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Ornamental plant and weed response to oxyfluorfen + prodiamine herbicide was evaluated in Connecticut and Tennessee, USA, in 2017 and 2018. Preemergence application of oxyfluorfen + prodiamine was made at 0 lb/acre, 2 + 0.75 lb/acre, 4 + 1.5 lb/acre, and 8 + 3 lb/acre to container-grown ornamental plants on an outdoor gravel pad and weeds in greenhouse experiments. Ornamental plants were treated first within a week after transplanting and again 6 weeks after the first treatment. Asiatic jasmine ( Trachelospermum asiaticum ), candlestick plant ( Senna alata ), and English ivy ( Hedera helix ) in Tennessee, USA; and ‘Blue Flag’ iris ( Iris sp.), ‘Firecracker’ gladiolus ( Gladiolus sp.), and ‘Green Carpet’ Japanese pachysandra ( Pachysandra terminalis ) in Connecticut, USA, were not injured with oxyfluorfen + prodiamine regardless of rate applied. Lily-of-the-Nile ( Agapanthus africanus ) in Tennessee, USA, and ‘Bowles’ periwinkle ( Vinca minor ) in Connecticut, USA, showed minor but commercially acceptable growth reduction with oxyfluorfen + prodiamine up to 4 + 1.5 lb/acre. Shasta daisy ( Leucanthemum × superbum ) in Connecticut, USA, was the most sensitive ornamental plant. After the first application, average necrotic injury to Shasta daisy varied from 24% with 2 + 0.75 lb/acre to 31% with 8 + 3 lb/acre of oxyfluorfen + prodiamine. After the second application, necrotic injury was ≤ 5% with all oxyfluorfen + prodiamine rates tested and was commercially acceptable (≤ 20%). Oxyfluorfen + prodiamine reduced densities of creeping woodsorrel ( Oxalis corniculata ), hairy bittercress ( Cardamine hirsuta ), giant foxtail ( Setaria faberi ), and large crabgrass ( Digitaria sanguinalis ) ≥ 80% by 4 weeks after treatment. The fresh weed biomass 6 weeks after treatment indicated an 88% to 99% reduction compared with the untreated control.

Waterhemp (Amaranthus tuberculatus) is an economically important broadleaf weed that threatens corn and soybean production across the United States. A waterhemp biotype (CT_Res [resistant biotype from Connecticut]) surviving multiple glyphosate applications was identified from a corn field in Connecticut (CT). Greenhouse and laboratory studies were conducted to (1) confirm glyphosate resistance in CT_Res waterhemp biotype and (2) investigate if the glyphosate resistance in CT_Res biotype is due to target‐site‐based mechanism. Dose‐response studies indicated that CT_Res biotype was 5.8‐fold more resistant to glyphosate compared to a known susceptible biotype (NE_Sus) from Nebraska. No point mutation was detected at Pro102 or Thr106 positions in the EPSPS gene of the CT_Res biotype. The quantitative polymerase chain reaction assays revealed that one of the three CT_Res waterhemp plants had 3.5‐fold higher EPSPS gene copy number (relative to the housekeeping CPS gene), whereas the other two plants did not reveal EPSPS gene amplification. Obviously, the EPSPS gene amplification partially explains glyphosate resistance in newly identified glyphosate‐resistant waterhemp biotype from CT, indicating that alternative mechanisms might exist. This research reports the first case of glyphosate resistance and EPSPS gene amplification in waterhemp from Connecticut and highlights the need for adoption of diversified weed control strategies to prevent its further spread. Core Ideas A suspected waterhemp biotype from Connecticut was characterized for glyphosate resistance and target‐site based mechanism. Connecticut waterhemp biotype exhibited 5.8‐fold resistance to glyphosate compared to a susceptible biotype from Nebraska. Sequence analysis of the EPSPS gene revealed no mutation at Pro102 or Thr106 positions in Connecticut waterhemp biotype. One of the three glyphosate‐resistant waterhemp plants from Connecticut had 3.5‐fold higher EPSPS gene copy number. Plain Language Summary Waterhemp is one of the most troublesome weed species in the US Midwest. In recent years, waterhemp biotypes are also identified in northeastern United States, including Connecticut and New York. This research was aimed to confirm the presence of glyphosate resistance in a waterhemp biotype collected from a corn field in Connecticut and investigate if the glyphosate resistance was due to target‐site‐based mechanism. Greenhouse studies concluded that waterhemp biotype from Connecticut was 5.8 times more resistant to glyphosate when compared with a known glyphosate‐susceptible biotype from Nebraska. Furthermore, one out of three glyphosate‐resistant waterhemp plants showed 3.5 times higher copies of target gene (EPSPS). Altogether, these results confirm the first report of glyphosate resistance in recently identified waterhemp biotype from Connecticut. Growers need to be vigilant and should adopt diversified weed control strategies to prevent its further spread.

Glyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) is widespread in the Central Great Plains. Introduction of newly developed dicamba/glufosinate/glyphosate (DGG)‐resistant soybean varieties allows postemergence (POST) applications of dicamba and glufosinate for in‐season control of GR Palmer amaranth. Limited information exists on the effectiveness of glufosinate applied late‐POST for tall (70–90 cm) GR Palmer amaranth control in DGG‐resistant soybean. The objectives of this study were to (1) determine the effectiveness of late‐POST glufosinate‐based programs for GR Palmer amaranth control, and (2) determine the impact of those programs on soybeans grain yields. Ten glufosinate‐based programs were tested in a field study at Kansas State University Agricultural Research Center near Hays, Kansas. Results indicated that single (655 or 737 g ha−1) and all sequential (594 followed by [fb] 594, 655 fb 594, and 737 fb 594 g ha−1) applications (7‐days apart) of glufosinate provided 87%–93% control of GR Palmer amaranth 28 days after last POST (DALPOST). Palmer amaranth control with single late‐POST application of glufosinate (594 g ha−1) or glufosinate plus S‐metolachlor did not exceed 84% at 28 DALPOST. Majority of the evaluated programs reduced shoot dry weights of GR Palmer amaranth by 83%–91%. The least control (11%) and shoot dry weight reduction (33%) of GR Palmer amaranth were observed with glyphosate fb glyphosate. Glufosinate‐based programs resulted in soybean grain yield of 626–701 kg ha−1. These results conclude that glufosinate applied late‐POST may provide effective control of tall GR Palmer amaranth in DGG‐resistant soybeans. Core Ideas Late‐POST glufosinate‐based herbicide programs were evaluated in dicamba/glufosinate/glyphosate (DGG)‐resistant soybeans. Single (655 or 737 g ha−1) and all sequential late‐POST glufosinate programs provided 87%–93% control of GR Palmer amaranth. The majority of glufosinate‐based programs reduced shoot dry weights of GR Palmer amaranth by 83%–91%. Late‐POST glufosinate programs had 56%–61% higher soybean yield compared to glyphosate followed by glyphosate.

Asiatic dayflower (Commelina communis L.) is becoming increasingly invasive in Christmas tree plantations in the U.S. Northeast. Response of C. communis to preemergence or postemergence herbicides was evaluated in separate field and greenhouse experiments. The preemergence herbicides consisted of two application rates of flumioxazin (215 and 429 g ai ha–1), hexazinone plus sulfometuron-methyl (316 and 527 g ai ha–1), indaziflam (41 and 82 g ai ha–1), and S-metolachlor (2,136 and 4,272 g ai ha–1). The postemergence herbicides were: bentazon at 1,121 g ai ha–1, clopyralid at 280 g ae ha–1, mesotrione at 526 g ai ha–1, topramezone at 294 g ai ha–1, and triclopyr at 842 g ae ha–1. At 16 wk after treatment, higher rates of flumioxazin (429 g ha–1), hexazinone plus sulfometuron-methyl (527 g ha–1), indaziflam (82 g ha–1), and S-metolachlor (4,272 ha–1) provided 80% to 92% control and reduced C. communis plant density by 84% to 93% compared with the nontreated control. The lower rates of flumioxazin (215 g ha–1), hexazinone plus sulfometuron-methyl (316 g ha–1), and S-metolachlor (2,136 ha–1) gave 65% to 72% control and reduced C. communis plant density by 27% to 75% compared with the nontreated control. The postemergence application of mesotrione at 526 g ha–1, topramezone at 294 g ha–1, and triclopyr at 842 g ha–1 resulted in 76% to 90% control and reduction in dry biomass of 10- to 12-leaf C. communis at 28 d after treatment. Bentazon at 1,121 g ha–1 and clopyralid at 280 g ha–1 applied postemergence were ineffective with <10% control and reduction in C. communis dry biomass. This study showed that C. communis can be managed effectively with currently registered preemergence and postemergence herbicides in Christmas trees.

