Impact of irrigation levels on herbicide activity in the cotton production system

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.

Foliar fertilizers have become one of the many inputs used in cotton (Gossypium hirsutum L) production systems across the U.S. Cotton Belt. Their usefulness, however, in producing high yielding, high quality cotton remains to be resolved This study was conducted to determine the effects of foliar fertilizers on cotton: (i) lint and seed yields, (ii) plant dry weight, (iii) plant leaf area, and (iv) leaf nitrogen concentration. During the 1990 growing season, this study was conducted at the Texas Tech University Research Farm east of New Deal, TX, on a Pullman clay loam (fine, mixed, thermic, Torrertic Paleustoll). Six foliar treatments were incorporated into a randomized complete block design with six blocks. Treatments 2 (15-2-0 with Ca), 3 (8-32-5 with micronutrients), and 4 (8-8-8 with micronutrients) were commercial products and were applied in compliance with their manufacturers' recommendations. Treatments 5 and 6 (46-0-0) were applied at various rates. During the 1991 growing season, this study was conducted at an on-farm location northeast of Petersburg, TX. The soil at this location was also a Pullman clay loam. The same six foliar treatments were incorporated into a randomized complete block design with four blocks. Foliar treatments were applied during both growing seasons at 0, 2, 4, 6, and 8 wk after matchead square. One week after each treatment application, 10 plants were removed from each plot and divided into three nodal horizons: (i) from node 6 to node 9, (ii) from node 10 to node 13, and (iii) node 14 and above. Leaf total and nitrate N concentrations were determined by these nodal horizons. Also, at 1, 5, and 9 wk after matchead square, plant leaf areas and dry weights were determined. Lint yields were determined after a killing freeze in 1990 and after crop termination in 1991. Feed grade urea increased leaf total N concentrations during 1990, but these results were not repeated in 1991. Urea also increased leaf nitrate N during both growing seasons. However, plant leaf area and dry weight, and lint and seed yields were not significantly affected by foliar fertilizers. Cost-benefit analyses were not conducted due to the lack of a significant yield response from foliar fertilizers. We conclude none of the costs associated with foliar fertilization will be recovered in net returns.

ABSTRACT: The emergence of resistant biotypes of the Amaranthus palmeri species in cotton production areas of the state of Mato Grosso, Brazil, generated the need for correct identification of this species and information on viable herbicidal tools for their management. Thus, greenhouse experiments were conducted to evaluate the efficacy of alternative herbicides applied to A. palmeri in pre and post emergence. A randomized block design with four replications was used. The efficacy of herbicides applied in pre emergence was evaluate in two experiments, one in a clayey and other in a sandy soil; 9 herbicide treatments (8 with herbicide application and a control without application) were applied on each soil. Subsequently, two experiments with different populations of A. palmeri were conducted, using a 13 x 2 factorial arrangement, to evaluate the efficacy of herbicides applied in post emergence. The factors consisted of 13 herbicide treatments (12 with herbicide application and a control without application) and two weed development stages (2-4 and 6-8 leaves). Pre-emergence application of the flumioxazin, S-metolachlor, isoxaflutole, and trifluralin herbicides controlled the weed satisfactorily in both evaluated soils. The sulfentrazone and metribuzin herbicides were effective in the sandy soil, and diuron was effective in the clayey soil. The clomazone herbicide did not successfully controlled the A. palmeri plants in any of the soils. All post-emergence herbicide treatments were effective for the management of A. palmeri plants, when they were applied at the 2-4 leaf stage.

