Debalin Sarangi

Confirmation and control of glyphosate-resistant common waterhemp (Amaranthus rudis) in Nebraska.

Abstract Glyphosate-resistant common waterhemp is a difficult-to-control annual broadleaf weed that has become a serious management challenge for growers in Nebraska and other states in the United States. The objectives of this study were to confirm glyphosate-resistant common waterhemp in Nebraska by quantifying level of resistance in a dose-response study, and to determine the sensitivity and efficacy of POST soybean herbicides for controlling suspected glyphosate-resistant common waterhemp biotypes. Seeds of suspected glyphosate-resistant common waterhemp biotypes were collected from seven eastern Nebraska counties. Greenhouse dose-response experiments were conducted to evaluate the response of common waterhemp biotypes to nine rates of glyphosate (0 to 16×). Common waterhemp biotypes were 3- to 39-fold resistant to glyphosate depending on the biotype being investigated and the susceptible biotype used for comparison. Results of the POST soybean herbicides efficacy experiment suggested that glyphosate-resistant biotypes, except a biotype from Pawnee County, had reduced sensitivity to acetolactate synthase (ALS)–inhibiting herbicides (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, and thifensulfuron-methyl). Glufosinate and protoporphyrinogen oxidase (PPO)–inhibiting herbicides (acifluorfen, fluthiacet-methyl, fomesafen, and lactofen) provided ≥ 80% control of glyphosate-resistant common waterhemp at 21 d after treatment (DAT). This study confirmed the first occurrence of glyphosate-resistant common waterhemp in Nebraska, and also revealed reduced sensitivity to ALS-inhibiting herbicides in most of the biotypes tested in this study. Nomenclature: Acifluorfen; chlorimuron-ethyl; fluthiacet-methyl; fomesafen; glufosinate; glyphosate; imazamox; imazaquin; imazethapyr; lactofen; thifensulfuron-methyl; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr. Resumen Amaranthus rudis resistente a glyphosate es una maleza anual de hoja ancha difícil de controlar y que se ha convertido en un reto serio de manejo para productores en Nebraska y otros estados en los Estados Unidos. Los objetivos de este estudio fueron confirmar la resistencia a glyphosate de A. rudis en Nebraska, cuantificando el nivel de resistencia mediante estudios de respuesta a dosis, y determinar la sensibilidad y la eficacia de herbicidas POST para soja para el control de biotipos de A. rudis que se sospecha son resistentes a glyphosate. En siete condados del este de Nebraska, se colectaron semillas de biotipos de A. rudis que se sospechaba eran resistentes a glyphosate. Se realizaron experimentos de respuesta a dosis en invernadero, para evaluar la respuesta de biotipos de A. rudis a nueve dosis de glyphosate (0 a 16X). Biotipos de A. rudis fueron de 3 a 39 veces más resistentes a glyphosate, dependiendo del biotipo investigado y del biotipo susceptible usados en la comparación. Los resultados del experimento sobre la eficacia de herbicidas POST para soja sugirieron que los biotipos resistentes a glyphosate, con la excepción del biotipo proveniente del condado Pawnee, tuvieron una sensibilidad reducida a los herbicidas inhibidores de acetolactate synthase (ALS) (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, y thifensulfuron-methyl). Glufosinate y los herbicidas inhibidores de protoporphyrinogen oxidase (PPO) (acifluorfen, fluthiacet-methyl, fomesafen, y lactofen) brindaron ≥ 80% control de A. rudis resistente a glyphosate a 21 d después del tratamiento (DAT). Este estudio confirmó el primer caso de A. rudis resistente a glyphosate en Nebraska, y también reveló la sensibilidad reducida a herbicidas inhibidores de ALS en la mayoría de los biotipos evaluados en este estudio.

