Travis W. Gannon

Efficacy of Application Placement Equipment for Tall Fescue (Lolium Arundinaceum) Growth and Seedhead Suppression

Field research was conducted to evaluate plant growth-regulator efficacy for tall fescue growth and seedhead suppression applied using application placement equipment. Specially designed equipment outfitted with fluid application systems applies low-volume plant growth regulator directly on plant foliage, reducing opportunity for drift and visible application. Wet-blade mowers are equipped to apply plant growth regulators and mow in a single pass, whereas rotary-wick applicators simply wipe chemicals directly on uncut vegetation. Therefore, a wet-blade, rotary-wick, and broadcast sprayer system were chosen to apply imazapic at three rates (9, 35, and 53 g ai/ha), and a mefluidide + chlorsulfuron tank mix at 7 + 140 g ai/ha to tall fescue roadsides for vegetative growth and seedhead suppression. Experiments were conducted during the spring and summer of 2004 in central and western North Carolina. Tall fescue was slightly injured and discolored by all treatments but fully recovered by 2 mo after treatment. Imazapic suppressed new vegetative growth 3 mo after treatment compared with the nonmowed–nontreated control (16.1 cm of growth) and the mowed–nontreated control (21.1 cm) when applied with the rotary-wick applicator (8.5 cm) and broadcast sprayer (6.2 cm). However, differences in vegetative height primarily occurred when application placement equipment treatments were compared with nontreated vegetation as opposed to mowed–nontreated plants. Although mowed–nontreated and wet-blade–treated plots had more new vegetative growth, nonmowed–nontreated plots still consistently had the greatest vegetative height. Seedhead suppression ranged from 87 to 100% when compared with the nonmowed–nontreated control, with wet-blade treatments consistently providing the least-effective seedhead suppression. Overall, application placement equipment did not improve plant growth-regulator efficacy when compared with the foliar broadcast spray. Nomenclature: Chlorsulfuron; imazapic; mefluidide; tall fescue, Lolium arundinaceum (Schreb.) S.J. Darbyshire, ‘Kentucky 31’

Response of Four Improved Seeded Bermudagrass Cultivars to Postemergence Herbicides during Seeded Establishment

Herbicides and herbicide prepackaged mixtures registered for use on established bermudagrass turf may cause significant injury to recently seeded bermudagrass cultivars, delaying full establishment. Research was conducted to evaluate the use of 12 herbicide treatments applied at onset of uniform stolon development (4 to 8 wk after seeding) to recently seeded ‘Princess 77,’ ‘Riviera,’ ‘Savannah,’ and ‘Yukon’ bermudagrass cultivars. In general, Yukon was more susceptible to herbicide injury than other cultivars. Atrazine at 1.1 kg ai/ha injured all cultivars 55 to 59% 14 d after initial treatment (DAIT), which lead to reduced bermudagrass cover 21 DAIT. Triclopyr + clopyralid at 0.63 + 0.21 kg ae/ha, respectively, injured Savannah and Yukon greater than other broadleaf weed herbicides (2,4-D + mecoprop + dicamba or 2,4-D + clopyralid + dicamba). Foramsulfuron did not injure or reduce bermudagrass cover of any cultivar evaluated at any rating date. The only adverse effect of trifloxysulfuron was a reduction in Riviera and Yukon ground cover at 21 DAIT. MSMA applied sequentially and quinclorac treatments did not injure or reduce ground cover of Savannah or Princess 77. MSMA applied sequentially and/or quinclorac injured and reduced ground cover of Riviera and Yukon; however, both cultivars completely recovered from MSMA or quinclorac injury by 42 DAIT. Nomenclature: clopyralid, 2,4-D, dicamba, foramsulfuron, mecoprop, MSMA, triclopyr, trifloxysulfuron, quinclorac; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA, ‘Princess 77’, ‘Riviera’, ‘Savannah’, ‘Yukon.’ Additional index words: Seeded establishment, stolon development, turfgrass tolerance. Abbreviations: DAIT, days after initial treatment; NTEP, National Turfgrass Evaluation Program.