PRE herbicides are the backbone of a successful weed management program in Christmas tree production. In a 2-yr field study, weed control efficacy and tolerance of newly transplanted Canaan fir to different PRE treatments were evaluated. Herbicide treatments consisted of two rates of each of atrazine plus mesotrione plus S-metolachlor at 561 + 150 + 1,504 and 1,122 + 300 + 3,008 g ai ha–1, flumioxazin at 214 and 429 g ai ha–1, hexazinone plus sulfometuron methyl at 289 + 27 and 480 + 46 g ai ha–1, indaziflam at 20 and 41 g ai ha–1, simazine plus oryzalin at 3,366 + 1,683 and 3,366 + 3,366 g ai ha–1, and a nontreated control. Averaged over 2 yr, all PRE treatments controlled giant foxtail, large crabgrass, and redroot pigweed at least 80% throughout the summer. Only the high rates of atrazine plus mesotrione plus S-metolachlor maintained >80% season-long control of yellow foxtail. Horseweed was controlled >85% with flumioxazin at both rates and at high rates of atrazine plus mesotrione plus S-metolachlor, hexazinone plus sulfometuron methyl, and indaziflam. The season-long PRE control of both red sorrel and wild carrot was maintained ≥80% with atrazine plus mesotrione plus S-metolachlor and hexazinone plus sulfometuron methyl regardless of application rate. By 16 wk after treatment, within-row densities of weeds evaluated in this study were reduced >75% in plots treated with atrazine plus mesotrione plus S-metolachlor at both application rates or hexazinone plus sulfometuron methyl at 480 + 46 g ai ha–1. Within-row weed densities in the nontreated control plots were 50, 32, 36, 25, 27, 31, and 19 plants m–2 for large crabgrass, giant foxtail, horseweed, redroot pigweed, red sorrel, wild carrot, and yellow foxtail, respectively. No discernible injury was observed in Canaan fir with any PRE treatment in both study years. Nomenclature: Atrazine; flumioxazin; hexazinone; indaziflam; mesotrione; oryzalin; simazine; S-metolachlor; sulfometuron methyl; giant foxtail, Setaria faberi Herrm.; horseweed, Conyza canadensis (L.) Cronq.; large crabgrass, Digitaria sanguinalis (L.) Scop.; redroot pigweed, Amaranthus retroflexus (L.); red sorrel, Rumex acetocella (L.); wild carrot, Daucus carota (L.); yellow foxtail, Setaria pumila (Poir.) Roem. & Schult.; Canaan fir, Abies balsamea var. phanerolepis

Mugwort (Artemisia vulgaris L.) is becoming increasingly problematic in cool-season pastures and grasslands. A 3-yr field experiment evaluated different rates of nitrogen and herbicides for A. vulgaris management in a permanent grassland. The main plot had three nitrogen rates, 0, 62, and 124 kg N ha–1; the subplot had three herbicides, aminopyralid, clopyralid, and glyphosate; and the sub-subplot had three herbicide rates, aminopyralid (61, 122, and 244 g ae ha–1), clopyralid (140, 280, and 560 g ae ha–1), and glyphosate (552, 1,104, and 2,208 g ae ha–1). Results revealed that nitrogen had no effect on A. vulgaris control, rhizome biomass, and stem density. However, cool-season grass biomass was the highest (7,126 kg ha–1) in the plots that received 124 kg N ha–1 and 244 g ae ha–1 of aminopyralid. Only glyphosate caused grass injury, which varied from 65% to 100% depending upon application rate. By 9 mo after initial herbicide treatment (MAIT), A. vulgaris was controlled 60% to 98% with aminopyralid at ≥61 g ae ha–1 or glyphosate at ≥552 g ae ha–1. By 21 MAIT, aminopyralid at ≥122 g ae ha–1 or glyphosate at ≥1,104 g ae ha–1 resulted in >95% reduction in A. vulgaris stem density and rhizome biomass and provided ≥98% visual control. By 33 MAIT, complete control of A. vulgaris was confirmed in plots treated with aminopyralid at ≥122 g ae ha–1 or glyphosate at ≥1,104 g ae ha–1. Clopyralid was not effective; A. vulgaris control was <40% even after three annual applications at 560 g ae ha–1. Results indicate that integration of nitrogen fertilization with aminopyralid did not improve A. vulgaris control, but was advantageous in enhancing cool-season grass productivity.

