Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-05-23T14:07:42.328Z Has data issue: false hasContentIssue false

Effect of herbicide programs on control and seed production of multiple herbicide–resistant Palmer amaranth (Amaranthus palmeri) in corn resistant to 2,4-D/glufosinate/glyphosate

Published online by Cambridge University Press:  16 April 2024

Ramandeep Kaur
Affiliation:
Graduate Research Assistant, Department of Agronomy and Horticulture, University of Nebraska–Lincoln, Lincoln, NE, USA
Rachel Rogers
Affiliation:
Graduate Research Assistant, Department of Statistics, University of Nebraska–Lincoln, Lincoln, NE, USA
Nevin C. Lawrence
Affiliation:
Associate Professor, Panhandle Research Extension and Education Center, Scottsbluff, NE, USA
Yeyin Shi
Affiliation:
Associate Professor, Department of Biological Systems Engineering, University of Nebraska–Lincoln, Lincoln, NE, USA
Parminder S. Chahal
Affiliation:
Field Development Representative, FMC Agricultural Solutions, Gretna, NE, USA
Stevan Z. Knezevic
Affiliation:
Professor, Department of Agronomy and Horticulture, University of Nebraska–Lincoln, Lincoln, NE, USA
Amit J. Jhala*
Affiliation:
Professor & Associate Department Head, Department of Agronomy and Horticulture, University of Nebraska–Lincoln, Lincoln, NE, USA
*
Corresponding author: Amit J. Jhala; Email: Amit.Jhala@unl.edu
Rights & Permissions [Opens in a new window]

Abstract

Multiple herbicide–resistant (MHR) Palmer amaranth is among the most problematic summer annual broadleaf weeds in Nebraska and several other states. A new MHR corn cultivar (resistant to 2,4-D/glufosinate/glyphosate, also known as Enlist corn) has been commercially available in the United States since 2018. Growers are searching for herbicide programs for control and reduce seed production of MHR Palmer amaranth among Enlist corn crops. The objectives of this study were to evaluate herbicides applied preemergence, early postemergence, or preemergence followed by (fb) late postemergence for the management of MHR Palmer amaranth in Enlist corn fields and to assess their effect on Palmer amaranth biomass, density, seed production, and corn yield. Field experiments were conducted near Carleton, NE, in 2020 and 2021, in a grower’s field of Enlist corn infested with acetolactate synthase–inhibitor/atrazine/glyphosate–resistant Palmer amaranth. Herbicides applied preemergence, such as flufenacet/isoxaflutole/thiencarbazone-methyl, acetochlor/clopyralid/flumetsulam, or acetochlor/clopyralid/mesotrione, provided 75% to 99% control of Palmer amaranth 30 d after preemergence. Preemergence fb late postemergence herbicides resulted in 94% Palmer amaranth control 90 d after late postemergence, reduced weed density to 0 to 8 plants m−2 30 d after late postemergence, and reduced biomass to 2 to 14 g m−2 15 d after late postemergence compared to preemergence-only (59% control, 0 to 15 plants m−2, and 4 to 123 g m−2) and early postemergence–only herbicides (78% control, 6 to 30 plants m−2, and 8 to 25 g m−2). Based on contrast analysis, Palmer amaranth seed production was reduced to 14,050 seeds m–2 in preemergence fb late postemergence herbicide programs compared with 325,490 seed m–2 in preemergence-only and 376,750 seed m–2 in early postemergence–only programs. Based on orthogonal contrast, higher corn yield of 12,340 and 11,730 kg ha−1 was obtained with preemergence fb late postemergence herbicide programs compared with preemergence-only (10,840 and 11,510 kg ha−1) and early postemergence–only programs (10,850 and 10,030 kg ha−1) in 2020 and 2021, respectively.

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of Weed Science Society of America

Introduction

Palmer amaranth is among the most problematic summer annual broadleaf weeds across the mid-south, southeastern, mid-Atlantic, and north central United States (Oliveira et al. Reference Oliveira, Jhala, Bernards, Proctor, Stepanovic and Werle2022; Vencill et al. Reference Vencill, Grey, Culpepper, Gaines and Westra2008). In a survey conducted by the Weed Science Society of America, Palmer amaranth was ranked as the most troublesome weed in agronomic cropping systems in the United States (Van Wychen Reference Van Wychen2022). A widespread occurrence of Palmer amaranth is due to its unique biological attributes that include an extended period of emergence, aggressive growth rate, high photosynthetic rate, high water-use efficiency, considerable biomass accumulation, prolific seed production (up to 0.6 million seed per female plant) (Chahal et al. Reference Chahal, Irmak, Jugulam and Jhala2018b; Jha and Norsworthy Reference Jha and Norsworthy2009; Ward et al. Reference Ward, Webster and Steckel2013), and dioecious reproductive biology, which increases the pollen-mediated gene flow and spread of herbicide resistance alleles (Jhala et al. Reference Jhala, Norsworthy, Ganie, Sosnoskie, Beckie, Mallory-Smith, Liu, Wei, Wang and Stoltenberg2021). If not controlled, Palmer amaranth can cause a significant crop yield reduction. For example, a Palmer amaranth density of 3 plants m−2 caused 60% yield loss of soybean (Glycine max L. Merill) in a study conducted in Arkansas (Klingaman and Oliver Reference Klingaman and Oliver1994). Bensch et al. (Reference Bensch, Horak and Peterson2003) reported 78% soybean yield loss at a density of 8 plants m−2 in Kansas. Massinga et al. (Reference Massinga, Currie, Horak and Boyer2001) reported that Palmer amaranth at 0.5 to 8 plants m−1 row reduced corn yield from 11% to 91%.