Effect of Water Stress on the Growth and Fecundity of Common Waterhemp (Amaranthus rudis)

Abstract Common waterhemp is one of the most commonly encountered and troublesome weeds in the midwestern United States. It is well known that water stress adversely affects crop growth and yield; however, the effects of water stress on weed growth and seed production are poorly understood. The objective of this study was to determine the effects of degree and duration of water stress on growth, development, and fecundity of two common waterhemp biotypes in greenhouse experiments conducted at the University of Nebraska–Lincoln. No difference was observed in growth, development, and seed production between two biotypes in response to degree and duration of water stress; therefore, data were combined. The degree of water stress study included five treatments, where the amount of water applied to each pot at 2-d interval was equivalent to 100, 75, 50, 25, and 12.5% of pot (soil) water content. The highest plant height (163 cm), number of leaves (231 plant−1), and growth index (4.4 × 105 cm3) were recorded at 100% of pot water content (no water stress). Similarly, aboveground biomass, total leaf area, and seed production reached their maximum at 100% of pot water content treatment, whereas they were reduced as degree of water stress increased. The study of water stress duration included five treatments, where amount of water applied to each pot at 2-, 4-, 6-, 8-, and 10-d intervals was equivalent to 100% of pot water content. The highest plant height (150 cm), number of leaves (210 plant−1), and growth index (3.8 × 105 cm3) were observed at 2-d interval of water stress, whereas seed production was similar at 2-d (36,549 seeds plant−1) and 4-d (34,176 seeds plant−1) intervals. This study shows that common waterhemp has capacity to survive and reproduce even under a higher degree and duration of water stress. Nomenclature: Common waterhemp; Amaranthus rudis Sauer.

Pollen-mediated gene flow from glyphosate-resistant common waterhemp ( Amaranthus rudis Sauer): consequences for the dispersal of resistance genes

Gene flow is an important component in evolutionary biology; however, the role of gene flow in dispersal of herbicide-resistant alleles among weed populations is poorly understood. Field experiments were conducted at the University of Nebraska-Lincoln to quantify pollen-mediated gene flow (PMGF) from glyphosate-resistant (GR) to -susceptible (GS) common waterhemp using a concentric donor-receptor design. More than 130,000 common waterhemp plants were screened and 26,199 plants were confirmed resistant to glyphosate. Frequency of gene flow from all distances, directions, and years was estimated with a double exponential decay model using Generalized Nonlinear Model (package gnm) in R. PMGF declined by 50% at <3 m distance from the pollen source, whereas 90% reduction was found at 88 m (maximum) depending on the direction of the pollen-receptor blocks. Amplification of the target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), was identified as the mechanism of glyphosate resistance in parent biotype. The EPSPS gene amplification was heritable in common waterhemp and can be transferred via PMGF, and also correlated with glyphosate resistance in pseudo-F2 progeny. This is the first report of PMGF in GR common waterhemp and the results are critical in explaining the rapid dispersal of GR common waterhemp in Midwestern United States.

Comparison of Herbicide Programs for Season-Long Control of Glyphosate-Resistant Common Waterhemp (Amaranthus rudis) in Soybean