Palmer amaranth is a relatively recent arrival in Western Nebraska, where acetolactate synthase (ALS)-inhibitor-resistant biotypes are common in the region. With limited effective postemergence (POST) herbicides for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean, a sequential preemergence (PRE) followed by (fb) POST program of very long-chain fatty acid (VLCFA)-inhibiting herbicides shows promise. Currently, dimethenamid-P is the only VLCFA-inhibiting herbicide registered for POST use in dry edible bean in Nebraska. The objective of this study was to assess the crop safety and effectiveness in weed control of sequential PRE fb POST programs, including pendimethalin + dimethenamid-P applied PRE fb dimethenamid-P POST, pendimethalin + S-metolachlor PRE fb S-metolachlor POST, and pendimethalin + pyroxasulfone PRE fb POST, in comparison with pendimethalin + dimethenamid-P applied PRE fb imazamox + bentazon + fomesafen applied POST in dry edible bean. Results showed that sequential PRE fb POST programs were more effective in reducing both the density and biomass of Palmer amaranth compared to PRE-alone programs. Pendimethalin + dimethenamid-P applied PRE fb dimethenamid-P POST, along with pendimethalin + S-metolachlor PRE fb S-metolachlor POST, resulted in over 85% control of Palmer amaranth, similar to the effectiveness of pendimethalin + dimethenamid-P PRE fb fomesafen + imazamox + bentazon applied POST. Pendimethalin + pyroxasulfone applied PRE-alone and the application of pendimethalin + pyroxasulfone PRE fb pyroxasulfone POST showed inconsistent control of Palmer amaranth, causing high crop injury, stand loss, and delayed maturity, ultimately leading to yield loss. Dimethenamid-P and S-metolachlor demonstrated excellent crop safety when applied either PRE-only or sequentially. Pendimethalin + S-metolachlor PRE fb S-metolachlor POST provided control of Palmer amaranth comparable to that achieved with POST applications of dimethenamid-P and imazamox + bentazon + fomesafen.

Palmer amaranth (Amaranthus palmeri S. Wats.) invasion negatively impacts cotton (Gossypium hirsutum L.) production systems throughout the United States. The objective of this study was to evaluate canopy hyperspectral narrowband data as input into the random forest machine learning algorithm to distinguish Palmer amaranth from cotton. The study focused on differentiating the Palmer amaranth from cotton near-isogenic lines with bronze, green, and yellow leaves. A spectroradiometer was used to acquire hyperspectral reflectance measurements of Palmer amaranth and cotton canopies for two separate dates, December 12, 2016, and May 14, 2017. Data were collected from plants that were grown in a greenhouse. The spectral data were aggregated to twenty-four hyperspectral narrowbands proposed for study of vegetation and agriculture crops. Those bands were tested by the conditional inference version of random forest (cforest) to differentiate the Palmer amaranth from cotton. Classifications were binary: Palmer amaranth and cotton bronze, Palmer amaranth and cotton green, and Palmer amaranth and cotton yellow. Classification accuracies were verified with overall, user’s, and producer’s accuracy. For the two dates combined, overall accuracy ranged from 77.8% to 88.9%. The highest overall accuracies were observed for the Palmer amaranth versus the cotton yellow classification (88.9%, December 12, 2016; 83.3%, May 14, 2017). Producer’s and user’s accuracies range was 66.7% to 94.4%. Errors were predominately attributed to cotton being misclassified as Palmer amaranth. The overall results indicated that cforest has moderate to strong potential for differentiating Palmer amaranth from cotton when it used hyperspectral narrowbands known to be useful for vegetation and agricultural surveys as input variables. This research further supports using hyperspectral narrowband data and cforest as decision support tools in cotton production systems.