In addition to its biological characteristics, the evolution of herbicide-resistant Palmer amaranth in agronomic cropping systems has become a challenge for growers for effective management (Chahal et al. Reference Chahal, Ganie and Jhala2018a; Mausbach et al. Reference Mausbach, Irmak, Sarangi, Lindquist and Jhala2021). Palmer amaranth has evolved resistance to herbicides from several site-of-action (SOA) groups, including those that inhibit acetolactate synthase (ALS), 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS), microtubule assembly, photosystem II, protoporphyrinogen oxidase (PPO) (Chahal et al. Reference Chahal, Varanasi, Jugulam and Jhala2017; Garetson et al. Reference Garetson, Singh, Singh, Dotray and Bagavathiannan2019; Ward et al. Reference Ward, Webster and Steckel2013), 4-hydroxyphenyl pyruvate dioxygenase (HPPD) (Chahal et al. Reference Chahal, Aulakh, Mithila and Jhala2015; Jhala et al. Reference Jhala, Sandell, Rana, Kruger and Knezevic2014), synthetic auxins (Kumar et al. Reference Kumar, Liu, Boyer and Stahlman2019), and very long chain fatty acids (Brabham et al. Reference Brabham, Norsworthy, Houston, Varanasi and Barber2019). A Palmer amaranth biotype that is resistant to glufosinate has been confirmed in Arkansas (Priess et al. Reference Priess, Norsworthy, Godara, Mauromoustakos, Butts, Roberts and Barber2022) and dicamba-resistant Palmer amaranth was reported in Tennessee in 2021 (Foster and Steckel Reference Foster and Steckel2022). In addition to resistance to herbicides with a single SOA, Palmer amaranth resistance to multiple herbicides with different SOAs has been reported. One of the most prevalent forms of multiple herbicide resistance in Palmer amaranth is resistance to glyphosate and ALS-inhibiting herbicides, which has been confirmed in eight states (Chahal et al. Reference Chahal, Varanasi, Jugulam and Jhala2017; Heap Reference Heap2024; Jhala et al. Reference Jhala, Sandell, Rana, Kruger and Knezevic2014). In addition, Palmer amaranth that is resistant to atrazine, chlorsulfuron, 2,4-D, glyphosate, and mesotrione has been reported in Kansas (Kumar et al. Reference Kumar, Liu, Boyer and Stahlman2019; Reference Kumar, Liu and Stahlman2020). Kohrt et al. (Reference Kohrt, Sprague, Nadakuduti and Douches2016) confirmed Palmer amaranth resistance to ALS inhibitor, atrazine, and glyphosate in Michigan. As of March 2024, Palmer amaranth has evolved resistance to 10 herbicide SOAs (Heap Reference Heap2024).

Palmer amaranth has an extended emergence pattern from early May through August in the Midwest (Chahal et al. Reference Chahal, Barnes and Jhala2021), and from late April to early September in the southern United States (Liu et al. Reference Liu, Kumar, Jha and Stahlman2022), making it difficult to control with herbicides applied preemergence only or postemergence only (Mausbach et al. Reference Mausbach, Irmak, Sarangi, Lindquist and Jhala2021; Shyam et al. Reference Shyam, Chahal, Jhala and Jugulam2021b). Herbicides applied preemergence generally lose their residual activity 20 to 40 d after application depending on the herbicide used and soil type; however, most postemergence herbicides commonly applied to corn have minimal to no soil residual activity (Wiggins et al. Reference Wiggins, McClure, Hayes and Steckel2015). The late-emerging Palmer amaranth often escapes a postemergence herbicide and produces seed, leading to the replenishment of the soil seedbank (Bagavathiannan and Norsworthy Reference Bagavathiannan and Norsworthy2012). Therefore, herbicide practices should be focused on season-long control of Palmer amaranth to reduce seed production and infestation during subsequent crop seasons (Striegel and Jhala Reference Striegel and Jhala2022). In addition, soil residual herbicides such as acetochlor, dimethenamid-P, fluthiacet-methyl, or pyroxasulfone can be applied with a foliar-active postemergence herbicide to corn up to certain growth stages to provide overlapping residual activity to control weeds (Jhala et al. Reference Jhala, Malik and Willis2015; McDonald et al. Reference McDonald, Sarangi, Rees and Jhala2023; Sarangi and Jhala Reference Sarangi and Jhala2019).

A new multiple herbicide–resistant (MHR) corn trait that is resistant to 2,4-D, glufosinate, and glyphosate, also known as Enlist corn, has been commercially available in the United States since 2018. It provides an opportunity for management of ALS-, PS II-, and EPSPS-inhibitor-resistant Palmer amaranth with the aid of herbicide practices that cannot be applied to conventional or glyphosate-resistant corn. The objectives of this study were to evaluate the effect of herbicides applied preemergence, early postemergence, and preemergence fb late postemergence for control of ALS-inhibitor/atrazine/glyphosate-resistant Palmer amaranth, and their effect on Palmer amaranth density, biomass, seed production, crop injury, and yield in Enlist corn crops. We hypothesized that a season-long control of MHR Palmer amaranth would be achieved with reduced seed production in a preemergence fb a late postemergence herbicide application program.

Materials and Methods

Field Experiments

Field experiments were conducted in 2020 and 2021 in a grower’s field infested with ALS-inhibitor/atrazine/glyphosate-resistant Palmer amaranth near Carleton, NE (40.30°N, 97.67°W). The experiments were established under no-till conditions. The previous crops at the site were no-till soybean in 2019 and no-till corn in 2020. Palmer amaranth was the dominant summer weed at the experimental site and was confirmed to be resistant to ALS-inhibitor/atrazine/glyphosate (Chahal et al. Reference Chahal, Varanasi, Jugulam and Jhala2017). The soil at the experimental site was a silt loam (montmorillonitic, mesic, Pachic Argiustolls), with 19% sand, 63% silt, 18% clay, pH 6.0, and 2.5% organic matter content. The herbicide 2,4-D (Enlist ONE; Corteva Agriscience, Indianapolis, IN) was applied in early spring to control glyphosate-resistant horseweed (Erigeron canadensis L. Cronq.) that was present at the experimental site. The treatments were laid out in a randomized complete block design with four replications. The dimensions of individual experimental plots were 3 m wide and 9 m long. Enlist E3 corn (8097 SXE Enlist Corn SmartStax; Corteva AgriScience, Indianapolis, IN) was planted at 67,500 seed ha−1 on May 12, 2020, and May 18, 2021, in 78-cm-row spacing. The experimental site setup was without supplemental irrigation. Precipitation received during the crop growing season for both years is listed in Table 1.

Table 1. Monthly mean air temperature and total precipitation during the 2020 and 2021 growing seasons along with the 30-yr average at the experiment site near Carleton, NE. a

a Data were obtained from the National Oceanic and Atmospheric Administration.

Herbicides to control Palmer amaranth were applied preemergence only, early postemergence only, and preemergence fb late postemergence with a total of 15 treatments, including a nontreated control and a weed-free control for comparison purpose (Table 2). Herbicides were applied using a handheld CO2-pressurized backpack sprayer equipped with TeeJet AIXR 110015 flat-fan nozzles (Spraying Systems Co., Glendale, IL) calibrated to deliver a flow rate of 140 L ha−1 at 276 kPa at a constant speed of 4.8 km h−1. Glufosinate was mixed with liquid ammonium sulfate at 3% vol/vol (Anonymous 2017) and was applied with TeeJet XR 11005 flat-fan nozzles (Spraying Systems Co.). The preemergence herbicides were applied 2 d after corn planting on May 14, 2020, and on the day of corn planting on May 18, 2021. Early postemergence herbicides were applied 36 d after corn planting on June 18, 2020, and 28 d after corn planting on June 16, 2021; and late postemergence herbicides were applied on June 23, 2020, and on June 25, 2021. Early postemergence and late postemergence herbicides were applied when Palmer amaranth was 10 to 15 cm and 20 to 30 cm tall, respectively. The height of Palmer amaranth was variable because of its extended emergence pattern.