The evolution of glyphosate and acetolactate synthase (ALS) inhibitor-resistant common waterhemp in the Midwestern United States has reduced the number of effective POST herbicide options for management of this problem weed in glyphosate-resistant soybean. Moreover, common waterhemp emerges throughout the crop growing season, justifying the need to evaluate herbicide programs that provide season-long control. The objectives of this study were to compare POST-only and PRE followed by (fb) POST herbicide programs for control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Field experiments were conducted in 2013 and 2014 in Dodge County, NE, in a field infested with glyphosate-resistant common waterhemp. Programs containing PRE herbicides resulted in ≥83% control of common waterhemp and densities of ≤35 plantsm−2 at 21 d after PRE (DAPRE). Post-only herbicide programs resulted in <70% control and densities of 107 to 215 plants m−2 at 14 d after early-POST (DAEPOST) treatment. PRE fb POST herbicide programs, including saflufenacil plus imazethapyr plus dimethenamid-P, sulfentrazone plus cloransulam, or S-metolachlor plus metribuzin, fb fomesafen plus glyphosate; S-metolachlor plus fomesafen fb acifluorfen plus glyphosate resulted in >90% control of glyphosate-resistant common waterhemp throughout the growing season, reduced density to ≤7plantsm−2, ≥92% biomass reduction, and soybean yield >2,200kg ha−1. Averaged across herbicide programs, common waterhemp control was 84%, and density was 15 plants m−2 with PRE fb POST herbicide programs compared with 42% control, and density of 101 plants m−2 with POST-only herbicide programs at harvest. Results of this study indicated that PRE fb POST herbicide programs with effective modes of action exist for season-long control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Nomenclature: Acetochlor; acifluorfen; chlorimuron-ethyl; cloransulam-methyl; dimethenamid-P; flumioxazin; fomesafen; glyphosate; imazethapyr; lactofen; saflufenacil; S-metolachlor; sulfentrazone; thifensulfuron-methyl; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr. La evolución de Amaranthus rudis resistente a glyphosate y a inhibidores de acetolactate synthase en el medio oeste de los Estados Unidos ha reducido el número de opciones efectivas de herbicidas POST para el manejo de esta problemática maleza en soja resistente a glyphosate. Además, A. rudis emerge a lo largo de la temporada de crecimiento del cultivo, lo que justifica la necesidad de evaluar programas de herbicidas que brinden control durante toda la temporada. Los objetivos de este estudio fueron comparar programas con sólo herbicidas POST y con herbicidas PRE seguidos por (fb) herbicidas POST para el control de A. rudis resistente a glyphosate en soja resistente a glyphosate. Se realizaron experimentos de campo en 2013 y 2014 en el condado Dodge, en Nebraska, en campos infestados con A. rudis resistente a glyphosate. Los programas que contenían herbicidas PRE resultaron en ≥83% de control de A. rudis y en densidades de ≤35 plantas m−2 a 21 d después de PRE (DAPRE). Programas con sólo herbicidas POST resultaron en <70% de control y densidades de 107 a 215 plantas m−2 a 14d después del tratamiento POST temprano (DAEPOST). Programas de herbicidas PRE fb POST, incluyendo saflufenacil más imazethapyr más dimethenamid-P, sulfentrazone más cloransulam, o S-metolachlor más metribuzin, fb fomesafen más glyphosate; S-metolachlor más fomesafen fb acifluorfen más glyphosate resultaron en >90% de control de A. rudis resistente a glyphosate a lo largo de la temporada, densidad reducida a ≤7 plantas m−2, reducción de biomasa ≥92%, y rendimiento de soja >2,200 kg ha−1. Promediando los programas de herbicidas, el control de A. rudis al momento de la cosecha fue 84%, y la densidad fue 15 plantas m−2 con programas de herbicidas PRE fb POST en comparación con 42% de control y densidad de 101 plantas m−2 con programas de sólo herbicidas POST. Los resultados de este estudio indicaron que existen programas de herbicidas PRE fb POST con modos de acción efectivos para el control de A. rudis resistente a glyphosate durante toda la temporada de crecimiento en soja resistente a glyphosate.

Control of Glyphosate-Resistant Common Waterhemp (Amaranthus rudis) in Glufosinate-Resistant Soybean

