Parminder S. Chahal

Herbicide Programs for Control of Glyphosate-Resistant Volunteer Corn in Glufosinate-Resistant Soybean

Abstract Glyphosate-resistant (GR) volunteer corn is a significant problem weed in soybean grown in rotation with corn in the midwestern United States and eastern Canada. The objective of this study was to evaluate the efficacy of glufosinate applied in single or sequential applications compared with acetyl-coenzyme A carboxylase (ACCase) inhibitors applied alone or tank mixed with glufosinate for controlling GR volunteer corn in glufosinate-resistant soybean. At 15 d after early-POST (DAEP), ACCase inhibitors applied alone controlled volunteer corn 76 to 93% compared to 71 to 82% control when tank mixed with glufosinate. The expected volunteer corn control achieved by tank mixing ACCase inhibitors and glufosinate was greater than the glufosinate alone, indicating that glufosinate antagonized ACCase inhibitors at 15 DAEP, but not at later rating dates. ACCase inhibitors applied alone or tank mixed with glufosinate followed by late-POST glufosinate application controlled volunteer corn and green foxtail ≥ 97% at 30 DAEP. Single early-POST application of glufosinate controlled common waterhemp and volunteer corn 53 to 78%, and green foxtail 72 to 93% at 15 DAEP. Single as well as sequential glufosinate applications controlled green foxtail and volunteer corn greater than or equal to 90%, and common waterhemp greater than 85% at 75 d after late-POST (DALP). Contrast analysis suggested that glufosinate applied sequentially provided greater control of volunteer corn at 15 and 75 DALP compared to a single application. Similar results were reflected in volunteer corn density and biomass at 75 DALP. Volunteer corn interference did not affect soybean yield, partly because of extreme weather conditions (hail and high winds) in both years of this study. Nomenclature: Clethodim; fenoxaprop-P; fluazifop-P; glufosinate; quizalofop-P; sethoxydim; common waterhemp, Amaranthus rudis Sauer; green foxtail, Setaria viridis (L.) Beauv.; soybean, Glycine max (L.) Merr.; volunteer corn, Zea mays L. Resumen El maíz voluntario resistente a glyphosate (GR) es un problema significativo de malezas en soja producida en rotación con maíz en el centro oeste de los Estados Unidos y en el este de Canadá. El objetivo de este estudio fue evaluar la eficacia de glufosinate aplicado solo o en aplicaciones secuenciales comparado con inhibidores de acetyl-coenzyme A carboxylase (ACCase) aplicados solos o en mezclas en tanque con glufosinate para el control de maíz GR voluntario en soja resistente a glufosinate. A 15 d después de la aplicación POST temprana (DAEP), los inhibidores de ACCase aplicados solos controlaron el maíz voluntario 76 a 93% comparado con 71 a 82% de control con la mezcla en tanque con glufosinate. El control esperado de maíz voluntario con las mezclas en tanque con ACCase y glufosinate fue mayor que el de glufosinate solo, lo que indicó que glufosinate antagonizó a los inhibidores de ACCase a 15 DAEP, pero no en fechas de evaluación posteriores. Los inhibidores de ACCase aplicados solos o en mezclas en tanque con glufosinate seguidos de aplicaciones tardías POST de glufosinate controlaron el maíz voluntario y Setaria viridis ≥ 97% a 30 DAEP. Aplicaciones POST tempranas de glufosinate solo controlaron Amaranthus rudis y maíz voluntario 53 a 78%, y S. viridis 72 a 93% a 15 DAEP. Aplicaciones solas y secuenciales de glufosinate controlaron S. viridis y maíz voluntario en 90% o más, y A. rudis más de 85% a 75 d después de la aplicación POST tardía (DALP). Análisis de contrastes sugirieron que glufosinate aplicado secuencialmente brindó mayor control del maíz voluntario a 15 y 75 DALP al compararse con una única aplicación. Resultados similares fueron observados en la densidad y biomasa del maíz voluntario a 75 DALP. La interferencia del maíz voluntario no afectó el rendimiento de la soja, parcialmente porque se presentaron condiciones extremas del estado del tiempo (granizo y vientos fuertes) en los dos años de este estudio.

Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Nebraska: Confirmation, EPSPS Gene Amplification, and Response to POST Corn and Soybean Herbicides