Foliar vs. Soil Exposure of Green Kyllinga (Kyllinga brevifolia) and False-Green Kyllinga (Kyllinga gracillima) to Postemergence Treatments of CGA-362622, Halosulfuron, Imazaquin, and MSMA1

Greenhouse studies were conducted to evaluate shoot number, shoot weight, rhizome weight, and root weight reduction of green and false-green kyllinga at three placement levels (soil applied, foliar applied, and soil + foliar applied) and five herbicide treatments (CGA-362622, halosulfuron, imazaquin, MSMA, and imazaquin + MSMA). Averaged over herbicide and placement level, false-green kyllinga shoot number 30 d after treatment (DAT) and rhizome weight 60 DAT were reduced more than those of green kyllinga. Furthermore, imazaquin, MSMA, and imazaquin + MSMA, averaged across placement levels, as well as CGA-362622 and halosulfuron, both foliar and soil applied, reduced false-green kyllinga shoot number greater than that of green kyllinga 60 DAT. Halosulfuron reduced false-green kyllinga shoot weight greater than that of green kyllinga 60 DAT; however, MSMA reduced green kyllinga greater. In general, foliar- and soil + foliar–applied treatments reduced shoot number (30 DAT), rhizome weight, and root weight of both kyllinga species greater than soil-applied treatments, whereas soil + foliar–applied treatments were more effective in reducing shoot weight 60 DAT. CGA-362622 and halosulfuron reduced kyllinga species shoot number (30 DAT), false-green kyllinga shoot weight (60 DAT), and root weight of both species greater than all other herbicides. However, CGA-362622 reduced green kyllinga shoot weight (60 DAT) and rhizome weight of both species greater than all other herbicides. Nomenclature: CGA-362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluroethoxy)- pyridin-2-sulfonamide sodium salt; halosulfuron; imazaquin; MSMA; false-green kyllinga, Kyllinga gracillima L.; green kyllinga, Kyllinga brevifolia Rottb. #3 KYLBR. Additional index words: Foliar absorption, root absorption. Abbreviations: ALS, acetolactate synthase; DAP, days after planting; DAT, days after treatment; NIS, nonionic surfactant; POST, postemergence.

Control of Silvery-Thread Moss (Bryum argenteum Hedw.) in Creeping Bentgrass (Agrostis palustris Huds.) Putting Greens1

Field experiments were conducted to evaluate chemicals for silvery-thread moss control and bentgrass turfgrass quality. Treatments included iron (Fe)-containing products, nitrogen fertilizers, Ultra Dawn dishwashing detergent (UD) at 3% (v/v), and oxadiazon. In general, greater silvery-thread moss control was achieved with Fe-containing products. Ferrous sulfate at 40 kg Fe/ha plus ammonium sulfate at 30 kg N/ha, a combined product of ferrous oxide, ferrous sulfate, and iron humates (FEOSH) at 125 kg Fe/ha, and a combined product of iron disulfide and ferrous sulfate (FEDS) at 112 kg Fe/ha reduced silvery-thread moss populations 87, 81, and 69%, respectively, 6 wk after initial treatment (WAIT). UD reduced silvery-thread moss populations 57% 6 WAIT. The addition of oxadiazon to Fe-containing treatments did not improve silvery-thread moss population reduction. Other experiments evaluated two formulations of chlorothalonil, each applied at two rates, chlorothalonil with zinc at 9.5 and 17.4 kg ai/ha and chlorothalonil without zinc at 9.1 and 18.2 kg/ ha, and two spray volumes (2,038 and 4,076 L/ha). Greater silvery-thread moss population reduction was observed at Jefferson Landing in 1999 compared with Elk River in 1999 and 2000. Rainfall events at Elk River in 1999 and 2000 within 24 h after application and no rain at Jefferson Landing may account for variation in performance of products between sites. However, no difference in chlorothalonil formulation, rate, or spray volume was observed in any location or year. These data indicate that Fe-containing fertilizers or chlorothalonil can be used to reduce silvery-thread moss populations in creeping bentgrass putting greens. Nomenclature: Chlorothalonil, tetrachloroisophthalonitrile; oxadiazon; silvery-thread moss, Bryum argenteum Hedw.; creeping bentgrass, Agrostis palustris Huds. ‘Penncross’. Additional index words: Bryology, moss control, turfgrass injury. Abbreviations: BM, Black Mountain Golf Club; ER, Elk River Country Club; JL, Jefferson Landing Golf Club; MNP, micronutrient package; NPK, 20:20:20 nitrogen–phosphorus–potassium; UD, Ultra Dawn dishwashing detergent; WAIT, weeks after initial treatment.