Cotton (Gossypium hirsutum L.) producers in Alabama are faced with a rapidly expanding problem that decreases yields and increases production costs: herbicide-resistant weeds. Producers increasingly rely on integrated weed management strategies that raise production costs. This analysis evaluated how tillage, cover crops, and herbicide regime affected net returns above variable treatment costs (net returns) for cotton production in Alabama from 2009 to 2011 under pressure from Palmer amaranth (Amaranthus palmeri S. Wats.). Annual net returns were compared for two tillage treatments (inversion and noninversion tillage), three cover crops (crimson clover [Trifolium incarnatum L.], cereal rye [Secale cereal L.], and winter fallow), and three herbicide regimes (PRE, POST, and PRE+POST). Results indicate that under heavy Palmer amaranth population densities one year of inversion tillage followed by two years of noninversion tillage, along with a POST or PRE+POST herbicide application had the highest net returns in the first year; however, the economic benefit of inversion tillage, across all herbicide treatments, was nonexistent in 2010 and 2011. Cotton producers with Palmer amaranth infestations would likely benefit from cultural controls, in conjunction with herbicide applications, as part of their weed management system to increase net returns.

A Palmer amaranth biotype (CT-Res) with resistance to glyphosate was recently confirmed in a pumpkin field in Connecticut. However, the underlying mechanisms conferring glyphosate resistance in this biotype is not known. The main objectives of this research were 1) to determine the effect of plant height (10, 20, and 30 cm) on glyphosate resistance levels in CT-Res Palmer amaranth biotype, and 2) to investigate whether the target site–based mechanisms confer glyphosate resistance. To achieve these objectives, progeny seeds of the CT-Res biotype after two generations of recurrent selection with glyphosate (6,720 g ae ha–1) were used. Similarly, known glyphosate-susceptible Palmer amaranth biotypes from Kansas (KS-Sus) and Alabama (AL-Sus) were included. Results from greenhouse dose-response studies revealed that CT-Res Palmer amaranth biotype had 69-, 64-, and 54-fold resistance to glyphosate as compared with the KS-Sus biotype when treated at heights of 10, 20, and 30 cm, respectively. Sequence analysis of the EPSPS gene revealed no point mutations at the Pro106 and Thr102 residues in the CT-Res Palmer amaranth biotype. Quantitative polymerase chain reaction analysis revealed that the CT-Res biotype had 33 to 111 relative copies of the EPSPS gene compared with the AL-Sus biotype. All these results suggest that the EPSPS gene amplification endows a high level of glyphosate resistance in the GR Palmer amaranth biotype from Connecticut. Because of the lack of control with glyphosate, growers should adopt the use of effective alternative preemergence and postemergence herbicides in conjunction with other cultural and mechanical tactics to mitigate the further spread of GR Palmer amaranth in Connecticut. Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Watson; pumpkin (Cucurbita pepo L.)