Table 2. Herbicides, application timings, and rates used for control of acetolactate synthase inhibitor/atrazine/glyphosate–resistant Palmer amaranth in a 2,4-D/glufosinate/glyphosate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021.

a Glufosinate treatments were mixed with liquid ammonium sulfate (N PAK AMS, Winfield United, Arden Hills, MN) at 3% vol/vol.

b Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; POST, postemergence; PRE, preemergence.

Data Collection

Visible estimates of Palmer amaranth control were recorded 15 and 30 d after preemergence and after early postemergence, and 15, 30, and 90 d after late postemergence using a 0% to 100% scale, with 0% meaning no Palmer amaranth control and 100% meaning complete control. Corn injury was assessed on a 0% to 100% scale 15 and 30 d after each application with 0% meaning no corn injury and 100% meaning plant death. Palmer amaranth density was recorded by counting the number of Palmer amaranth plants in 0.5-m2 quadrats from each plot 15 and 30 d after preemergence, 30 d after early postemergence, and 30 d after late postemergence. Aboveground biomass was collected from 0.5-m2 quadrats plot−1 30 d after early postemergence and 15 d after late postemergence. Palmer amaranth plants were clipped at the soil surface, kept in paper bags, dried at 65 C in an oven for a week, and weighed. Palmer amaranth seed production was recorded by placing a 1.0-m2 quadrat in the center two rows of corn and collecting the inflorescences of female plants from each quadrat. Palmer amaranth inflorescences were stripped from the stems and separated by passing them through a series of USA standard testing sieves (Gilson Company, Worthington, OH) with mesh size ranging from 0.50 to 3.35 mm. Material collected from the 0.50-mm sieve was processed with a seed cleaner (Hoffman Manufacturing, Albany, OR) that used air to remove the lighter floral chaff from the Palmer amaranth seed (Sosnoskie et al. Reference Sosnoskie, Webster, Grey and Culpepper2014). The seeds were thoroughly cleaned, weighted, and number of seeds per square meter was determined. At maturity, corn was harvested from the center two rows of each plot using a plot combine, weighed, and the moisture content was recorded. The grain yield was adjusted to 15.5% moisture content and converted into kilograms per hectare (kg ha−1).

Statistical Analysis

Palmer amaranth control, density, aboveground biomass, and Palmer amaranth seed production, as well as corn yield data, were subjected to ANOVA using the GLIMMIX procedure with SAS software (version 9.4; SAS Institute Inc, Cary, NC). Before analysis, data were subjected to the UNIVARIATE procedure for testing normality and homogeneity of variance with normal Q-Q plots and Levene’s test, respectively. Type III tests were used to assess fixed effects, and treatment comparisons were made based on Tukey Kramer’s pairwise comparison test and Sidak adjustments. Palmer amaranth control data were log transformed and fit to generalized linear mixed-effect models using the GLIMMIX procedure with beta distribution. Palmer amaranth density and biomass data were square root–transformed, and back-transformed values are presented. Palmer amaranth seed production and corn yield data were analyzed with the GLIMMIX procedure using gaussian (link = “identity”) error distributions selected for response variables based on the restricted maximum likelihood technique. Year and herbicide treatments were considered fixed effects in the model, while replications were considered a random effect. Orthogonal contrasts were considered to compare herbicide programs (preemergence vs. early postemergence, preemergence vs. preemergence fb late postemergence, and early postemergence vs. preemergence fb late postemergence) at P ≤ 0.05 for Palmer amaranth control at 15 and 30 d after early postemergence; 15, 30, and 90 d after late postemergence; Palmer amaranth seed production; and corn yield.

Results and Discussion

Year-by-treatment interaction for Palmer amaranth control, aboveground biomass, and seed production was not significant (P ≥ 0.05); therefore, data from both years were combined. Year-by-treatment interaction for Palmer amaranth density and corn yield was significant; therefore, data are presented separately for both years. No corn injury was observed from any herbicide program (data not shown), indicating that the herbicides evaluated in this study are safe to use in Enlist corn when applied according to label instructions.

Temperature and Precipitation

The average monthly temperature during the 2021 growing season was higher than 2020, except June and July (Table 1). Below-average precipitation of 13.5 mm fell in June and 45.5 mm in July 2021, while above-average precipitation of 147.6 mm in occurred June and 424.2 mm in July occurred in 2020 compared to the 30-yr average of 115.1 mm and 105.2 mm for June and July, respectively.

Palmer Amaranth Control

Herbicides applied preemergence in this study provided ≥96% control of Palmer amaranth 15 d after preemergence, and 75% to 99% control 30 d after preemergence, without difference among treatments (Table 3). The residual activity of most herbicides applied preemergence declined as the season progressed. For example, acetochlor/clopyralid/flumetsulam, and flufenacet/isoxaflutole/thiencarbazone-methyl controlled Palmer amaranth by 44% at 90 d after late postemergence compared with 87% control with acetochlor/clopyralid/mesotrione (Table 3). Rain fell within 10 d of applying preemergence herbicides in both years with an average of 80.3 mm in 2020 and 81.5 mm in 2021, which was comparatively less than the 30-yr average of 135.4 mm for May (Table 1).

Table 3. Control of multiple herbicide–resistant Palmer amaranth affected by herbicide programs in a 2,4-D/glufosinate/glyphosate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021. a

a Abbreviations: DA-PRE, days after preemergence application; DA-EPOST, days after early postemergence application; DA-LPOST, days after late postemergence application; EPOST, early postemergence; fb, followed by; LPOST, late postemergence; NS, not significant.

b Year-by-treatment interaction for Palmer amaranth control was nonsignificant; therefore, data were pooled across both years (2020 and 2021).

c Means presented within each column with no common letters are significantly different as according to the Tukey Kramer pairwise comparison test.

d A priori orthogonal contrasts.

e P < 0.0001.

Among the early postemergence herbicides, 2,4-D + glufosinate controlled Palmer amaranth by 90%; and glufosinate provided 83% control compared with 57% control with glyphosate/2,4-D; and 62% control with 2,4-D 15 d after early postemergence (Table 3). Glufosinate + 2,4-D and glyphosate/2,4-D provided similar Palmer amaranth control, ranging from 71% to 78% at 30 d after early postemergence and 82% to 84% at 30 d after late postemergence, respectively. As the season progressed, Palmer amaranth control with glufosinate alone decreased to 66% compared to 85% with 2,4-D + glufosinate, 82% with glyphosate/2,4-D, and 80% with 2,4-D alone 90 d after late postemergence (Table 3).