Arsenic Retention in Foliage and Soil after Monosodium Methyl Arsenate (MSMA) Application to Turfgrass.

Monosodium methyl arsenate (MSMA) is a commonly used herbicide for weed control in turfgrass systems. There is concern that arsenic from applied MSMA could leach to groundwater or run off into surface water, thereby threatening human and ecosystem health. The USEPA has proposed a phase-out of the herbicide but is seeking additional research about the toxicity and environmental impacts of MSMA before establishing a final ruling. Little research has systematically investigated MSMA in field-based settings; instead, risks have been inferred from isolated field measurements or model-system studies. Accordingly, the overall goal of this study was to quantify the fate of arsenic after MSMA application to a managed turfgrass system. After MSMA application to turfgrass-covered and bareground lysimeters, the majority of arsenic was retained in turfgrass foliage and soils throughout year-long experiments, with 50 to 101% of the applied arsenic recovered in turfgrass systems and 55 to 66% recovered in bareground systems. Dissolved arsenic concentrations from 76.2-cm-depth pore water in the MSMA-treated soils were consistently <2 μg L, indistinguishable from background concentrations. As measured by adsorption isotherm experiments, MSMA retention by the sandy soil from our field site was markedly less than retention by a washed sand and a clay loam. Collectively, these results suggest that under aerobic conditions, minimal arsenic leaching to groundwater would occur after a typical application of MSMA to turfgrass. However, repeated MSMA application may pose environmental risks. Additional work is needed to examine arsenic cycling near the soil surface and to define arsenic speciation changes under different soil conditions.

