Greg K. Breeden

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.

Mesotrione plus Prodiamine for Smooth Crabgrass (Digitaria ischaemum) Control in Established Bermudagrass Turf

Crabgrass species are problematic weeds in bermudagrass turf that can be controlled by PRE herbicide applications. Because of the difficulty in predicting crabgrass emergence and other prevailing management constraints, PRE herbicide applications are not always properly timed. Mesotrione controls crabgrass both PRE and POST; however, relatively short soil-residual activity limits its use as a PRE herbicide. Two experiments were conducted to evaluate smooth crabgrass control with PRE applications of mesotrione plus prodiamine. The first experiment evaluated the influence of application timing on the efficacy of mesotrione-plus-prodiamine combinations. Applications were made every 2 wk from March 15 to May 24. Mesotrione plus prodiamine controlled smooth crabgrass more consistently across all application dates than either mesotrione or prodiamine applied alone. The second experiment evaluated mesotrione along with current PRE and early POST herbicide treatments used for control of crabgrass. When applied at one to two tillers growth stage, mesotrione plus prodiamine controlled smooth crabgrass 99% when rated on August 31. Bermudagrass injury from mesotrione ranged from 9 to 44%, but did not result in any reduction in turf plant density. Mesotrione plus prodiamine is an effective tank mixture when prodiamine alone is not applied in a timely fashion; however, variable and excessive turf injury is a potential impediment to mesotrione use on bermudagrass turf. Nomenclature: Mesotrione, prodiamine, smooth crabgrass, Digitaria ischaemum (Schreb) Schreb. ex Muhl Schreb. DIGIS, bermudagrass, Cynodon dactylon L. CYNDA

Evaluation of Annual Bluegrass Control Programs for Bermudagrass Turf Overseeded with Perennial Ryegrass

Abstract Few herbicides are available that will selectively control annual bluegrass in a polyculture of bermudagrass overseeded with perennial ryegrass. Research was conducted to evaluate multifaceted annual bluegrass control programs in overseeded bermudagrass. Treatments included various combinations of four herbicides: foramsulfuron applied 2 wk prior to overseeding (WPO); ethofumesate and bispyribac-sodium (bispyribac) applied 12 or 12 followed by (fb) 15 wk after overseeding (WAO); and prodiamine applied 15 WAO to provide continued PRE annual bluegrass control. Foramsulfuron at 0.03 kg ha−1 applied 2 WPO controlled annual bluegrass 63% 28 WAO. Foramsulfuron fb ethofumesate or bispyribac applied 12 or 12 fb 15 WAO improved control to 91% or greater. Ethofumesate or bispyribac applied with prodiamine at 1.1 kg ha−1 at 15 WAO did not improve annual bluegrass control compared with ethofumesate or bispyribac treatments alone according to pairwise contrasts. Only bispyribac-containing treatments induced unacceptable perennial ryegrass injury. Bispyribac applied with prodiamine reduced perennial ryegrass cover greater than bispyribac alone according to pairwise contrast. These data indicate that ethofumesate or bispyribac applied sequentially 12 and 15 WPO can effectively control annual bluegrass in bermudagrass turf overseeded with perennial ryegrass. Nomenclature: Bispyribac, ethofumesate, foramsulfuron, prodiamine; annual bluegrass, Poa annua L.; bermudagrass, Cynodon dactylon (L.) Pers., ‘Riviera’; hybrid bermudagrass, Cynodon dacylon (L.) Pers. X C. transvaalensis Burtt-Davy, ‘Tifway’; perennial ryegrass (Lolium perenne L.) LOLPE ‘Palmer IV’

Effect of Reed-Sedge Peat Moss on Hybrid Bermudagrass Injury with Indaziflam and Prodiamine in Sand-Based Root Zones

