% to 13% for all cultivars. From four samples, TE reduced clippings 63%, 63%, 69%, 62%, 64%, and 46% for `Champion', `FloraDwarf', `MiniVerde', `Tifdwarf', and `TifEagle', respectively. Trinexapac-ethyl enhanced root mass 23% and 27% for `MiniVerde' and `FloraDwarf' bermudagrass, respectively. `Champion', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass treated with TE had similar root mass to the untreated respective cultivars. Among untreated cultivars, `FloraDwarf', `MiniVerde', `MS Supreme', and `Tifdwarf' had similar root masses; however compared to these cultivars, `Champion' and `TifEagle' had 33% and 81% less root mass, respectively. Root length was unaffected by TE; however, `Champion' and `TifEagle' averaged 20% and 36% less root length compared to `Tifdwarf' bermudagrass, respectively, while `FloraDwarf', `MiniVerde', and `MS Supreme' had similar root length to `Tifdwarf'. Trinexapac-ethyl safely enhanced turf quality and reduced clipping yield at 0.0125 kg·ha-1 per 10 days without inhibiting root growth of six dwarf-type bermudagrasses. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl).

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Trinexapac-ethyl (TE) is a plant growth regulator registered for periodic applications on creeping bentgrass greens but ball roll as affected by various TE regimens have not been reported. Field experiments were conducted in Clemson, S.C., from May to July 2003 and 2004 on an `L-93' creeping bentgrass putting green. Turf received a total of 0.2 kg·ha–1 a.i. of TE over 12 weeks in three application regimens: 0.017 kg·ha–1 per week, 0.033 kg·ha–1 per 2 weeks, and 0.05 kg·ha-1 per 3 weeks plus a control. Ball roll distances were measured weekly with a stimpmeter in the morning (900 to 1100 hr) and evening (>1700 hr). Morning ball roll distances were generally longer than evening. Ball roll distances increased from June to July 2003 and from May to July 2004, likely resulting from greater bentgrass summer heat stress during the test period. Turf treated with biweekly and triweekly TE regimens had enhanced ball roll on three and four dates, respectively, but inconsistencies occurred likely from reduced efficacy with greater time between repeated applications. Weekly TE applications enhanced ball roll distances from the untreated by 5% to 8% on six dates. Turf injury did not occur following TE applications regardless of regimen. Overall, weekly TE applications increased ball roll distances more frequently than biweekly and triweekly regimens, but enhancements were inconsistent over the 2 years. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl); (tetrachloroisophthalonitrile) (chlorothalonil); [methyl(E)-2-(2-(6-(2-cyanophenoxy) pyrimidin-4-yloxy)phenyl)-3-methoxyacrylate] (azoxystrobin); [aluminum tris(0-ethyl phosphonate)] (fosetyl-al); [N-(2,6-Dimethylphenyl)-N-(methoxyacetyl) alanine methyl ester] (metalaxyl); [(1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl) -methyl]-14-1,2,4-triazole] (propiconazole).

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Ethephon is an effective growth retardant for suppressing Poa annua (L.) seedheads in creeping bentgrass putting greens; however, ethylene induction may cause bentgrass leaf chlorosis, reduced rooting, and quality decline. Two greenhouse experiments investigated the effects of nitrogen (N) fertility and ethephon applications on `L-93' creeping bentgrass over 9 weeks. Ethephon was applied at 0, 3.8, and 7.6 kg·ha–1 a.i. per 3 weeks and N was applied at 4 and 8 kg·ha–1·week–1. Ethephon applications linearly reduced bentgrass quality on every weekly observation. Increased N rate to 8 kg·ha–1·week–1 improved turf quality about 10% to 20% and 10% to 30% from ethephon applied at 3.8 and 7.6 kg·ha–1 per 3 weeks, respectively. Increased N rate to 8 kg·ha–1·week–1 enhanced shoot growth 30% but reduced root mass and length 12% and 11%, respectively. After 9 weeks, ethephon reduced root length by about 30% and root mass about 35% at both rates. From nine weekly samples, ethephon reduced dry clipping yield 10% and 16% at 3.8 and 7.6 kg·ha–1 per 3 weeks, respectively. From 2 to 9 weeks after initial treatments, ethephon linearly increased leaf water content. Increasing N fertility effectively reduced bentgrass leaf chlorosis from ethephon; however, repeat applications of ethephon and increased N may restrict bentgrass root growth. Chemical names used: [(2-chloroethyl)phosphonic acid] (ethephon).

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Plant growth regulators are applied to inhibit uneven shoot growth of putting green turf but research is limited on responses of dwarf-type bermudagrass cultivars to growth inhibition. Experiments were conducted at the Clemson University Greenhouse Complex with `Champion' and `TifEagle' bermudagrass grown in polyvinylchloride containers with 40 cm depths and 177 cm2 areas built to United States Golf Association specification. Flurprimidol was applied at 0.14, 0.28, and 0.48 kg·ha–1 a.i. and paclobutrazol at 0.14 kg·ha–1 a.i. on separate containers. Flurprimidol at 0.28 and 0.42 kg·ha-1 caused 17% and 31% reduction in turf color 5 weeks after treatment (WAT), respectively. `Champion' exhibited unacceptable turf injury (>30%) 2 WAT from paclobutrazol and all flurprimidol rates. `TifEagle' had unacceptable turf injury from flurprimidol at 0.42 kg·ha–1 2 WAT, 0.28 kg·ha–1 3 WAT, and 0.14 kg·ha–1 4 WAT that did not recover. Moderate injury (16% to 30%) was observed from paclobutrazol on `TifEagle' but ratings were acceptable. After 6 weeks, flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1 reduced bermudagrass green shoot density (GSD) per square centimeter by 20%, 40%, and 40%, respectively, while paclobutrazol reduced GSD 12%. `TifEagle' total clipping yield was reduced 60%, 76%, and 86% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 37% from paclobutrazol. `Champion' total clipping yield was reduced 82%, 90%, and 90% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 58% from paclobutrazol. After 6 weeks, flurprimidol reduced `Champion' total root mass by 44% over all three rates. `Champion' treated with paclobutrazol had similar total root mass to the untreated. `TifEagle' treated with all PGRs had similar rooting to the untreated. Overall, flurprimidol will likely not be suitable for dwarf bermudagrass maintenance at these rates; however paclobutrazol may have potential at ≤0.14 kg·ha–1. Chemical names used: Flurprimidol {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol}; Paclobutrazol, (+/-)–(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol.

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Patrick E. McCullough, Ted Whitwell, Lambert B. McCarty, and Haibo Liu

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.