Herbicides applied preemergence without a follow-up postemergence herbicide could not provide economically acceptable Palmer amaranth control compared with preemergence fb late postemergence herbicide programs later in the season, except for acetochlor/clopyralid/mesotrione. This is because Palmer amaranth at the study site was resistant to the ALS inhibitor. Thus, lower Palmer amaranth control was obtained with acetochlor/clopyralid/flumetsulam, and flufenacet/isoxaflutole/thiencarbazone-methyl applied preemergence because both premixes contain an ALS inhibitor. Palmer amaranth was not resistant to acetochlor/clopyralid/mesotrione. A similar decline in residual activity of soil-applied preemergence herbicides has been reported with soybean in multiyear field studies in Nebraska, where preemergence herbicides resulted in 66% control of Palmer amaranth compared with 86% control by preemergence fb late postemergence herbicide programs 28 d after late postemergence (Sarangi and Jhala Reference Sarangi and Jhala2019). Liu et al. (Reference Liu, Kumar, Jhala, Jha and Stahlman2021) concluded that a preemergence fb late postemergence herbicide routine resulted in 83% Palmer amaranth control 7 wk after late postemergence compared to 67% control with a preemergence-only application to glufosinate/glyphosate-resistant corn.

The preemergence fb late postemergence herbicide routine provided ≥94% control of Palmer amaranth 15 d after late postemergence, and 87% to 97% control 90 d after late postemergence without difference among treatments (Table 3). This was attributed to an early-season control of Palmer amaranth by the residual activity of preemergence herbicides, whereas the late-emerged flushes of Palmer amaranth were controlled by a follow-up application of late postemergence herbicides. The preemergence fb late postemergence herbicide programs provided similar Palmer amaranth control (87% to 97%) 90 d after late postemergence. While Palmer amaranth is known for its extended emergence pattern, emergence is reported to be higher from early May to mid-July (Chahal et al. Reference Chahal, Barnes and Jhala2021). Meyer et al. (Reference Meyer, Norsworthy, Young, Steckel, Bradley, Johnson, Loux, Davis, Kruger, Bararpour, Ikley, Spaunhorst and Butts2015) showed that auxin-based late postemergence herbicides can control glyphosate-resistant Palmer amaranth in soybean fields.

Contrast analysis showed that preemergence fb late postemergence herbicide programs resulted in 94% Palmer amaranth control compared with 59% and 78% control with preemergence-only and early postemergence–only programs, respectively (Table 3). Similarly, Sarangi et al. (Reference Sarangi, Sandell, Kruger, Knezevic, Irmak and Jhala2017) reported 90% control of herbicide-resistant Amaranthus species in soybean fields with a preemergence fb late postemergence herbicide regimen. Several other studies have found greater control of Amaranthus species with preemergence fb late postemergence herbicide applications compared with preemergence-only or early postemergence–only applications (Aulakh and Jhala Reference Aulakh and Jhala2015; Johnson et al. Reference Johnson, Breitenbach, Behnken, Miller, Hoverstad and Gunsolus2012; Liu et al. Reference Liu, Kumar, Jhala, Jha and Stahlman2021; Striegel and Jhala Reference Striegel and Jhala2022).

Palmer Amaranth Density and Biomass

Year-by-treatment interaction for Palmer amaranth density was significant, thus Palmer amaranth density data were presented separately by year. Year-by-treatment interaction for Palmer amaranth biomass data were nonsignificant, so data were combined across both years. Palmer amaranth density and biomass were affected by the herbicide programs compared with the nontreated control (Table 4). Palmer amaranth emergence was greater in 2020 than in 2021. For example, Palmer amaranth density in the nontreated control ranged from 61 to 149 plants m−2 in 2020 compared with 43 to 72 plants m−2 in 2021. This was most likely due to more precipitation and low temperature in 2020 compared with 2021, particularly in June 2020, when 147.6 mm of rainfall provided plenty of moisture for Palmer amaranth emergence and growth (Table 1).

Table 4. Multiple herbicide–resistant Palmer amaranth density and above-ground biomass as affected by the herbicide programs in a 2,4-D/glyphosate/glufosinate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021. a,b

a Abbreviations: DA-PRE, days after preemergence application; DA-EPOST, days after early postemergence application; DA-LPOST, days after late postemergence application; EPOST, early postemergence; fb, followed by; LPOST, late postemergence.

b Year by treatment interaction for Palmer amaranth density was significant; therefore, data are presented separately for both years (2020 and 2021).

c Means presented within each column with no common letters are significantly different according to the Tukey Kramer pairwise comparison test. Year-by-treatment for Palmer amaranth biomass was nonsignificant; therefore, data were combined across both years.

d Year-by-treatment interaction for Palmer amaranth biomass was nonsignificant; therefore, data of both years were combined.

e Palmer amaranth density data were not collected at 30 d after late postemergence herbicide application in 2020; therefore, data from only 2021 are presented.

At 30 d after preemergence, acetochlor/clopyralid/mesotrione, acetochlor/clopyralid/flumetsulam, and flufenacet/isoxaflutole/thiencarbazone-methyl resulted in Palmer amaranth densities of 0 to 5, 10 to 66, and 2 to 47 plants m−2, respectively, during both years (Table 4). As the season progressed, the efficacy of preemergence herbicides was reduced, except acetochlor/clopyralid/mesotrione, which reduced Palmer amaranth density to 0 to 2 plants m−2 at 30 d after early postemergence. Among early postemergence herbicides, 2,4-D resulted in a Palmer amaranth density of 9 and 17 plants m−2 in 2020 and 2021, respectively, whereas 2,4-D + glufosinate and glufosinate applied alone resulted in a Palmer amaranth density of 6 and 9 plants m−2 in 2021, respectively. Adequate soil moisture at the beginning of the season favors the germination of Palmer amaranth and, due to the lack of preemergence herbicide, provides an opportunity for Palmer amaranth to emerge and compete with corn. Palmer amaranth was at a variable height when early postemergence herbicides were applied, and it is known that the efficacy of auxinic herbicides, as well as glufosinate, can vary with weed height and density (Barnett et al. Reference Barnett, Culpepper, York and Steckel2013; Jhala et al. Reference Jhala, Sandell, Sarangi, Kruger and Knezevic2017; Steckel et al. Reference Steckel, Wax, Simmons and Phillips1997).