Evaluating Multiple Rating Methods Utilized in Turfgrass Weed Science

Abstract Turfgrass weed scientists commonly use visual ratings (VR) to assign a numerical value to a turfgrass or weed response. These ratings lack quantifiable numerical values and are considered subjective. Alternatives to VR, including line intersect analysis (LIA) and digital image analysis (DIA), have been used to varying extents in turfgrass research. Alternatives can be expensive, labor intensive, and can require extensive calibration and increased time for data acquisition. Minimal research has been conducted evaluating rating methods used in turfgrass weed science. Trials were conducted in 2007 and 2008 to evaluate ratings methods used to quantify large crabgrass populations as influenced by tall fescue mowing height (2.5, 5.1, 7.6, and 10.2 cm). Percent large crabgrass cover was assessed utilizing VR, LIA, and DIA to determine if differences existed among evaluation methods. Pairwise comparisons, Pearsons correlation, and linear regression were performed to compare evaluations. All rating methods were significantly correlated to one another. Differences of large crabgrass cover estimates existed between LIA and DIA data at all mowing heights and between VR and DIA data at the 7.6 and 10.2 cm mowing heights in 2007. Authors believe that shadows produced by the turf canopy at higher (≥ 7.6 cm) mowing heights increased DIA estimates of large crabgrass cover. At trial initiation in 2007, researchers did not capture calibration images because the methodology to eliminate a shadow influence using a standard digital image had not been published. Additional DIA calibration in 2008 corrected for canopy shadows, and no differences were observed in large crabgrass cover between all evaluation methods indicated by nonsignificance pairwise comparisons and estimated regression parameters. These data indicate VR are no different than LIA or DIA in estimating large crabgrass cover as affected by tall fescue mowing height. Nomenclature: Tenacity (mesotrione); large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; tall fescue, Lolium arundinaceum (Schreb.) S. J. Darbyshire. Resumen Los científicos de malezas en céspedes usan estimaciones visuales (VR) para asignar un valor numérico a las respuestas del césped o de la maleza. Estas estimaciones carecen de valores numéricos cuantificables y son consideradas subjetivas. Las alternativas a VR incluyen el análisis de intersección de líneas y análisis digital de imágenes (DIA), que han sido usados en diferentes niveles en la investigación en céspedes. Las alternativas pueden ser costosas, intensivas en labor, y pueden requerir una calibración extensiva e incrementos en el tiempo de adquisición de datos. La investigación que se ha realizado ha sido mínima para evaluar los métodos de evaluación usados en la ciencia de malezas en céspedes. Se realizaron estudios en 2007 y 2008 para evaluar los métodos de evaluación usados para cuantificar poblaciones de Digitaria sanguinalis a su vez que la influencia de la altura de poda en Lolium arundinaceum.(2.5, 5.1, 7.6 y 10.2 cm). El porcentaje de cobertura de D. sanguinalis fue evaluado utilizando VR, LIA y DIA para determinar la existencia de diferencias entre estos métodos de evaluación. Comparaciones de pares, correlación Pearson, y regresión lineal fueron realizadas para comparar los diferentes métodos. Todos los métodos de evaluación correlacionaron entre ellos en forma significativa. Hubo diferencias en la cobertura de D. sanguinalis entre los datos de LIA y DIA en todas las alturas de poda y entre los datos de VR y DIA a alturas de 7.6 y 10.2 cm en 2007. Los autores creen que las sombras producidas por el dosel del césped a alturas de poda altas (≥7.6 cm) incrementó los estimados de DIA de la cobertura de D. sanguinalis. Al inicio del estudio en 2007, los investigadores no capturaron imágenes de calibración porque la metodología para eliminar la influencia de las sombras usando una imagen digital estándar no había sido publicada. La calibración adicional de DIA en 2008 corrigió por sombras del dosel, y no se observaron diferencias en la cobertura de D. sanguinalis entre los diferentes métodos de evaluación, lo cual fue indicado por la no-significancia de las comparaciones de pares y los parámetros de regresión estimados. Estos datos indican que VR no es diferente de LIA o DIA al estimar el porcentaje de cobertura de D. sanguinalis al ser influenciada por la altura de poda de L. arundinaceum.

Absorption, Translocation, and Metabolism of Aminocyclopyrachlor in Tall Fescue (Lolium arundinaceum)

Abstract Synthetic auxin herbicides are commonly used in forage, pasture, range, and turfgrass settings for dicotyledonous weed control. Aminocyclopyrachlor (AMCP) is a newly developed pyrimidine carboxylic acid with a chemical structure and mode of action similar to the pyridine carboxylic acids—aminopyralid, clopyralid, and picloram. Injury to sensitive dicotyledonous plants has been observed following exposure to monocotyledonous plant material previously treated with pyridine compounds. The absorption, translocation, and metabolism of AMCP has been documented in susceptible broadleaf weeds; however, no information is available, to our knowledge, regarding AMCP fate in tolerant Poaceae, which may serve as the vector for off-target plant injury. Based on this premise, research was conducted to characterize absorption, translocation, and metabolism of AMCP in tall fescue. 14C-AMCP was applied to single tiller tall fescue plant foliage under controlled laboratory conditions at North Carolina State University (Raleigh, NC). Radiation was quantified in leaf wash, treated leaf, foliage, crown, roots, and root exudates at 3, 12, 24, 48, 96, and 192 h after treatment (HAT). 14C-AMCP was rapidly absorbed by tall fescue, reaching 38 and 68% at 3 and 48 HAT, respectively. Translocation of 14C-AMCP was limited to the foliage, which reached maximum translocation (34%) at 96 HAT. Most of the recovered 14C-AMCP remained in the leaf wash, treated leaf, or foliage, whereas minimal radiation was detected in the crown, roots, or root exudates throughout the 192-h period. No AMCP metabolism was observed in tall fescue through the 192 HAT. These data suggest AMCP applied to tall fescue can remain bioavailable, and mishandling treated plant material could result in off-target injury. Nomenclature: Aminocyclopyrachlor; tall fescue, Lolium arundinaceum (Schreb.) S.J. Darbyshire.