Abstract PRE herbicides have been reported to injure both the foliage and roots of hybrid bermudagrass turf established in sand culture. Research was conducted to evaluate the influence of reed-sedge peat moss (RSPM) on hybrid bermudagrass injury following PRE herbicide applications to plants established in sand culture. Washed sod plugs were established in mini-rhizotrons constructed with sand root-zones varying in organic carbon content (0.000, 0.003, 0.007, and 0.012 kg kg−1). Herbicide treatments included indaziflam (35 and 52.5 g ai ha−1) and prodiamine (840 g ai ha−1). Significant foliar injury was only observed with indaziflam at 52.5 g ha−1. When applied to plants in sand with no detectable (0.000 kg kg−1) organic carbon, foliar injury measured 61% by 6 wk after treatment. Comparatively, injury with indaziflam at 52.5 g ha−1 was reduced by 40% with applications to plants established in sand with 0.007 kg kg−1 organic carbon. Root length, root length density, and root surface area were greatest in sand-based root zones with ≥ 0.007 kg kg−1 organic carbon regardless of herbicide treatment; however, only indaziflam (52.5 g ha−1) and prodiamine-treated plants exhibited diminished root parameters relative to the nontreated check. Data in the current study illustrate that RSPM can affect above- and belowground injury following PRE herbicide applications to hybrid bermudagrass in sand root-zones. Nomenclature: Indaziflam; prodiamine; hybrid bermudagrass; Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davey. Resumen Los herbicidas PRE han sido reportados como causantes del daño en el follaje y las raíces del césped bermuda híbrido en cultivo en arena. Se realizó una investigación para evaluar la influencia del musgo Sphagnum (RSPM) sobre el daño del césped bermuda híbrido después de aplicaciones de herbicidas PRE a plantas establecidas en cultivo en arena. Fragmentos lavados de estolones enraizados fueron establecidos en mini-rizotrones construidos con zonas de crecimiento radical de arena con un contenido variable de carbono orgánico (0.000, 0.003, 0.007, y 0.012 kg kg−1). Los tratamientos con herbicidas incluyeron (indaziflam 35 y 52.5 g ai ha−1) y prodiamine (840 g ai ha−1). Se observó un daño foliar significativo con indaziflam a 52.5 g ha−1. Cuando se aplicó a plantas en arena con carbono orgánico no detectable (0.000 kg kg−1), el daño foliar fue 61% a 6 semanas después del tratamiento. Comparativamente, el daño con indaziflam a 52.5 g ha−1 fue reducido en 40% con aplicaciones a plantas establecidas en arena con 0.007 kg kg−1 carbono orgánico. Las máximas longitud, longitud-densidad y área superficial de las raíces se observaron en zonas de crecimiento radical de arena con ≥0.007 kg kg−1 carbono orgánico sin importar el tratamiento del herbicida. Sin embargo, solamente plantas tratadas con indaziflam (52.5 g ha−1) y prodiamine exhibieron disminuciones en los parámetros de raíz en relación con el testigo no tratado. Los datos del presente estudio ilustran cómo RSPM puede afectar el daño del tejido aéreo y subterráneo en el césped bermuda híbrido posterior a aplicaciones de herbicidas PRE en las zonas de crecimiento radical en arena.

Yellow nutsedge (Cyperus esculentus) and large crabgrass (Digitaria sanguinalis) response to soil- and foliar-applied mesotrione.

Abstract Mesotrione, a carotenoid biosynthesis inhibitor, is being evaluated for use in turfgrass systems. It was hypothesized that root absorption of soil-applied mesotrione is necessary for effective weed control. Greenhouse studies were conducted to compare the effects of foliar-, soil-, and soil-plus-foliar–applied mesotrione at 0.14 and 0.28 kg ai/ha on yellow nutsedge and large crabgrass. In general, greatest control of yellow nutsedge and large crabgrass was by treatments that included soil application. In addition, mesotrione applied at 0.28 kg/ha generally controlled both yellow nutsedge and large crabgrass more effectively than mesotrione applied at 0.14 kg/ha. Soil- and soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled yellow nutsedge more than foliar-applied mesotrione 56 d after treatment. Soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled large crabgrass more than any other treatment 28 d after treatment. Soil- and soil-plus-foliar–applied mesotrione at both rates reduced large crabgrass foliar dry weight more effectively than did foliar-applied mesotrione. Results indicate that root absorption of mesotrione from soil is beneficial for the effective control of both yellow nutsedge and large crabgrass. For this reason, methods such as granular or high-volume applications, which enhance delivery of mesotrione to soil, would be potentially beneficial for turfgrass weed control. Nomenclature: Mesotrione; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; yellow nutsedge, Cyperus esculentus L. CYPES