Among preemergence fb late postemergence herbicide programs, acetochlor/clopyralid/mesotrione fb 2,4-D; acetochlor/clopyralid/flumetsulam fb glufosinate; or flufenacet/isoxaflutole/thiencarbazone-methyl fb glufosinate recorded no Palmer amaranth plants 30 d after late postemergence. Chahal and Jhala (Reference Chahal and Jhala2015) observed just one Amaranthus plant per square meter with glufosinate applied early postemergence fb late postemergence 45 d after late postemergence compared with 6 plants m−2 in the nontreated control in glufosinate-resistant soybean in Nebraska. Among the preemergence fb late postemergence herbicide programs, acetochlor/clopyralid/flumetsulam fb 2,4-D resulted in higher Palmer amaranth density (8 plants m−2) 30 d after late postemergence, most likely due to declining residual activity of the preemergence herbicide and uneven Palmer amaranth height when 2,4-D was applied. The preemergence fb late postemergence herbicide applications recorded 0 to 8 Palmer amaranth plants m−2 compared with 6 to 30 and 0 to 15 plants m−2 with early postemergence-only and preemergence-only herbicides, respectively, 30 d after late postemergence (Table 4). Thus, the late postemergence herbicide caused a 50% density reduction compared with the preemergence-only herbicides. Norsworthy et al. (Reference Norsworthy, Korres, Walsh and Powles2016) and Aulakh and Jhala (Reference Aulakh and Jhala2015) have explained that preemergence fb late postemergence herbicide applications were more effective than early postemergence–only or preemergence-only herbicides due to multiple herbicide application timings and the integration of herbicides with diversified SOAs. Miller and Norsworthy (Reference Miller and Norsworthy2016) reported a lower density of Palmer amaranth with herbicide applications that involve multiple SOAs compared with a single herbicide SOA. Furthermore, repeated use of herbicides with the same SOA (e.g., 2,4-D or glufosinate) would select for the herbicide-resistant weed biotype. Resistance to 2,4-D has already been confirmed by Palmer amaranth in Kansas (Kumar et al. Reference Kumar, Liu, Boyer and Stahlman2019) and by a waterhemp biotype in Nebraska (Bernards et al. Reference Bernards, Crespo, Kruger, Gaussoin and Tranel2012). Therefore, a sequential and repeated application of 2,4-D to Enlist corn and soybean should be avoided.

The aboveground biomass of Palmer amaranth followed a similar trend to that of density (Table 4). The lowest (≤5 g m−2) Palmer amaranth biomass was recorded after acetochlor/clopyralid/mesotrione was applied compared with other preemergence-only and early postemergence–only herbicides at 30 d after early postemergence and 15 d after late postemergence. Palmer amaranth biomass at 30 d after early postemergence was greater after application of preemergence-only and early postemergence–only herbicides (i.e., acetochlor/clopyralid/flumetsulam, flufenacet/isoxaflutole/thiencarbazone-methyl, glyphosate/2,4-D, and 2,4-D). This might be due to the reduced efficacy of the applied residual herbicide and some Palmer amaranth plants being taller than 15 cm at the time early postemergence herbicides were applied.

At 15 d after late postemergence, acetochlor/clopyralid/mesotrione fb glufosinate, acetochlor/clopyralid/flumetsulam fb glufosinate, flufenacet/isoxaflutole/thiencarbazone-methyl fb glufosinate, acetochlor/clopyralid/mesotrione fb 2,4-D, and acetochlor/clopyralid/mesotrione reduced Palmer amaranth biomass to 2 to 4 g m−2 compared with a biomass of 143 g m−2 in the nontreated control group, accounting for ≥97% Palmer amaranth biomass reduction (Table 4). Shyam et al. (Reference Shyam, Chahal, Jhala and Jugulam2021b) reported 99% reduction in Palmer amaranth biomass with preemergence fb late postemergence herbicides applied to Enlist soybean. Sarangi and Jhala (Reference Sarangi and Jhala2019) reported ≥96% Palmer amaranth biomass reduction in soybean with preemergence fb late postemergence herbicide applications. Thus, applications of acetochlor/clopyralid/mesotrione fb 2,4-D, acetochlor/clopyralid/flumetsulam fb glufosinate, flufenacet/isoxaflutole/thiencarbazone-methyl fb glufosinate, and acetochlor/clopyralid/mesotrione resulted in 100% Palmer amaranth density reduction and ≥97% biomass reduction. Therefore, no seed production was observed after these treatments at the end of season (Table 5). To maintain the effectiveness of any herbicide program, however, it is crucial application timings be followed with appropriate crop and weed growth stages as described on the product label. For example, the 2,4-D label suggests applying the herbicide when broadleaf weeds are shorter than 15 cm (Anonymous 2022), therefore, if it is applied late, Palmer amaranth control can be compromised.

Table 5. Corn yield and Palmer amaranth seed production affected by herbicide programs in a 2,4-D–, glyphosate-, and glufosinate-resistant corn in field experiment conducted near Carleton, NE, in 2020 and 2021. a

a Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; NS, not significant; POST, postemergence.

b Year-by-treatment interaction for corn yield was significant; therefore, data are presented separately for both years.

c Means presented within each column with no common letters are significantly different according to the Tukey Kramer pairwise comparison test.

d Year-by-treatment interaction for Palmer amaranth seed production was nonsignificant; therefore, data were pooled across both years.

e Treatments with 0 Palmer amaranth seed production were excluded from the analysis.

f A priori orthogonal contrasts.

g P < 0.0001.

Corn Yield

Year-by-treatment interaction was significant; therefore, yield data are presented separately for both years (Table 5). Corn yield in 2020 was higher due to greater precipitation that provided sufficient moisture for better corn growth and development as it was a dryland field. Herbicide applications resulted in better grain yield in the range of 11,080 kg ha−1 to 12,910 kg ha−1 and 10,280 kg ha−1 to 12,420 kg ha−1, respectively, in 2020 and 2021 compared with 8,750 and 5,790 kg ha−1 yield from the untreated control. The lowest corn yield was obtained from the nontreated control, and was comparable to yields after applications of flufenacet/isoxaflutole/thiencarbazone-methyl, glyphosate/2,4-D, and 2,4-D. Orthogonal contrast analysis suggested that herbicides applied early postemergence only resulted in 10,850 kg ha−1 grain yield compared with 12,340 kg ha−1 after application of preemergence fb late postemergence herbicides. Similarly, Jones et al. (Reference Jones, Chandler, Morrison, Senseman and Tingle2001) concluded that preemergence fb late postemergence herbicide applications produced 8,890 to 9,570 kg ha−1 grain yield compared with glufosinate alone (8,300 kg ha−1) and the nontreated control (5,810 kg ha−1) in multiyear studies of 0glufosinate-resistant corn in Texas. Contrast analysis showed no difference in corn yield between preemergence fb late postemergence applications (11,730 to 12,340 kg ha−1) and preemergence-only applications (10,840 to 11,510 kg ha−1). Liu et al. (Reference Liu, Kumar, Jhala, Jha and Stahlman2021) observed no difference in corn yield with preemergence-only, preemergence fb early postemergence, and preemergence fb late postemergence herbicide applications, ranging from 9,210 to 10,215 kg ha−1.