Palmer amaranth is the most problematic weed in agronomic crop production fields in the United States. A Palmer amaranth biotype was not controlled with sequential applications of glyphosate in glyphosate-resistant (GR) soybean production field in south-central Nebraska. The seeds of the putative GR Palmer amaranth biotype were collected in the fall of 2015. The objectives of this study were to (1) confirm GR Palmer amaranth and determine the level of resistance in a whole-plant dose-response bioassay, (2) determine the copy number of 5-enolpyruvylshikimate-3-phosphate (EPSPS) gene, the molecular target of glyphosate, and (3) evaluate the response of GR Palmer amaranth biotype to POST corn and soybean herbicides with different modes-of-action. Based on the effective dose required to control 90% of plants (ED90), the putative GR Palmer amaranth biotype was 37- to 40-fold resistant to glyphosate depending on the glyphosate-susceptible (GS) used as a baseline population. EPSPS gene amplification was present in the GR Palmer amaranth biotype with up to 32 to 105 EPSPS copies compared to the known GS biotypes. Response of GR Palmer amaranth to POST corn and soybean herbicides suggest reduced sensitivity to atrazine, hydroxyphenylpyruvate dioxygenase (HPPD)- (mesotrione, tembotrione, and topramezone), acetolactate synthase (ALS)- (halosulfuron-methyl), and protoporphyrinogen oxidase (PPO)- (carfentrazone and lactofen) inhibitors. GR Palmer amaranth was effectively controlled (>90%) with glufosinate applied at 593 g ai ha−1 with ≥95% reduction in biomass. More research is needed to determine whether this biotype exhibits multiple resistant to other group of herbicides and evaluate herbicide programs for effective management in corn and soybean. Nomenclature: 2,4-D; acetochlor; acifluorfen; atrazine; bentazon; bromoxynil; carfentrazone; chlorimuron; dicamba; fluthiacet; fomesafen; glufosinate; glyphosate; halosulfuron; imazamox; imazethapyr; lactofen; mesotrione; S-metolachlor; tembotrione; thiencarbazone; thifensulfuron; topramezone; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; soybean, Glycine max (L.) Merr. Amaranthus palmeri es la malezas más problemática en campos de producción de cultivos agronómicos en los Estados Unidos. Un biotipo de A. palmeri no fue controlado con aplicaciones secuenciales de glyphosate en un campo de producción de soja resistente a glyphosate (GR) en el sur central de Nebraska. Las semillas del biotipo putativo GR de A. palmeri fueron colectadas en el otoño de 2015. Los objetivos de este estudio fueron (1) confirmar que A. palmeri es GR y determinar el nivel de resistencia en un bioensayo de respuesta a dosis con plantas completas, (2) determinar el número de copias del gen 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), el objetivo molecular de glyphosate, y (3) evaluar la respuesta del biotipo GR de A. palmeri a herbicidas POST para maíz y soja con diferentes modos de acción. Con base en la dosis efectiva requerida para controlar 90% de las plantas (ED90), el biotipo putativo GR de A. palmeri fue 37 a 40 veces más resistente a glyphosate dependiendo de la población susceptible a glyphosate (GS) base utilizada. La amplificación del gen EPSPS estuvo presente en el biotipo GR de A. palmeri con 32 y hasta 105 copias más de EPSPS comparado con biotipos GS conocidos. La respuesta de A. palmeri GR a herbicidas POST para maíz y soja sugiere una sensibilidad reducida a atrazine, y a inhibidores de hydroxy phenylpyruvate dioxygenase (HPPD) (mesotrione, tembotrione, y topramezone), de acetolactate synthase (ALS) (halosulfuron-methyl), y de protoporphyrinogen oxidase (PPO) (carfentrazone y lactofen). A. palmeri GR fue efectivamente controlado (>90%) con glufosinate aplicado a 593 g ai ha−1 con ≥95% de reducción en la biomasa. Se necesita más investigación para determinar si este biotipo exhibe resistencia múltiple a herbicidas de otros grupos y para evaluar programas de herbicidas para su manejo efectivo en maíz y soja.

Herbicide-Resistant Palmer amaranth (Amaranthus palmeri S. Wats.) in the United States — Mechanisms of Resistance, Impact, and Management

Palmer amaranth, a dioecious summer annual species, is one of the most trouble‐ some weeds in the agronomic crop production systems in the United States. In the last two decades, continuous reliance on herbicide(s) with the same mode of action as the sole weed management strategy has resulted in the evolution of herbicideresistant (HR) weeds, including Palmer amaranth. By 2015, Palmer amaranth bio‐ types had been confirmed resistant to acetolactate synthase (ALS)-inhibitors, dinitroanilines, glyphosate, hydroxyphenylpyruvate dioxygenase (HPPD)-inhibi‐ tors, and triazine herbicides in some parts of the United States along with multiple HR biotypes. Mechanisms of herbicide-resistance in Palmer amaranth are discussed in this chapter. Preplant herbicide options including glufosinate, 2,4-D, and dicam‐ ba provide excellent Palmer amaranth control; however, their application is limited before planting crops, which is often not possible due to unfavorable weather con‐ ditions. Agricultural biotechnology companies are developing new multiple HR crops that will allow the post-emergence application of respective herbicides for management of HR weeds, including Palmer amaranth. For the effective in-crop management of Palmer amaranth, and to reduce the potential for the evolution of other HR weeds, growers should apply herbicides with different modes of action in tank-mixture and should also incorporate cultural practices including inversion till‐ age and cover crops along with herbicide programs.