Because of the increasing number of glyphosate-resistant weeds, alternate herbicide-resistant crops and herbicides with different modes of action are required to protect crop yield. Glufosinate is a broad-spectrum POST herbicide for weed control in glufosinate-resistant crops, including soybean. The objective of this study was to compare herbicide programs with glufosinate applied singly at late-POST (LPOST) or sequentially at early POST (EPOST) followed by (fb) LPOST applications and PRE herbicides fb EPOST/LPOST glufosinate alone or tank-mixed with acetochlor, pyroxasulfone, or S-metolachlor in glufosinate-resistant soybean. A field experiment was conducted at the South Central Agriculture Laboratory in Clay Center, NE, in 2012 and 2013. Glufosinate applied in a single LPOST or sequential EPOST fb LPOST application controlled common lambsquarters, common waterhemp, eastern black nightshade, green foxtail, large crabgrass, and velvetleaf ≤ 82% and resulted in a weed density of 6 to 10 plants m−2 by the end of the season. Flumioxazin-, saflufenacil-, or sulfentrazone-based premixes provided 84 to 99% control of broadleaf and grass weeds tested in this study at 15 d after PRE application and a subsequent LPOST application of glufosinate alone controlled broadleaf and grass weeds 69 to 93% at harvest, depending on the herbicide program and weed species being investigated. The PRE application of sulfentrazone plus metribuzin fb EPOST glufosinate tank-mixed with acetochlor, pyroxasulfone, or S-metolachlor controlled the tested broadleaf and grass weeds ≥ 90%, reduced density to ≤ 2 plants m−2, and reduced weed biomass to ≤ 10 g m−2 and produced soybean yields of ≥ 4,450 and 3,040 kg ha−1 in 2012 and 2013, respectively. Soybean injury was 0 to 20% from PRE or POST herbicides, or both and was inconsistent, but transient, during the 2-yr study, and it did not affect soybean yield. Sulfentrazone plus metribuzin applied PRE fb glufosinate EPOST tank-mixed with acetochlor, pyroxasulfone, or S-metolachlor provided the highest level of weed control throughout the growing season and increased soybean yield compared with a single LPOST or a sequential EPOST fb LPOST glufosinate application. Additionally, these herbicide programs provide four distinct mechanisms of action that constitute an effective weed-resistance management strategy in glufosinate-resistant soybean. Nomenclature: Acetochlor; flumioxazin; glufosinate; metribuzin; pyroxasulfone; saflufenacil; S-metolachlor; sulfentrazone; common lambsquarters, Chenopodium album L.; common waterhemp, Amaranthus rudis Sauer; eastern black nightshade, Solanum ptychanthum Dunal; green foxtail, Setaria viridis (L.) Beauv.; large crabgrass, Digitaria sanguinalis (L.) Scop.; velvetleaf, Abutilon theophrasti Medik; soybean, Glycine max (L.) Merr. Debido al creciente número de malezas resistentes a glyphosate, es necesario alternar cultivos resistente a herbicidas con diferentes modos de acción para proteger los rendimientos de los cultivos. Glufosinate es un herbicida POST de amplio espectro para el control de malezas en cultivos resistentes a glufosinate, incluyendo soja. El objetivo de este estudio fue comparar programas de herbicidas con glufosinate aplicado solo en POST-tarde (LPOST), o secuencialmente en POST-temprano (EPOST) seguido de (fb) aplicaciones LPOST, y herbicidas PRE fb glufosinate solo en EPOST/LPOST, o mezclas en tanque con acetochlor, pyroxasulfone, o S-metolachlor, en soja resistente a glufosinate. Se realizó un experimento de campo en el Laboratorio de Agricultura del Centro Sur, en Clay Center, Nebraska, en 2012 y 2013. Glufosinate aplicado solo LPOST o en secuencia EPOST fb LPOST controló Chenopodium album, Amaranthus rudis, Solanum ptychanthum, Setaria viridis, Digitaria sanguinalis, y Abutilon theophrasti ≤ 82% y resultaron en una densidad de malezas de 6 a 10 