Efficacy of Sodium Chloride Applications for Control of Goosegrass (Eleusine Indica) in Seashore Paspalum Turf

Abstract Control of goosegrass is difficult in the pan-Pacific region. No herbicides are currently labeled for selective control of goosegrass in seashore paspalum turf, a species used regularly on golf courses throughout the tropics. Sequential granular applications of sodium chloride (99% sodium chloride, 1% sodium silicoaluminate, 83% 0.5 to 0.25 mm diam) at 488 kg/ha did not effectively (> 70%) control goosegrass in this study. Goosegrass injury following sequential granular applications of sodium chloride, at 488 kg/ha, subsided at 6 wk after initial treatment (WAIT). A single application of MSMA at 2.40 kg/ha plus metribuzin at 0.56 kg/ha provided 96 and 83% control of goosegrass 8 WAIT in 2007 and 2008, respectively. Sequential applications of MSMA plus metribuzin at lower rates yielded similar results. Applications of foramsulfuron did not effectively control (> 70%) goosegrass in this study, suggesting a possible tolerance to this treatment. Applications of MSMA plus metribuzin controlled goosegrass (> 70%), but induced phytotoxic injury to seashore paspalum turf. Additional research is needed to evaluate strategies for POST control of goosegrass in seashore paspalum turf that do not induce phytotoxic turfgrass injury after application. Nomenclature: Metribuzin; MSMA; foramsulfuron; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; seashore paspalum, Paspalum vaginatum Swartz. PASVA

Sodium Chloride Salt Applications Provide Effective Control of Sourgrass (Paspalum conjugatum) in Seashore Paspalum Turf

Abstract Sourgrass is a stoloniferous perennial grassy weed found on golf courses throughout Hawaii. No herbicides are currently labeled for selective control of sourgrass in seashore paspalum turf, a species used regularly on golf courses throughout the tropics. A single granular application of fine salt (99% sodium chloride, 1% sodium silicoaluminate, 83% of particles 0.5 to 0.25 mm in diameter) at a rate of 1,464 kg/ha provided 84 and 23% control of sourgrass 6 wk after initial treatment (WAIT) in 2007 and 2008, respectively. Sequential granular applications of fine salt at 488 kg/ha provided 92 and 96% control of sourgrass in 2007 and 2008, respectively, at 6 WAIT. Granular applications of a coarse salt (100% sodium chloride, 75% of particles 2.0 to 1.0 mm in diameter) provided a lower level of control than fine salt at both the 1,464- and 488-kg/ha rates on three out of four rating dates in 2008; a similar trend was observed in 2007, but no significant differences were observed between these treatments. All salt treatments led to higher soil sodium adsorption ratios (SAR) and electrical conductivity (ECe) than the untreated check; however, levels reported in this study were significantly lower than the threshold SAR and ECe levels that have been associated with reduced seashore paspalum growth. Sequential applications of MSMA at 1.12 kg/ha and MSMA plus metribuzin at 1.12 kg/ha and 0.28 kg/ha, respectively, provided greater than 90% control in 2008, but less than 40% control in 2007. Greater seashore paspalum injury was observed following applications of MSMA and MSMA plus metribuzin than following salt applications. Additional research is needed to evaluate strategies for controlling sourgrass in seashore paspalum turf that do not induce phytotoxic injury after application. Nomenclature: Metribuzin; MSMA; sourgrass, Paspalum conjugatum Berg. PASCO; seashore paspalum, Paspalum vaginatum Swartz. PASVA.