Glyphosate‐ and acetolactate synthase (ALS)‐resistant Palmer amaranth (Amaranthus palmeri S. Wats.) has become the most common and troublesome weed in multiple crops in the southeast United States. Pyroxasulfone inhibits biosynthesis of very long chain fatty acids (VLCFAs) and can provide soil residual weed control. However, there has been little information about pyroxasulfone for control of weeds in the southeastern United States. Experiments were conducted in 2010 and 2011 in fields infested with multiple weeds including glyphosate‐ and ALS‐resistant Palmer amaranth to compare herbicides with different modes of action. These included pyroxasulfone, a VLCFA inhibitor, S‐metolachlor (a VLCFA inhibitor), flumioxazin, a protoporphyinogen oxidase (PROTOX) inhibitor, metribuzin, a photosystem II inhibitor, fomesafen (a PROTOX inhibitor), and glyphosate, an enolpyruvylshikimate 3‐phosate synthase inhibitor. Soybean [Glycine max (L.) Merr.] (Asgrow DP7870 RR in 2010 and Asgrow AG6931 in 2011) were conventionally planted and evaluated for injury, stand density, and yields. Weed control was based on evaluation of glyphosate‐ and ALS‐resistant Palmer amaranth, sicklepod [Senna obtusifolia (L.) H.S.Irwin & Barneby], Florida beggarweed [Desmodium tortuosum (Sw.) DC.], smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.], and wild poinsettia (Euphorbia heterophylla L.). There were no effects on soybean emergence for any preemergence (PRE) herbicide treatment. There was no significant soybean injury with pyroxasulfone at rates of 0.86 to 2.57 oz a.i./acre for PRE or early postemergence (EPOST) application. For season‐long residual control of glyphosate‐ and ALS‐resistant Palmer amaranth, pyroxasulfone at 1.28 oz a.i./acre and greater were required for 87% and greater control. Pyroxasulfone plus flumioxazin at 1.50 and 1.01 oz a.i./acre PRE, respectively, provided season‐long Palmer amaranth control at 99%. Pyroxasulfone also controlled Florida beggarweed and smallflower morningglory. A combination of PRE, EPOST, and postemergence (POST) herbicide applications (glyphosate or fomesafen) were required for sicklepod and wild poinsettia control. Maximum yields required the combination of residual PRE and contact and residual EPOST herbicide applications. Successful soybean production in the southeast United States will require crop rotation and use of multiple herbicide modes of action PRE, EPOST, and POST to minimize herbicide resistant Palmer amaranth related issues.

Biotypes of Palmer amaranth that are resistant to acetolactate synthase (ALS) inhibitor are becoming widespread in western Nebraska. There are limited effective postemergence (POST) herbicides labeled for ALS-inhibitor-resistant Palmer amaranth control in dry edible bean. The objective of this study was to evaluate the efficacy of dimethenamid-Pin a sequential preemergence (PRE) fb followed by (fb) POST program at two POST application timings, the first and third trifoliate stages (V1 and V3, respectively), for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean. A field study was conducted in 2019, 2020, and 2021 in Scottsbluff, NE. PRE-alone applications of pendimethalin + dimethenamid-Pprovided inconsistent Palmer amaranth control. Dimethenamid-Papplied POST following a PRE application of pendimethalin + dimethenamid-Pprovided effective (>90%) Palmer amaranth control at 4 wk after V3 only at the V1 application timing in 2019. In 2020 and 2021 dimethenamid-Papplied POST at V1 and V3 following a PRE application of pendimethalin + dimethenamid-Pprovided 99% and 98% Palmer amaranth control at 4 wk after V3, and 98% and 94% Palmer amaranth control at harvest, respectively. Palmer amaranth biomass was reduced by 95% to 99% and by 96% to 98% compared with the -nontreated control when dimethenamid-Pwas applied POST at V1 and V3, respectively, following a PRE application of pendimethalin + dimethenamid-Pin 2020 and 2021. Application of a mixture of dimethenamid-Pwith imazamox + bentazon POST provided similar results to those of the fomesafen-containing treatments and dimethenamid-Palone POST. Dimethenamid-Papplied POST following a PRE application of pendimethalin + dimethenamid-Presulted in similar yield as the fomesafen-containing treatments. If fomesafen is not an option due to the crop rotation interval restriction, using dimethenamid-Pin a sequential PRE fb POST program is the only effective alternative to control ALS-inhibitor–resistant Palmer amaranth in Nebraska. The use of dimethenamid-Pin a sequential PRE fb POST program, alone or mixed with foliar-active herbicides should be considered by dry edible bean growers who are dealing with ALS-inhibitor-resistant Palmer amaranth.

Glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) is a widespread problem in cotton (Gossypium hirsutum L.) production. Growers are encouraged to include residual herbicides applied preemergence (PRE) and postemergence (POST) in their management systems to control this weed adequately. Pyroxasulfone, an isoxazoline herbicide with the same mode of action as acetochlor and S-metolachlor, effectively controls Palmer amaranth in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The objective of this study was to compare cotton tolerance and Palmer amaranth control with pyroxasulfone, acetochlor, and S-metolachlor applied PRE and POST to cotton. Treatments in a field study at four locations included pyroxasulfone at 60, 90, and 120 g a.i. ha-1 applied PRE or mixed with glyphosate and applied POST; an encapsulated formulation of acetochlor at 1260 g a.i. ha-1 applied PRE or POST with glyphosate; and S-metolachlor at 1070 g a.i. ha-1 applied POST with glyphosate. Pyroxasulfone PRE increased late-season Palmer amaranth control 14 to 27% and increased yield in one of two years. Similar results were observed with pyroxasulfone and acetochlor applied PRE. Pyroxasulfone, acetochlor, and S-metolachlor applied POST with glyphosate did not increase Palmer amaranth control compared with glyphosate alone. Cotton was less tolerant of pyroxasulfone applied PRE or POST than acetochlor applied PRE or POST or S-metolachlor applied POST. Cotton growth was reduced 14 to 17% by pyroxasulfone applied PRE and stand was reduced 10 to 25%. Acetochlor PRE reduced cotton growth 6% but did not affect stand. Pyroxasulfone applied POST caused 23 to 36% necrosis 7 d after application and reduced cotton growth 21 to 39% at 14 d after application compared with 6 to 17% necrosis and 3 to 8% growth reduction caused by acetochlor and S-metolachlor. Yields were not reduced by any treatment.

Palmer amaranth (Amaranthus palmeri S. Wats.) is a major weed problem of cotton (Gossypium hirsutum L.) production systems in the southern United States. Hyperspectral remote sensing has shown promise as a tool for crop weed discrimination, and there is a growing interest in using this technology for identifying weeds in cotton production systems. Information is lacking on differentiating Palmer amaranth from cotton with an okra leaf structure based on canopy hyperspectral reflectance properties. Two greenhouse studies were conducted to compare canopy hyperspectral reflectance profiles of Palmer amaranth to canopy hyperspectral reflectance profiles of okra and super-okra leaf cotton and to identify optimal regions of the electromagnetic spectrum for their discrimination. Ground-based hyperspectral measurements of the plant canopies were obtained with a spectroradiometer (400 - 2350 nm range). Analysis of variance (ANOVA, p ≤ 0.05), Dunnett’s test (p ≤ 0.05), and difference and sensitivity measurements were tabulated to determine the optimal wavebands for Palmer amaranth and cotton discrimination. Results were inconsistent for Palmer amaranth and okra leaf cotton separation. Optimal wavebands for distinguishing Palmer amaranth from super-okra leaf cotton were observed in the shortwave infrared region (2000 nm and 2180 nm) of the optical spectrum. Ground-based and airborne sensors can be tuned into the shortwave infrared bands identified in this study, facilitating application of remote sensing technology for Palmer amaranth discrimination from super-okra leaf cotton and implementation of the technology as a decision support tool in cotton weed management programs.

Separate field experiments were conducted in central and southeast Missouri during 2009 and 2010 to evaluate the effect of preemergence (PRE) and postemergence (POST) herbicide programs on Palmer amaranth ( Amaranthus palmeri S. Wats.) and waterhemp ( Amaranthus rudis Sauer) control, soybean [ Glycine max (L.) Merr.] yield, and net income in conventional, glyphosate‐resistant, and glufosinate‐resistant soybean production systems. Visual control evaluations 10 wk after emergence at the waterhemp site revealed that all preemergence only applications (PRE‐only) and preemergence followed by a postemergence applications (PRE fb POST) provided greater than 92% waterhemp control in either soybean system and at the Palmer amaranth site and all PRE‐only provided greater than 83% Palmer amaranth control across soybean systems. Averaged across all herbicide programs at both locations, glufosinate‐resistant soybean provided the highest grain yield and net return followed by glyphosate‐resistant and conventional soybean systems. Furthermore, with the exception of the conventional PRE‐only program at the waterhemp site, all glyphosate‐resistant soybean herbicide programs provided greater net return than all conventional herbicide programs. Collectively, the results from both trials indicate that programs containing PRE herbicide treatments provide the best opportunity for season‐long control of waterhemp and Palmer amaranth and highest grain yields and net returns in conventional, glyphosate‐resistant, or glufosinate‐resistant soybean systems. The results from these experiments also suggest that Palmer amaranth may be particularly difficult to control in conventional soybean systems.