Glyphosate-resistant (GR) common waterhemp has become a significant problem weed in Nebraska and several Midwestern states. Several populations of GR common waterhemp are also resistant to acetolactate synthase (ALS)-inhibiting herbicides, making them difficult to control with POST herbicides in GR soybean. Glufosinate-resistant (GFR) soybean is an alternate system for controlling GR common waterhemp, justifying the need for evaluating glufosinate-based herbicide programs. The objectives of this study were to compare POST-only herbicide programs (including one-pass and two-pass POST programs) with PRE followed by (fb) POST herbicide programs for control of GR common waterhemp in GFR soybean and their effect on common waterhemp density, biomass, and soybean yield. Field experiments were conducted in 2013 and 2014 near Fremont, NE in a growers field infested with GR common waterhemp. Glufosinate applied early- and late-POST provided 76% control of GR common waterhemp at 14 d after late-POST (DALPOST) compared with 93% control with a PRE fb POST program when averaged across treatments. The PRE application of chlorimuron plus thifensulfuron plus flumioxazin, S-metolachlor plus fomesafen or metribuzin, saflufenacil plus dimethenamid-P fb glufosinate provided ≥95% control of common waterhemp throughout the growing season, reduced common waterhemp density to ≤2.0 plants m−2, caused ≥94% biomass reduction, and led to 1,984 to 2,210 kg ha−1 soybean yield. Averaged across treatments, the PRE fb POST program provided 82% common waterhemp control at soybean harvest, reduced density to 23 plants m−2 at 14 DALPOST, and caused 86% biomass reduction and 1,803 kg ha−1 soybean yield compared with 77% control, 99 plants m−2, 53% biomass reduction, and 1,190 kg ha−1 yield with POST-only program. It is concluded that PRE fb POST programs with multiple effective modes of action are available for control of GR common waterhemp in GFR soybean. Nomenclature: Acetochlor; alachlor; cloransulam; chlorimuron; dimethenamid; flumioxazin; fomesafen; glufosinate; glyphosate; imazethapyr; metribuzin; saflufenacil; S-metolachlor; sulfentrazone; thifensulfuron; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr. Amaranthus rudis resistente a glyphosate (GR) se ha convertido en un problema de malezas significativo en Nebraska y en varios estados del Medio Oeste. Varias poblaciones de A. rudis GR también son resistentes a herbicidas inhibidores de acetolactate synthase, lo que las hace difíciles de controlar con herbicidas POST en soja GR. Soja resistente a glufosinate es un sistema alternativo para el control de A. rudis GR, lo que justifica la necesidad de evaluar programas de herbicidas basados en glufosinate. Los objetivos de este estudio fueron comparar programas con sólo herbicidas POST (incluyendo programas POST con uno y dos pases) con programas de herbicidas PRE seguidos por (fb) POST para el control de A. rudis GR en soja GFR y sus efectos sobre la densidad y biomasa de A. rudis y el rendimiento de la soja. En 2013 y 2014, se realizaron experimentos de campo cerca de Fremont, Nebraska en un campo comercial infestado con A. rudis GR. Glufosinate aplicado en POST temprano y tardío brindó 76% de control de A. rudis GR a 14 d después del POST tardío (DALPOST), comparado con 93% de control con un programa PRE fb POST, cuando se promediaron los tratamientos. Las aplicaciones PRE de chlorimuron más thifensulturon más flumioxazin, S-metolachlor más fomesafen o metribuzin, saflufenacil más dimethenamid-P fb glufosinate brindaron ≥95% de control de A. rudis a lo largo de la temporada de crecimiento, redujeron la densidad de A. rudis a ≤2 plantas m−2, causaron ≥94% de reducción de biomasa, y permitieron un rendimiento de soja de 1,984 a 2,210 kg ha−1. Al promediarse los tratamientos, el programa PRE fb POST brindó 82% de control de A. rudis al momento de la cosecha, redujo la densidad a 23 plantas m−2 a 14 DALPOST, causó 86% de reducción de biomasa, y el rendimiento de la soja fue 1,803 kg ha−1, comparado con 77% de control, 99 plantas m−2, 53% de reducción de biomasa, y un rendimiento de 1,190 kg ha−1 con el programa de sólo herbicidas POST. Se concluyó que hay programas de herbicidas PRE fb POST disponibles con modos de acción efectivos para el control de A. rudis GR en soja GFR.

A Statewide Survey of Stakeholders to Assess the Problem Weeds and Weed Management Practices in Nebraska