Palmer Amaranth Seed Production

Year-by-treatment interaction for Palmer amaranth seed production was nonsignificant; therefore, data were pooled across both years (Table 5). The highest Palmer amaranth seed production (1,077,650 seed m−2) resulted from glufosinate applied alone compared with the nontreated control (939,690 seed m−2) (Table 5). Miranda et al. (Reference Miranda, Jhala, Bradshaw and Lawrence2021) reported that Palmer amaranth seed production per plant decreased as Palmer amaranth density increased, and concluded that the highest seed production (376,000 seed plant−1) occurred at the lowest density of 0.2 plants m–1 row, and that it declined by 12%, 28%, 55%, and 75% when density increased to 0.3, 0.5, 1, and 2 plants m–1 row, respectively. Palmer amaranth density in this study was 43 to 149 plants m–2 in the nontreated control compared with 0 to 15, 6 to 30, and 0 to 8 plants m–2 in preemergence-only, early postemergence–only, and preemergence fb late postemergence herbicide programs, respectively (Table 4). Therefore, lower seed production in the nontreated control compared with glufosinate applied early postemergence may have been caused by greater interplant competition in the nontreated control. Acetochlor/clopyralid/mesotrione applied preemergence without a follow-up late postemergence herbicide resulted in no Palmer amaranth seed production (Table 5) compared with flufenacet/isoxaflutole/thiencarbazone-methyl applied preemergence only and acetochlor/clopyralid/flumetsulam applied preemergence only, which produced about 0.5 million seed m−2. This might be due to acetochlor/clopyralid/mesotrione effectively reducing Palmer amaranth density and biomass compared with that of flufenacet/isoxaflutole/thiencarbazone-methyl and acetochlor/clopyralid/flumetsulam (Table 4), which resulted in no Palmer amaranth seed production.

Among the preemergence fb late postemergence herbicide programs, acetochlor/clopyralid/mesotrione fb 2,4-D, acetochlor/clopyralid/flumetsulam fb glufosinate, and flufenacet/isoxaflutole/ thiencarbazone-methyl fb glufosinate resulted in no Palmer amaranth seed production (Table 5). Flufenacet/isoxaflutole/thiencarbazone-methyl fb 2,4-D, acetochlor/clopyralid/mesotrione fb glufosinate, and acetochlor/clopyralid/flumetsulam fb 2,4-D resulted in Palmer amaranth seed production of 12,000 to 42,940 seed m−2 without difference among them. The contrast analysis showed that preemergence fb late postemergence herbicide programs had Palmer amaranth produced 14,050 seed m−2 compared with preemergence-only (325,490 seed m–2) and early postemergence–only (376,750 seed m–2) applications. Striegel and Jhala (Reference Striegel and Jhala2022) reported that Palmer amaranth seed production was 1,634 seed plant−1 with preemergence fb POST herbicide applications compared with 7,544 seed plant−1 with a postemergence-only herbicide. Similarly, Norsworthy et al. (Reference Norsworthy, Korres, Walsh and Powles2016) concluded that the inclusion of a preemergence herbicide with diversified SOA fb glufosinate/glyphosate resulted in ≥97% reduction in Palmer amaranth seed production compared to a glyphosate-only treatment.

Practical Implications

Results of this study indicated that preemergence fb late postemergence and preemergence-only herbicide regimens are available for season-long Palmer amaranth control and reduce seed production in Enlist corn. Based on contrast analysis, Palmer amaranth seed production was reduced to 14,050 seed m–2, and corn yield of 12,340 and 11,730 kg ha−1 was obtained after preemergence fb late postemergence herbicide applications compared with 325,490 seed m–2 and grain yield of 10,840 and 11,510 kg ha−1 in preemergence-only and 376,750 seed m–2 and 10,850 and 10,030 kg ha−1 in early postemergence–only herbicide programs, respectively, in 2020 and 2021. Enlist technology provides an option for growers with a long window and the flexibility for postemergence application of 2,4-D choline (Enlist ONE) for management of herbicide-resistant Palmer amaranth until the V8 growth stage or a height of 76 cm, or even more than this stage of Enlist corn with precautionary measures. For instance, if corn is taller than 76 cm, 2,4-D choline should be applied using drop nozzles aligned so that spraying does not reach into the whorl of Enlist corn plants (Anonymous 2022). Enlist corn adoption will likely be higher in the future due to resistance to aryloxyphenoxypropionates, which allow the use of quizalofop-p-ethyl on Enlist corn for controlling glyphosate/glufosinate-resistant volunteer corn (Striegel et al. Reference Striegel, Lawrence, Knezevic, Krumm, Hein and Jhala2020). This is particularly important in states such as Nebraska, where continuous corn production is common. Metabolic resistance in the Palmer amaranth biotype from Kansas, which is resistant to six commonly used corn herbicides, is challenging for corn growers (Shyam et al. Reference Shyam, Borgato, Peterson, Dille and Jugulam2021a). Therefore, apart from using Enlist corn technology and herbicides with diversified SOAs, there is a need to integrate best management practices with cultural and nonchemical approaches such as scouting of fields before and after herbicide application, row width manipulation, cover cropping, diverse crop rotations, weed seed destruction for persistent control of MHR Palmer amaranth, and reducing seedbank additions. For instance, Price et al. (Reference Price, Balkcom, Duzy and Kelton2012) reported that a high-residue cereal cover crop in combination with broadcast preemergence herbicide was important for managing MHR Amaranthus species.

Acknowledgments

We thank Irvin Schleufer, Jasmine Mausbach, Trey Stephens, Mandeep Singh, Will Neels, and Shawn McDonald for their assistance with the project. We thank the associate editor and reviewers for their comments and edits to improve quality of this manuscript.

Funding

This project was supported with funding from the Nebraska Corn Board and Bayer Crop Science.

Competing Interests

The authors declare none.