Southernpea is a major vegetable crop in Arkansas and Oklahoma for commercial production and home gardens. Complete weed control is necessary for this crop in commercial production to keep the peas free of contaminants and achieve high harvest efficiency. Several weeds like pigweed, cocklebur, velvetleaf, lambsquarters, hophornbeam copperleaf, nightshade, nutsedge, and morninglories are difficult to control in this crop because of limited herbicide options. Sandea (halosulfuron) is an excellent herbicide for nutsedge control and has activity on most of the weeds mentioned above. It has both soil and foliar activity. Sandea is labeled for several vegetable crops and southernpea may have enough tolerance to Sandea to warrant a label expansion. Experiments were conducted in Arkansas and Oklahoma between 2002 and 2005 to determine the tolerance of southernpea to Sandea and its efficacy on some weed species. In Oklahoma, trials were conducted in LeFlore County and at the Bixby Research Station in 2002 and 2003. Treatments consisted of various herbicides applied preemergence (PRE) or postemergence (POST), among which were some Sandea treatments. The doses of Sandea tested ranged from 0.024 to 0.048 lb a.i./A with some treatments applied with Basagran (bentazon), POST. Preemergence treatments were applied at 20 GPA and POST treatments at 30 GPA. Experimental units were arranged in randomized complete block design with four replications. The cultivar used was Early Scarlet. Plots were comprised of four rows, spaced either 30 or 36 inches, depending on location, 15 ft long. The crop at Bixby was irrigated, but not at LeFlore. In Arkansas, two experiments were conducted in 2005 at the Vegetable Station in Kibler. One experiment was setup in a split-plot design, with four replications, with cultivar as mainplot and Sandea treatments as subplot. Eleven advanced breeding lines and Early Scarlet were used. Four Sandea treatments, using doses of 0.048 and .096 lb ai/A applied either PRE, at 1 to 2-trifoliate (early POST), and at 3- to 4-trifoliate (late POST) were tested. The second experiment compared the responses of 16 advanced breeding lines and Early Scarlet to 0.096 lb a.i./A Sandea applied PRE. Plot size at Kibler consisted of 4 rows, spaced 36 inches, 20 ft long. Herbicide treatments were applied at 20 GPA spray volume and the crop was sprinkler irrigated as needed. In Oklahoma, the commercial rate of Sandea (0.032 to 0.048 lb a.i.) did not cause any injury to southernpea when applied PRE regardless of availability of irrigation. However, when applied POST, significant stunting (up to about 20%) of plants was observed in both locations. This level of injury did not cause significant yield loss. The trial at Bixby could not be harvested due to excessive pigweed biomass later in the season. Sandea controlled Palmer amaranth and carpetweed >90% when applied PRE, but had no activity on these species when applied POST. Conversely, Sandea had excellent activity (100%) on common cocklebur when applied POST, but ineffective when applied PRE. Trials in Arkansas were strictly for tolerance evaluation so no weed control data was collected. In Arkansas, the PRE timing was also safer than POST when 0.096 lb ai Sandea was used. The 11 advanced lines tested in trial 1 were among the top 15 lines selected for tolerance to Sandea from a preliminary screen. These selected lines still showed different levels of tolerance to high rates of Sandea, but may not show any difference among each other at the recommended rates. The best lines were 00-609 and 00-178, which showed no yield reduction when treated with 0.096 lb ai Sandea PRE. All advanced lines had higher yield than Early Scarlet without herbicide treatment. In trial 2, 01-103, 01-180, and 01-181 had 0% to 10% yield loss when treated with 0.096 lb ai Sandea, PRE. All three had similar or greater yield than Early Scarlet. The commercial standard incurred about 20% to 30% yield loss from the high dose of Sandea applied PRE in both trials in Arkansas. Sandea is safe for cowpea, PRE at recommended doses. However, some advanced lines can tolerate high rates of Sandea. Some weeds are controlled by Sandea PRE, but not POST and vice versa.