plantas m−2 al final de la temporada. Premezclas basadas en flumioxazin, saflufenacil, o sulfentrazone brindaron 84 a 99% de control de malezas de hoja ancha y gramíneas evaluadas en este estudio a 15 d después de la aplicación; PRE fb glufosinate solo (EPOST/LPOST) controlaron malezas de hoja ancha y gramíneas 69 a 93% al momento de la cosecha, dependiendo del programa de herbicidas y las especies de malezas investigadas. La aplicación PRE de sulfentrazone más metribuzin fb EPOST con glufosinate mezclado en tanque con acetochlor, pyroxasulfone, o S-metolachlor controló las especies de malezas de hoja ancha y gramíneas evaluadas ≥ 90%, redujo la densidad ≤ 2 plantas m−2, redujo la biomasa de malezas ≤ 10 g m−2, y produjo rendimientos de soja ≥ 4,450 y 3,040 kg ha−1, en 2012 y 2013, respectivamente. El daño en la soja fue 0 a 20% en los tratamientos PRE, POST, o ambos, y fue inconsistente pero fue transitorio, durante los 2 años del estudio, y no afectó el rendimiento de la soja. Sulfentrazone más metribuzin aplicados PRE fb glufosinate EPOST mezclado en tanque con acetochlor, pyroxasulfone, o S-metolachlor brindó el mayor nivel de control de malezas a lo largo de la temporada de crecimiento e incrementó el rendimiento de la soja al compararse con una aplicación de glufosinate LPOST o aplicaciones secuenciales EPOST fb EPOST. Adicionalmente, estos programas de herbicidas permitieron el uso de cuatro mecanismos de acción distintos lo que constituye una estrategia efectiva para el manejo de resistencia en soja resistente a glufosinate.

A three year field experiment was conducted to evaluate the role of soil-inversion, cover crops and herbicide regimes for Palmer amaranth between-row (BR) and within-row (WR) management in glufosinate-resistant cotton. The main plots were two soil-inversion treatments: fall inversion tillage (IT) and non-inversion tillage (NIT). The subplots were three cover crop treatments: crimson clover, cereal rye and winter fallow; and sub subplots were four herbicide regimes: preemergence (PRE) alone, postemergence (POST) alone, PRE + POST and a no herbicide check (None). The PRE herbicide regime consisted of a single application of pendimethalin at 0.84 kg ae ha−1 plus fomesafen at 0.28 kg ai ha−1. The POST herbicide regime consisted of a single application of glufosinate at 0.60 kg ai ha−1 plus S-metolachlor at 0.54 kg ai ha−1 and the PRE + POST regime combined the prior two components. At 2 weeks after planting (WAP) cotton, Palmer amaranth densities, both BR and WR, were reduced ≥90% following all cover crop treatments in the IT. In the NIT, crimson clover reduced Palmer amaranth densities >65% and 50% compared to winter fallow and cereal rye covers, respectively. At 6 WAP, the PRE and PRE + POST herbicide regimes in both IT and NIT reduced BR and WR Palmer amaranth densities >96% over the three years. Additionally, the BR density was reduced ≥59% in no-herbicide (None) following either cereal rye or crimson clover when compared to no-herbicide in the winter fallow. In IT, PRE, POST and PRE + POST herbicide regimes controlled Palmer amaranth >95% 6 WAP. In NIT, Palmer amaranth was controlled ≥79% in PRE and ≥95% in PRE + POST herbicide regimes over three years. POST herbicide regime following NIT was not very consistent. Averaged across three years, Palmer amaranth controlled ≥94% in PRE and PRE + POST herbicide regimes regardless of cover crop. Herbicide regime effect on cotton yield was highly significant; the maximum cotton yield was produced by the PRE + POST herbicide regime. Averaged over three years, the PRE, POST and PRE + POST cotton yields were about three times higher than no herbicide regime. In a conservation tillage production system, a PRE + glufosinate POST herbicide based regime coupled with a cereal rye cover crop may effectively control Palmer amaranth and maximize cotton yields.