Footnotes

Associate Editor: Aaron Hager, University of Illinois

References

Anonymous (2017) Liberty herbicide product label. EPA Reg. No. 264-829. Research Triangle Park, NC: Bayer Crop Science. 29 pGoogle Scholar
Anonymous (2022) Enlist ONE herbicide product label. EPA Reg. No. 62719-695. Indianapolis, IN: Corteva agriscience. 2 pGoogle Scholar
Aulakh, JS, Jhala, AJ (2015) Comparison of glufosinate-based herbicide programs for broad-spectrum weed control in glufosinate-resistant soybean. Weed Technol 29:419430 CrossRefGoogle Scholar
Bagavathiannan, MV, Norsworthy, JK (2012) Late-season seed production in arable weed communities: management implications. Weed Sci 60:325334 CrossRefGoogle Scholar
Barnett, KA, Culpepper, SA, York, AC, Steckel, LE (2013) Palmer amaranth control by glufosinate plus flometuron applied post emergence to WideStrike cotton. Weed Technol 27:291297 CrossRefGoogle Scholar
Bensch, CN, Horak, MJ, Peterson, D (2003) Interference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Sci 51:3743 CrossRefGoogle Scholar
Bernards, M, Crespo, R, Kruger, G, Gaussoin, R, Tranel, P (2012) A waterhemp (Amaranthus tuberculatus) population resistant to 2,4-D Weed Sci 60:379384 CrossRefGoogle Scholar
Brabham, C, Norsworthy, JK, Houston, MM, Varanasi, VK, Barber, T (2019) Confirmation of S-metolachlor resistance in Palmer amaranth (Amaranthus palmeri). Weed Technol 33:720726 CrossRefGoogle Scholar
Chahal, PS, Aulakh, J, Mithila, J, Jhala, AJ (2015) Herbicide-resistant Palmer amaranth (Amaranthus palmeri S. Wats) in the United States: impact, mechanism of resistance, and management. Pages 1–40 in Price AJ, Kelton JA, Sarunaite L, eds. Herbicides, Agronomic Crops, and Weed Biology. New York: Tech Scientific PublisherCrossRefGoogle Scholar
Chahal, PS, Barnes, ER, Jhala, AJ (2021) Emergence pattern of Palmer amaranth (Amaranthus palmeri) influenced by tillage timings and residual herbicides. Weed Technol 35:433439 CrossRefGoogle Scholar
Chahal, PS, Ganie, ZA, Jhala, AJ (2018a) 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. Front Plant Sci 8:111 CrossRefGoogle Scholar
Chahal, PS, Irmak, S, Jugulam, M, Jhala, AJ (2018b) Evaluating effect of degree of water stress on growth and fecundity of Palmer amaranth (Amaranthus palmeri) using soil moisture sensors. Weed Sci 66:738745 CrossRefGoogle Scholar
Chahal, PS, Jhala, AJ (2015) Herbicide programs for control of glyphosate resistant volunteer corn in glufosinate-resistant soybean. Weed Technol 29:431443 CrossRefGoogle Scholar
Chahal, PS, Varanasi, VK, Jugulam, M, Jhala, AJ (2017) Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in Nebraska: confirmation, EPSPS gene amplification, and response to POST corn and soybean herbicides. Weed Technol 31:8093 CrossRefGoogle Scholar
Foster, D, Steckel, L (2022) Confirmation of dicamba-resistant Palmer amaranth in Tennessee. Weed Technol 36:777780 CrossRefGoogle Scholar
Garetson, R, Singh, V, Singh, S, Dotray, P, Bagavathiannan, M (2019) Distribution of herbicide-resistant Palmer amaranth (Amaranthus palmeri) in row crop production systems in Texas. Weed Technol 33:355365 CrossRefGoogle Scholar
Heap, I (2024) The International Herbicide-Resistant Weed Database. https://www.weedscience.org/Pages/SpeciesbySOATable.aspx. Accessed: March 15, 2024Google Scholar
Jha, P, Norsworthy, JK (2009) Soybean canopy and tillage effects on emergence of Palmer amaranth (Amaranthus palmeri) from a natural seed bank. Weed Sci 57:644651 CrossRefGoogle Scholar
Jhala, AJ, Malik, MS, Willis, JB (2015) Weed control and crop tolerance of micro-encapsulated acetochlor applied sequentially in glyphosate-resistant soybean. Can J Plant Sci 95:973981 CrossRefGoogle Scholar
Jhala, AJ, Norsworthy, JK, Ganie, ZA, Sosnoskie, LM, Beckie, HJ, Mallory-Smith, CA, Liu, J, Wei, W, Wang, J, Stoltenberg, DE (2021) Pollen-mediated gene flow and transfer of resistance alleles from herbicide-resistant broadleaf weeds. Weed Technol 35:173187 CrossRefGoogle Scholar
Jhala, AJ, Sandell, LD, Rana, N, Kruger, GR, Knezevic, SZ (2014) Confirmation and control of triazine and 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide-resistant Palmer amaranth (Amaranthus palmeri) in Nebraska. Weed Technol 28:2838 CrossRefGoogle Scholar
Jhala, AJ, Sandell, LD, Sarangi, D, Kruger, GR, Knezevic, SZ (2017) Control of glyphosate-resistant common waterhemp (Amaranthus rudis) in glufosinate resistant soybean. Weed Technol 31:3245 CrossRefGoogle Scholar
Johnson, G, Breitenbach, F, Behnken, L, Miller, R, Hoverstad, T, Gunsolus, J (2012) Comparison of herbicide tactics to minimize species shifts and selection pressure in glyphosate-resistant soybean. Weed Technol 26:189194 CrossRefGoogle Scholar
Jones, C, Chandler, J, Morrison, J, Senseman, S, Tingle, C (2001) Glufosinate combinations and row spacing for weed control in glufosinate-resistant corn (Zea mays). Weed Technol 15:141147 CrossRefGoogle Scholar
Klingaman, TE, Oliver, LR (1994) Palmer amaranth (Amaranthus palmeri) interference in soybeans (Glycine max). Weed Sci 42:523527 CrossRefGoogle Scholar
Kohrt, JR, Sprague, CL, Nadakuduti, SS, Douches, D (2016) Confirmation of a three-way (glyphosate, ALS, and atrazine) herbicide-resistant population of Palmer amaranth (Amaranthus palmeri) in Michigan. Weed Sci 65:327338 CrossRefGoogle Scholar
Kumar, V, Liu, R, Boyer, G, Stahlman, PW (2019) Confirmation of 2,4-D resistance and identification of multiple resistance in a Kansas Palmer amaranth (Amaranthus palmeri) population. Pest Manag Sci 75:29252933 CrossRefGoogle Scholar
Kumar, V, Liu, R, Stahlman, PW (2020) Differential sensitivity of Kansas Palmer amaranth populations to multiple herbicides. Agron J 112:21522163 CrossRefGoogle Scholar
Liu, R, Kumar, V, Jha, P, Stahlman, PW (2022) Emergence pattern and periodicity of Palmer amaranth (Amaranthus palmeri) populations from southcentral Great Plains. Weed Technol 36:110117 CrossRefGoogle Scholar
Liu, R, Kumar, V, Jhala, A, Jha, P, Stahlman, PW (2021) Control of glyphosate- and mesotrione-resistant Palmer amaranth in glyphosate-and glufosinate-resistant corn. Agron J 113:53625372 CrossRefGoogle Scholar