Field experiments were conducted from 1999 to 2001 to evaluate preemergence (PRE) activity of cloransulam on broadleaf weed species and to determine the effectiveness of cloransulam as a PRE herbicide in glyphosate-resistant soybean weed management systems. Cloransulam PRE controlled prickly sida, velvetleaf, and morningglory species even at reduced rates (recommended rate 36 g ai/ha) but only suppressed growth of Palmer amaranth, hemp sesbania, and sicklepod. Cloransulam applied PRE provided initial control or suppression of most weeds, but late-season control declined appreciably. Adding metribuzin to cloransulam PRE generally improved control of hemp sesbania, Palmer amaranth, annual grasses, and morningglory species, leading to soybean yield increases. Control of weeds was greater on a silt loam soil compared with a silty clay soil. Delayed herbicide activation by rainfall or irrigation reduced control of hemp sesbania and prickly sida and affected efficacy more than soil texture. Single postemergence (POST) applications of glyphosate or fomesafen plus fluazifop-P provided 90% or less control of most weed species. When glyphosate POST or fomesafen plus fluazifop-P POST followed PRE applications of cloransulam or cloransulam plus metribuzin PRE, control of all weeds was generally greater than 85%. The highest soybean yields were recorded from treatments that contained sequential PRE followed by (fb) POST herbicide applications. Composition of weed flora determined the effect of herbicide program on soybean seed yield. No yield benefit was gained from the sequential program when the dominant species was Palmer amaranth, which was controlled by glyphosate. When hemp sesbania was the dominant species, PRE herbicides fb glyphosate POST increased yield compared with total POST glyphosate.

Research was conducted to evaluate corn (Zea mays L.) and soybean (Glycine max L. Merr.) injury and weed control with pyroxasulfone applied preemergence (PRE) and postemergence (POST). In corn, pyroxasulfone applied both PRE at 150 g/ha and POST at 60 g/ha with glyphosate controlled barnyardgrass, Palmer amaranth, sicklepod, prickly sida, browntop millet, ivyleaf morningglory, and entireleaf morningglory 90 to 99% 30 days after the POST application. Weed control was no greater than when pyroxasulfone at 150 g/ha was applied only PRE. Control of barnyardgrass, Palmer amaranth, smooth pigweed, and browntop millet was greater for pyroxasulfone PRE compared with atrazine PRE and lower corn yield was observed for the atrazine treatment. In a second corn study, pyroxasulfone applied alone PRE controlled barnyardgrass, smooth pigweed, Palmer amaranth, hophornbeam copperleaf, sicklepod, ivyleaf morningglory, pitted morningglory, and prickly sida 83 to 100% 66 days after application. Equivalent weed control was obtained for pyroxasulfone plus atrazine and atrazine plus S-metolachlor applied PRE. Corn yield was lower when pyroxasulfone was applied only PRE compared with pyroxasulfone plus atrazine PRE and atrazine plus S-metolachlor PRE. Soybean injury was observed when pyroxasulfone was applied at 60 to 300 g/ha, and at 10 days after application, injury was 2 to 5% when applied PRE and 15 to 21% when applied POST. Injury consisted of crinkling of leaflet surface, irregular leaflet margins, indentation of leaflet tips, and a drooping of leaf petioles (POST application only). Soybean yield was not negatively affected by pyroxasulfone regardless of application timing. In a second soybean study, pyroxasulfone applied alone PRE at 150 g/ha controlled, browntop millet an average of 99%, barnyardgrass 75%, hophornbeam copperleaf 99%, ivyleaf morningglory 86%, hemp sesbania 98%, sicklepod 95% and pitted morningglory 73% around 30 days after treatment. Compared with pyroxasulfone applied alone PRE at 150 g/ha, weed control was not improved when pyroxasulfone was applied PRE with saflufenacil, flumioxazin, fluthicet-methyl, or chlorimuron ethyl plus flumioxazin plus thifensulfuron methyl. Crop safety, consistency in weed control, and flexibility in application timing with pyroxasulfone suggests that it should have a fit in corn and soybean weed management programs in the mid-south.