Establishment of Seeded Centipedegrass (Eremochloa ophiuroides) in Utility Turf Areas

Experiments were conducted to evaluate safety and effectiveness of herbicides during establishment of seeded centipedegrass. Centipedegrass tolerance to herbicides was evaluated at seeding and early postemergence. Imazapic at 105 g ai/ha, sulfometuron at 53 g ai/ha, or metsulfuron at 21 or 42 g ai/ha applied at seeding reduced centipedegrass ground cover compared with the nontreated. Imazapic at 18 or 35 g/ha or applications of atrazine or simazine at seeding did not reduce centipedegrass ground cover compared with the nontreated. Applications of chlorsulfuron plus mefluidide (7 + 140 g ai/ha) or metsulfuron at 21 or 42 g/ha applied 6 wk after seeding (WAS) centipedegrass (one-leaf to one-tiller growth stage) caused 20, 16, and 83% phytotoxicity, respectively, 56 d after treatment (DAT). Imazapic, sulfometuron, atrazine, or simazine applied 6 WAS caused <15% phytotoxicity 56 DAT. When large crabgrass and centipedegrass were seeded together, large crabgrass emergence was reduced 41% when atrazine (1,100 g ai/ha) was applied at seeding. Centipedegrass tiller production was reduced with increasing amounts of crabgrass. However, centipedegrass tiller production and ground cover were higher when atrazine was applied because of reduced interspecific interference from large crabgrass. These data indicate that centipedegrass can be established more quickly if appropriate herbicides are used at seeding or shortly after seeding. Nomenclature: Atrazine; chlorsulfuron; imazapic; mefluidide; metsulfuron; simazine; sulfometuron; large crabgrass, Digitaria sanguinalis (L.) Scop. #3 DIGSA; centipedegrass, Eremochloa ophiuroides (Munro) Hack. Additional index words: Atrazine, chlorsulfuron, Digitaria sanguinalis, herbicide tolerance, imazapic, interference, large crabgrass, mefluidide, metsulfuron, PGR tolerance, simazine. Abbreviations: DAS, days after seeding; DAT, days after treatment; PGR, plant growth regulator; WAS, weeks after seeding.

Sorption of Simazine and S-Metolachlor to Soils from a Chronosequence of Turfgrass Systems

Abstract Pesticide sorption by soil is among the most sensitive input parameters in many pesticide-leaching models. For many pesticides, organic matter is the most important soil constituent influencing pesticide sorption. Increased fertility, irrigation, and mowing associated with highly maintained turfgrass areas result in constant deposition of organic material, creating a soil system that can change drastically with time. Changes in soil characteristics could affect the environmental fate of pesticides applied to turfgrass systems of varying ages. Sorption characteristics of simazine and S-metolachlor were determined on five soils from bermudagrass systems of increasing ages (1, 4, 10, 21, and 99 yr) and compared to adjacent native pine and bare-ground areas. Surface soil (0 to 5 cm) and subsurface soil (5 to 15 cm) from all sites were air-dried and passed through a 4-mm sieve for separation from plant material. Using a batch-equilibrium method, sorption isotherms were determined for each soil. Data were fit to the Freundlich equation, and Kd (soil sorption coefficient) and Koc (organic carbon sorption coefficient) values were determined. Sorption and soil system age were directly related to organic matter content in the soil. Sorption of both herbicides increased with age of the soil system and was greatest on the surface soil from the oldest bermudagrass soil system. Herbicide sorption decreased at greater soil depths with lower organic matter. Greater amount of 14C–simazine sorbed to subsurface soil of the oldest turfgrass system compared to 14C–S-metolachlor. Results indicate that as bermudagrass systems age and accumulate higher organic matter levels increased herbicide sorption may decrease the leaching potential and bioavailability of simazine and S-metolachlor. Nomenclature: Simazine; S-metolachlor; bermudagrass; Cynodon dactylon [(L.) Pers.].