Abstract Stakeholders were surveyed across Nebraska to identify the problem weeds and assess common weed management practices. A total of 425 responses were returned across four Nebraska extension districts (Northeast, Panhandle, Southeast, and West Central). Collectively, 61.2% of total farmed or scouted areas in Nebraska were under no-till production, and corn and soybean were the major crops (82.3% of total farmed or scouted area). Common waterhemp, horseweed, and kochia were the most problematic weeds statewide. Widespread occurrence of glyphosate-resistant (GR) weeds such as common waterhemp, horseweed, kochia, and Palmer amaranth were a serious problem in GR crop production. Additionally, 60% of growers in Nebraska reported the presence of at least one GR weed species on their farms. The most commonly used preplant burndown herbicides were 2,4-D and glyphosate, followed by saflufenacil and dicamba. In Nebraska, 74% and 59% of corn and soybean growers, respectively, were using PRE herbicides; however, more than 80% of growers were using POST herbicides for in-crop weed management. Atrazine alone or in premix or tank mix with mesotrione, S-metolachlor, or acetochlor were the most widely applied PRE herbicides in corn and grain sorghum, whereas the most commonly used PRE herbicides in soybean were the inhibitors of acetolactate synthase (ALS) and protoporphyrinogen oxidase (PPO). Glyphosate was the most frequent choice of the survey respondents as a POST herbicide in GR corn and soybean; 2,4-D was the most commonly used POST herbicide in grain sorghum and wheat. In Nebraska, only 5.2% of total crop area was planted with glufosinate-resistant crops. Most of the respondents (89%) were aware of the new multiple herbicide–resistant crops, and 80% of them listed physical drift and volatility of the auxinic herbicides as their primary concern. Fortyeight percent of survey respondents identified herbicide-resistant weed management as their primary research and extension priority. Nomenclature: 2,4-D; acetochlor; atrazine; glufosinate; glyphosate; mesotrione; S-metolachlor; common waterhemp, Amaranthus rudis J.D. Sauer; horseweed, Conyza canadensis (L.) Cronq.; kochia, Kochia scoparia (L.) Schrad.; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench ssp. bicolor; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Palmer Amaranth (Amaranthus palmeri) and Velvetleaf (Abutilon theophrasti) Control in No-Tillage Conventional (Non–genetically engineered) Soybean Using Overlapping Residual Herbicide Programs

Abstract Due to depressed corn and soybean prices over the last few years in the United States, growers in Nebraska are showing interest in no-tillage (hereafter referred to as no-till) conventional (non–genetically engineered [non-GE]) soybean production. Due to the increasing number of herbicide-resistant weeds in the United States, weed control in no-till non-GE soybean using POST herbicides is a challenge. The objectives of this study were to compare PRE-only, PRE followed by (fb) POST, and PRE fb POST with residual (POST-WR) herbicide programs for Palmer amaranth and velvetleaf control and soybean injury and yield, as well as to estimate the gross profit margins and benefit–cost ratio of herbicide programs. A field experiment was conducted in 2016 and 2017 at Clay Center, NE. The PRE herbicides tested in this study resulted in ≥95% Palmer amaranth and velvetleaf control at 28 d after PRE (DAPRE). Averaged across the programs, the PRE-only program controlled Palmer amaranth 66%, whereas 86% and 97% control was obtained with the PRE fb POST and PRE fb POST-WR programs, respectively, at 28 d after POST (DAPOST). At 28 DAPOST, the PRE fb POST herbicide programs controlled velvetleaf 94%, whereas the PRE-only program resulted in 85% control. Mixing soil-residual herbicides with foliar-active POST programs did not improve velvetleaf control. Averaged across herbicide programs, PRE fb POST programs increased soybean yield by 10% and 41% in 2016 and 2017, respectively, over the PRE-only programs. Moreover, PRE fb POST-WR programs produced 7% and 40% higher soybean yield in 2016 and 2017, respectively, compared with the PRE fb POST programs. The gross profit margin (US

Comparison of a premix of atrazine, bicyclopyrone, mesotrione, and S-metolachlor with other preemergence herbicides for weed control and corn yield in no-tillage and reduced-tillage production systems in Nebraska, USA

1,184.3 ha-1) was highest under flumioxazin/pyroxasulfone (PRE) fb fluthiacet-methyl plus S-metolachlor/fomesafen (POST-WR) treatment; however, the benefit–cost ratio was highest (6.1) with the PRE-only program of flumioxazin/chlorimuron-ethyl. Nomenclature: Chlorimuron-ethyl; flumioxazin; fluthiacetmethyl; fomesafen; pyroxasulfone; S-metolachlor; Palmer amaranth, Amaranthus Palmeri S. Watson; velvetleaf, Abutilon theophrasti Medik; corn, Zea mays L.; soybean, Glycine max (L.) Merr