Palmer amaranth (Amaranthus palmeri S. Wats.) is one of the most difficult weeds to control in soybean (Glycine max (L.) Merr.) in North Carolina. Research was conducted during 2010 and 2011 to determine if Palmer amaranth control and soybean yield were affected by soybean plant population and combinations of preemergence (PRE) herbicides followed by a single application of glufosinate postemergence (POST) versus multiple applications of glufosinate POST. Palmer amaranth was controlled more and soybean yield was greater when soybean was established at 483,000 plants ha−1 in 3 of 4 experiments compared with soybean at 178,000 plants ha−1 irrespective of herbicide treatments. In separate experiments, application of PRE herbicides followed by POST application of glufosinate or multiple POST applications of glufosinate provided variable Palmer amaranth control, although combinations of PRE and POST herbicides controlled Palmer amaranth the most and provided the greatest soybean yield. In 1 of 3 experiments, sequential applications of glufosinate were more effective than a single application. Yield was higher in 2 of 3 experiments when glufosinate was applied irrespective of timing of application when compared with the nontreated control. In the experiment where glufosinate was applied at various POST timings, multiple applications of the herbicide provided the best control and the greatest yield compared with single applications.

Core Ideas Glufosinate + dicamba had similar Palmer amaranth control as glufosinate. Glyphosate + dicamba had similar control as glyphosate. Pre‐emergence followed by post‐emergence and post‐emergence‐only programs had similar control. A Palmer amaranth biotype resistant to photosystem (PS) II‐ and 4‐hydroxyphenylpyruvate dioxygenase (HPPD)‐inhibitor in continuous seed corn production fields in southcentral Nebraska is a management challenge for corn growers. Field studies were conducted on a grower’s field in 2014 through 2016 near Shickley in Fillmore County, Nebraska to determine the efficacy of herbicide programs for control of resistant Palmer amaranth, net economic return, and yield of glyphosate‐ and glufosinate‐resistant corn. Based on contrast analysis, pyroxasulfone + fluthiacet‐ethyl + atrazine applied pre‐emergence (PRE) had the highest (95%) Palmer amaranth control compared with saflufenacil + dimethenamid‐P, mesotrione + S‐metolachlor + atrazine (91 to 92%), and acetochlor + clopyralid + flumetsulam (87%) at 21 d after PRE in 2014 to 2015. Glufosinate or glyphosate alone, or tank‐mixed with dicamba applied post‐emergence (POST)‐only or aforementioned PRE herbicides followed by POST programs had 89 to 99% control at 28 and 72 d after POST in 2014 to 2015. Corn yields and net returns were higher where PRE followed by POST and POST‐only herbicide programs were used compared with PRE‐only programs in glufosinate‐ and glyphosate‐resistant corn in 2014 and 2016. In 2015, corn yields and net returns were similar where PRE‐only, POST‐only, and PRE followed by POST herbicide programs were used in glufosinate‐ and glyphosate‐resistant corn. Results of this study suggest that effective PRE followed by POST herbicide programs are available for controlling PS II‐ and HPPD‐inhibitor‐resistant Palmer amaranth in corn and growers need to adopt an integrated weed management approach to reduce the chances of evolution of herbicide‐resistant weeds.