Annual Bluegrass (Poa annua) Control in Creeping Bentgrass Putting Greens with Amicarbazone and Paclobutrazol

Abstract Amicarbazone is a photosystem II–inhibiting herbicide recently registered for annual bluegrass control in established turf systems that include creeping bentgrass. However, research to date reveals potential issues with creeping bentgrass tolerance to amicarbazone. Currently, the plant-growth regulator paclobutrazol is widely adopted by turf managers for chemical annual bluegrass suppression in creeping bentgrass putting greens. Field experiments were conducted throughout North Carolina in the spring of 2010 and 2011 to assess treatment regimens that included amicarbazone (49, 65, or 92 g ai ha−1) and paclobutrazol (70, 140, or 280 g ai ha−1) applied alone, as tank-mixtures, or used in tandem, at varying rates and sequential timings for annual bluegrass control in creeping bentgrass putting greens. In general, regimens including both compounds provided greater annual bluegrass control and acceptable turfgrass tolerance compared with stand-alone applications of amicarbazone at 8 and 12 wk after initial treatment (WAIT). When comparing regimens that included amicarbazone at 49 or 65 g ha−1, creeping bentgrass tolerance was greater for the higher application rate applied less frequently. These results indicate amicarbazone usage on creeping bentgrass greens may be beneficially affected with the incorporation of paclobutrazol to treatment regimens because annual bluegrass control with the combination was equal to or greater than stand-alone amicarbazone applications, and creeping bentgrass tolerance was superior 8 and 12 WAIT. Nomenclature: Amicarbazone; paclobutrazol; annual bluegrass; Poa annua L.; creeping bentgrass; Agrostis stolonifera L. Resumen Amicarbazone es un herbicida inhibidor del fotosistema II que fue recientemente registrado para el control de Poa annua en sistemas de céspedes establecidos incluyendo Agrostis stolonifera. Sin embargo, la investigación hasta la fecha revela problemas potenciales con la tolerancia de A. stolonifera a amicarbazone. Actualmente, el regulador de crecimiento paclobutrazol es ampliamente adoptado por especialistas en céspedes para la supresión química de P. annua en putting greens de A. stolonifera. Experimentos de campo fueron realizados en North Carolina en la primavera de 2010 y 2011 para evaluar regímenes con tratamientos que incluyeron amicarbazone (49, 65, ó 92 g ai ha−1) y paclobutrazol (70, 140, ó 280 g ai ha−1), aplicados solos o en mezcla en tanque, o usados en tándem, a dosis variables y en aplicaciones secuenciales para el control de P. annua en putting greens de A. stolonifera. En general, los regímenes que incluyeron ambos compuestos brindaron un mayor control de P. annua y una tolerancia aceptable del césped en comparación con aplicaciones solas de amicarbazone a 8 y 12 semanas después del tratamiento inicial (WAIT). Cuando se compararon regímenes que incluyeron amicarbazone a 49 ó 65 g ha−1, la tolerancia del césped fue mayor cuando las dosis más altas fueron aplicadas en menor frecuencia. Estos resultados indican que el uso de amicarbazone en greens de A. stolonifera podría ser afectado beneficiosamente con la incorporación de paclobutrazol porque el control de P. annua con la combinación fue igual o mayor que las aplicaciones solas de amicarbazone, y la tolerancia del césped fue superior a 8 y 12 WAIT.