Massinga, RA, Currie, RS, Horak, MJ, Boyer, J Jr (2001) Interference of Palmer amaranth in corn. Weed Sci 49:202208 CrossRefGoogle Scholar
Mausbach, J, Irmak, S, Sarangi, D, Lindquist, J, Jhala, AJ (2021) Control of acetolactate synthase inhibitor/glyphosate resistant Palmer amaranth (Amaranthus palmeri) in isoxaflutole/glufosinate/glyphosate-resistant soybean. Weed Technol 35:779785 CrossRefGoogle Scholar
McDonald, S, Sarangi, D, Rees, J, Jhala, A (2023) A follow-up survey to assess stakeholders’ perspectives on weed management challenges and current practices in Nebraska, USA. Agrosyst Geosci Environ 6. https://www.doi.org/10.1002/agg2.20425 CrossRefGoogle Scholar
Meyer, CJ, Norsworthy, JK, Young, BG, Steckel, LE, Bradley, KW, Johnson, WG, Loux, MM, Davis, VM, Kruger, GR, Bararpour, MT, Ikley, JT, Spaunhorst, DJ, Butts, TR (2015) Herbicide program approaches for managing glyphosate resistant Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus and Amaranthus rudis) in future soybean-trait technologies. Weed Technol 29:716729 CrossRefGoogle Scholar
Miller, MR, Norsworthy, JK (2016) Evaluation of herbicide programs for use in a 2,4-D–resistant soybean technology for control of glyphosate-resistant Palmer amaranth (Amaranthus palmeri). Weed Technol 30:366376 CrossRefGoogle Scholar
Miranda, J, Jhala, A, Bradshaw, J, Lawrence, N (2021) Palmer amaranth (Amaranthus palmeri) interference and seed production in dry edible bean. Weed Technol 35:9951006 CrossRefGoogle Scholar
Norsworthy, JK, Korres, NE, Walsh, MJ, Powles, SB (2016) Integrating herbicide programs with harvest weed seed control and other fall management practices for the control of glyphosate-resistant Palmer amaranth (Amaranthus palmeri). Weed Sci 64:540550 CrossRefGoogle Scholar
Oliveira, MC, Jhala, AJ, Bernards, ML, Proctor, CA, Stepanovic, S, Werle, R (2022) Palmer amaranth (Amaranthus palmeri) adaptation to US Midwest agroecosystems. Front Agron 4:887629. https://doi.org/10.3389/fagro.2022.887629 CrossRefGoogle Scholar
Price, AJ, Balkcom, KS, Duzy, LM, Kelton, JA (2012) Herbicide and cover crop residue integration for Amaranthus control in conservation agriculture cotton and implications for resistance management. Weed Technol 26:490498 CrossRefGoogle Scholar
Priess, GL, Norsworthy, JK, Godara, N, Mauromoustakos, A, Butts, TR, Roberts, TL, Barber, T (2022) Confirmation of glufosinate-resistant Palmer amaranth and response to other herbicides. Weed Technol 36:368372 CrossRefGoogle Scholar
Sarangi, D, Jhala, AJ (2019) Palmer amaranth (Amaranthus palmeri) and velvetleaf (Abutilon theophrasti) control in no-tillage conventional (non-genetically engineered) soybean using overlapping residual herbicide programs. Weed Technol 33:95105 CrossRefGoogle Scholar
Sarangi, D, Sandell, LD, Kruger, GR, Knezevic, SZ, Irmak, S, Jhala, AJ (2017) Comparison of herbicide programs for season-long control of glyphosate resistant common waterhemp (Amaranthus rudis) in soybean. Weed Technol 31:5366 CrossRefGoogle Scholar
Shyam, C, Borgato, EA, Peterson, DE, Dille, JA, Jugulam, M (2021a) Predominance of metabolic resistance in a six-way-resistant Palmer amaranth (Amaranthus palmeri) population. Front Plant Sci 11:614618 CrossRefGoogle Scholar
Shyam, C, Chahal, PS, Jhala, AJ, Jugulam, M (2021b) Management of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in 2,4-D choline, glufosinate, and glyphosate-resistant soybean. Weed Technol 35:136143 CrossRefGoogle Scholar
Sosnoskie, LM, Webster, TM, Grey, TL, Culpepper, AS (2014) Severed stems of Amaranthus palmeri are capable of regrowth and seed production in Gossypium hirsutum . Ann Appl Biol 165:147154 CrossRefGoogle Scholar
Steckel, GJ, Wax, LM, Simmons, FW, Phillips, WH II (1997) Glufosinate efficacy on annual weeds is influenced by rate and growth stage. Weed Technol 11:484488 CrossRefGoogle Scholar
Striegel, A, Jhala, AJ (2022) Economics of reducing Palmer amaranth seed production in dicamba/glufosinate/glyphosate-resistant soybean. Agron J 114:25182540 CrossRefGoogle Scholar
Striegel, A, Lawrence, NC, Knezevic, SZ, Krumm, JT, Hein, G, Jhala, AJ (2020) Control of glyphosate/glufosinate-resistant volunteer corn in corn resistant to aryloxyphenoxypropionates. Weed Technol 34:309317 CrossRefGoogle Scholar
Van Wychen, L (2022) Survey of the most common and troublesome weeds in broadleaf crops, fruits & vegetables in the United States and Canada. Weed Science Society of America National Weed Survey Dataset. https://wssa.net/wp-content/uploads/2022-Weed-Survey-Broadleaf-crops.xlsx. Accessed: September 1, 2023Google Scholar
Vencill, WK, Grey, TL, Culpepper, AS, Gaines, C, Westra, P (2008) Herbicide-resistance in the Amaranthaceae. J Plant Dis Prot 21:4144 Google Scholar
Ward, SM, Webster, TM, Steckel, LE (2013) Palmer amaranth (Amaranthus palmeri): a review. Weed Technol 27:1227 CrossRefGoogle Scholar
Wiggins, MS, McClure, MA, Hayes, RM, Steckel, LE (2015) Integrating cover crops and post herbicides for glyphosate-resistant Palmer amaranth (Amaranthus palmeri) control in corn. Weed Technol 29:412418 CrossRefGoogle Scholar
Figure 0

Table 1. Monthly mean air temperature and total precipitation during the 2020 and 2021 growing seasons along with the 30-yr average at the experiment site near Carleton, NE.a

Figure 1

Table 2. Herbicides, application timings, and rates used for control of acetolactate synthase inhibitor/atrazine/glyphosate–resistant Palmer amaranth in a 2,4-D/glufosinate/glyphosate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021.

Figure 2

Table 3. Control of multiple herbicide–resistant Palmer amaranth affected by herbicide programs in a 2,4-D/glufosinate/glyphosate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021.a

Figure 3

Table 4. Multiple herbicide–resistant Palmer amaranth density and above-ground biomass as affected by the herbicide programs in a 2,4-D/glyphosate/glufosinate–resistant corn in field experiments conducted near Carleton, NE, in 2020 and 2021.a,b

Figure 4

Table 5. Corn yield and Palmer amaranth seed production affected by herbicide programs in a 2,4-D–, glyphosate-, and glufosinate-resistant corn in field experiment conducted near Carleton, NE, in 2020 and 2021.a