Common Bermudagrass Seedhead Suppression and Growth Regulation with Fenoxaprop

Abstract Options for suppressing bermudagrass seedheads in managed turfgrass systems are limited. Experiments were conducted in 2009 and 2010 evaluating the use of fenoxaprop (25, 50, 75, and 100 g ha−1) for ‘Riviera’ bermudagrass seedhead suppression and growth regulation compared to imazapic (52 g ha−1), trinexapac-ethyl (91 g ha−1) and mefluidide (561 g ha−1). In field experiments, seedhead suppression ranged from 77 to 100% for fenoxaprop and imazapic at 35 d after treatment (DAT). Comparatively, seedhead suppression was < 25% for either trinexapac-ethyl or mefluidide at 35 DAT. Seedhead suppression was > 90% from 7 to 35 DAT for fenoxaprop applied at ≥ 50 g ha−1. Injury, determined visually, from fenoxaprop and imazapic in both the field and greenhouse measured < 25% on all rating dates, with no significant injury present after 21 DAT. In greenhouse experiments, fenoxaprop and trinexapac-ethyl showed similar reductions of bermudagrass growth; no differences in aboveground biomass were detected between these treatments at 42 DAT. Results of the current study illustrate that fenoxaprop and imazapic can be applied for bermudagrass seedhead suppression and growth regulation if moderate (< 25%) injury can be tolerated up to 21 DAT. Additional research is needed to evaluate the use of fenoxaprop and imazapic for seedhead suppression on other common and hybrid bermudagrasses. Nomenclature: Fenoxaprop; imazapic; mefluidide; trinexapac-ethyl; bermudagrass, Cynodon dactylon (L.) Pers. ‘Riviera’; hybrid bermudagrass C. dactylon × C. transvaalensis Burtt Davy.

Control of Summer Annual Grasses during Seeded Zoysiagrass Establishment with Various Timings and Rates of Fluazifop, Triclopyr, and Fluazifop plus Triclopyr

Abstract Summer annual grasses such as goosegrass and smooth crabgrass can hinder seeded zoysiagrass establishment. The herbicide fluazifop controls various grassy weed species but can injure mature and seedling zoysiagrass. Research has indicated that fluazifop applications can be safened on mature zoysiagrass cultivars with the addition of triclopyr. Based on these observations, research was conducted to evaluate weed control and tolerance of seeded ‘Zenith’ zoysiagrass to fluazifop (0.11 or 0.21 kg ai ha−1), triclopyr (1.12 kg ae ha−1), or fluazifop plus triclopyr (0.11 or 0.21 kg ha−1 plus 1.12 kg ha−1) applied at seeding, 14, or 28 d after emergence (DAE). All herbicide treatments applied at seeding did not hinder zoysiagrass germination but did not reduce goosegrass populations. Fluazifop alone (0.11 and 0.21 kg ha−1) applied at 14 and 28 DAE injured zoysiagrass seedlings but was reduced with the addition of triclopyr. At the end of the growing season, the greatest zoysiagrass cover was achieved by applications of fluazifop alone (0.11 kg ha−1) applied at 14 DAE or fluazifop (0.11 or 0.21 kg ha−1) plus triclopyr applied at 14 or 28 DAE. Fluazifop (0.11 or 0.21 kg ha−1) applied alone or tank-mixed with triclopyr controlled goosegrass > 70% when applied 14 and 28 DAE. Based on these data, applications of fluazifop tank-mixed with triclopyr can successfully control goosegrass without injuring Zenith zoysiagrass seedlings. Nomenclature: Fluazifop-P, (R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid; siduron, N-(2-methylcyclohexyl)-N9-phenylurea; triclopyr, [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid; goosegrass, Eleusine indica (L.) Gaertn., smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl.; zoysiagrass, Zoysia japonica Steud. ‘Zenith’.