Overlapping Residual Herbicides for Control of Photosystem (PS) II- and 4-Hydroxyphenylpyruvate Dioxygenase (HPPD)-Inhibitor-Resistant Palmer amaranth ( Amaranthus palmeri S. Watson) in Glyphosate-Resistant Maize

A Palmer amaranth (Amaranthus palmeri S. Watson) biotype has evolved resistance to photosystem (PS) II- (atrazine) and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides (mesotrione, tembotrione, and topramezone) in maize seed production field in Nebraska, USA. The objectives of this study were to determine the effect of soil residual pre-emergence (PRE) herbicides followed by (fb) tank-mixture of residual and foliar active post-emergence (POST) herbicides on PS-II- and HPPD-inhibitor-resistant Palmer amaranth control, maize yield, and net economic returns. Field experiments were conducted in a growers field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska, USA in 2015 and 2016. The contrast analysis suggested that saflufenacil plus dimethenamid-P or pyroxasulfone plus saflufenacil applied PRE provided 80–82% Palmer amaranth control compared to 65 and 39% control with saflufenacil and pyroxasulfone applied alone at 3 weeks after PRE (WAPRE), respectively. Among the PRE fb POST herbicide programs, 95–98% Palmer amaranth control was achieved with pyroxasulfone plus safluefenacil, or saflufenacil plus dimethenamid-P applied PRE, fb glyphosate plus topramezone plus dimethenamid-P plus atrazine, glyphosate plus diflufenzopyr plus dicamba plus pyroxasulfone, glyphosate plus diflufenzopyr plus pendimethalin, or glyphosate plus diflufenzopyr plus dicamba plus atrazine applied POST at 3 weeks after POST (WAPOST) through maize harvest. Based on contrast analysis, PRE fb POST programs provided 77–83% Palmer amaranth control at 3 WAPOST through maize harvest compared to 12–15% control with PRE-only and 66–84% control with POST-only programs. Similarly, PRE fb POST programs provided 99% biomass reduction at 6 WAPOST compared to PRE-only (28%) and POST-only (87%) programs. PRE fb POST programs provided higher maize yield (13,617 kg ha−1) and net return (US

Control of Photosystem II- and 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor-Resistant Palmer Amaranth (Amaranthus palmeri) in Conventional Corn

1,724 ha−1) compared to the PRE-only (2,656 kg ha−1; US

Evaluating Effect of Degree of Water Stress on Growth and Fecundity of Palmer amaranth (Amaranthus palmeri) Using Soil Moisture Sensors

285 ha−1) and POST-only (11,429 kg ha−1; US

Factors affecting germination and emergence of glyphosate-resistant hybrid corn (Zea mays L.) and its progeny

1,539 ha−1) programs. The results indicated that effective control of multiple herbicide-resistant Palmer amaranth can be achieved with PRE fb POST programs that include herbicides with overlapping residual activity to maintain season-long control.

Efficacy of Pre-Emergence and Post-Emergence Soybean Herbicides for Control of Glufosinate-, Glyphosate-, and Imidazolinone-Resistant Volunteer Corn

Abstract Palmer amaranth, a dioecious summer annual weed species, is the most troublesome weed in agronomic crop production systems in the United States. Palmer amaranth resistant to photosystem (PS) II- and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors is of particular concern in south central Nebraska. The objectives of this study were to determine the effect of PRE followed by POST herbicide programs on PS II- and HPPD-inhibitorresistant Palmer amaranth control, crop yield, and net economic return in conventional corn. A field study was conducted in 2014, 2015, and 2016 in a growers field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska. A contrast analysis suggested that mesotrione + S-metolachlor + atrazine applied PRE provided 83% Palmer amaranth control at 21 d after application compared to 78 and 72% control with pyroxasulfone + fluthiacet-ethyl + atrazine and saflufenacil + dimethenamid-P, respectively. Most of the PRE followed by POST herbicide programs provided ≥85% Palmer amaranth control. Based on contrast analysis, POST application of dicamba +diflufenzopyr provided 93% Palmer amaranth control compared to 87, 79, and 42% control with dicamba, dicamba + halosulfuron, and acetochlor, respectively, at 28 d after POST. All PRE followed by POST herbicide programs, aside from mesotrione + S-metolachlor + atrazine followed by acetochlor (2,530 to 7,809 kg ha-1), provided 9,550 to 10,500 kg ha-1 corn yield compared with 2,713 to 6,110 kg ha-1 from nontreated control. Similarly, PRE followed by POST herbicide programs, except for mesotrione + S-metolachlor + atrazine followed by acetochlor (

Growth Stage Affects Dose Response of Selected Glyphosate-Resistant Weeds to Premix of 2,4-D Choline and Glyphosate (Enlist Duo™ Herbicide*)

191 and

Glyphosate-Resistant Weed Control and Soybean Injury in Response to Different PPO-Inhibiting Herbicides

897 ha-1), provided similar net return of