Glyphosate Tank Mixtures Research Articles

Long-Term Control of Hedge Bindweed (Calystegia sepium L.) with Single, Tank Mixture, and Sequential Applications of Glyphosate, 2,4-D, and Dicamba

Hedge bindweed (Calystegia sepium L.) is a widespread troublesome perennial weed species that has strong rhizome regenerative capacity. Four pot trials with randomised, complete block designs were conducted in 2015 to evaluate long-term control of hedge bindweed using individual, tank mixture, and sequential applications of selected herbicides. Two different formulations of N-(phosphonomethyl) glycine (glyphosate; isopropylamine, trimesium salts) were applied at 2000 g active ingredient (a.i.) ha−1. Additionally, two synthetic auxins were applied as 3,6-dichloro-2-methoxybenzoic acid (dicamba) at 500 g a.i. ha−1 and the dimethylamine salt of (2,4 dichlorophenoxy)acetic acid (2,4-D) at 1000 g a.i. ha−1. Tank mixtures and sequential applications (12/24 h separation) of these different herbicides were also included. Long-term control of hedge bindweed, Calystegia sepium L., growth was evaluated 8 months after treatments, as comparisons of shoot and rhizome growth (biomass) between untreated and treated plants. There were no differences between the two formulations of glyphosate alone, with shoot and rhizome biomass reductions of 83% and 42%, respectively. Dicamba alone inhibited shoot and rhizome biomass by 86% and 67%, respectively. By itself, 2,4-D provided the greatest reductions in shoot and rhizome biomasses, 93% and 79%, respectively. Antagonism was seen in the tank mixtures of glyphosate and dicamba or 2,4-D. Tank mixtures were generally comparable to treatments of glyphosate alone, and were less effective compared to dicamba or 2,4-D alone. The greatest reduction of bindweed rhizome biomass was for sequential glyphosate trimesium salt followed by 2,4-D 12 h later, thus showing significantly greater efficacy over glyphosate isopropylamine salt (94% vs. 84%; p ≤ 0.05). These data for reductions of the growth of the rhizome biomass show that the sequential application of glyphosate followed by 2,4-D significantly improves long-term control of hedge bindweed.

Herbicide tank mixtures to control co-existing glyphosate-resistant Canada fleabane and giant ragweed in soybean

Populations of glyphosate-resistant (GR) Canada fleabane and GR giant ragweed can be found in several locations in southwestern Ontario. While these species can be managed individually, a scenario has developed where both species are present in GR soybean. Ten separate field experiments (five with Canada fleabane and five with giant ragweed) were conducted over a 2-yr period (2013–2014) in soybean to evaluate preplant (PP) herbicide tank mixtures that could control both weed species if they were present in the same field. Herbicides were rated for soybean injury, weed control, population density, and aboveground biomass. Two- and three-way tank mixtures containing amitrole (i.e., glyphosate + amitrole, glyphosate + amitrole + saflufenacil, and glyphosate + amitrole + 2,4-D) were among the most effective treatments. For example, control of GR Canada fleabane and GR giant ragweed was at least 92% at 4 wk after treatment (WAT) and weed density and biomass were generally similar to the weed-free control. However, without amitrole, the best PP herbicide option was a three-way tank mixture of glyphosate + saflufenacil + 2,4-D which provided improved control and greater reductions in density and biomass compared with the two-way glyphosate tank mixtures containing saflufenacil or 2,4-D.

Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean

Walsh, K. D., Soltani, N., Brown, L. R. and Sikkema, P. H. 2014. Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean. Can. J. Plant Sci. 94: 1239–1244. Six field trials were conducted over a 3-yr period (2011, 2012 and 2013) in Ontario, Canada, to evaluate various postemergence (POST) glyphosate tank mixes for weed management in glyphosate-resistant (GR) soybean. Herbicide treatments included glyphosate applied alone or mixed with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl. Glyphosate tank mixtures with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl caused GR soybean injury of up to 21, 11, 4 and 14% at 7 d after treatment (DAT), which was reduced to 5, 0, 0 and 2% by 28 DAT, respectively. Velvetleaf, green pigweed, common ragweed and common lambsquarters control ranged from 55 to 95, 93 to 100, 70 to 92 and 81 to 98% at 28 DAT respectively. Relative to glyphosate alone, tank mixtures with thifensulfuron-methyl provided equivalent to increased weed control, while acifluorfen, fomesafen and bentazon provided equivalent to reduced weed control. All herbicide tank mixtures resulted in higher yields (3.8–4.0 t ha−1) than the untreated check (2.7 t ha−1), and were generally equivalent to glyphosate alone (4.1 t ha−1). Results from this study indicate that the glyphosate tank mixtures evaluated did not provide a benefit over glyphosate alone.

Summer Annual Weed Control with 2,4-D and Glyphosate

The introduction of 2,4-D-resistant crops stacked with glyphosate resistance will enable the use of 2,4-D and glyphosate for weed control in corn, cotton, and soybean. Because there is little reported on the effectiveness of 2,4-D plus glyphosate on summer annual weed control, the objective was to evaluate 2,4-D and glyphosate tank mixtures on summer annual weed control. Six rates of 2,4-D (0, 280, 420, 560, 840, and 1,120 g ae ha−1) and three rates of glyphosate (0, 840, and 1,120 g ae ha−1) were applied to common lambsquarters, common waterhemp, giant ragweed, giant foxtail, and velvetleaf. Glyphosate at 840 g ha−1controlled all weeds 94 to 100%. Giant ragweed was controlled 99 to 100% by 2,4-D alone when rates were 280 g ha−1or higher. Common lambsquarters, common waterhemp, and velvetleaf control increased as 2,4-D rates increased, with 1,120 g ha−1providing 90 to 94% control.

Selectivity of glyphosate tank mixtures for RR soybean

An active ingredients mixture of different action mechanisms is an essential tool to prevent or manage areas with resistant weeds. However, it is important that such a mixture provides adequate selectivity to the crop. The aim of this work was to evaluate glyphosate selectivity to glyphosate-resistant (RR) soybean, and also verify if there is selectivity in mixtures with other active ingredients applied postemergence aimed at new control strategies, which might be used in RR soybean cultivation. The herbicides and respective rates (g ha-1) evaluated were: glyphosate (720, 960, 1,200, and 1,440), and the mixtures of glyphosate (960) with cloransulam-methyl (30.24), fomesafen (125), lactofen (72), chlorimuron-ethyl (12.5), flumiclorac-pentyl (30), bentazon (480), or imazethapyr (80). All treatments were applied in postemergence when the soybean crop was at V2 to V3 stage. Treatments with glyphosate or in mixtures with postemergent herbicides showed visual effects of phytotoxicity when applied to the glyphosate-resistant soybean. Effects such as reduction in plant height, crop closure, number of pods per plant, and hundred grain weight could be observed. However, the effects related to plant development were mostly transient and did not persist during the crop cycle. Among the studied treatments, only the mixture of glyphosate and lactofen was not selective to the crop, promoting negative effects on most characteristics analyzed and consequently reducing grain yield.

Misturas em tanque com glyphosate para o controle de trapoeraba, erva-de-touro e capim-carrapicho em soja RR®

O uso de misturas de glyphosate, em tanque, para manejo de espécies de plantas daninhas de difícil controle tem sido prática comum entre os agricultores brasileiros. Desta forma, este trabalho teve como objetivo avaliar a eficácia e seletividade de misturas, em tanque, de herbicidas com glyphosate para o controle de trapoeraba (Commelina benghalensis L.), erva-de-touro (Tridax procumbens L.) e capim-carrapicho (Cenchrus echinatus L.) na cultura da soja RR®. O experimento foi conduzido em Maracaí, São Paulo, no período de novembro de 2006 a março de 2007, utilizando-se o cultivar CD-214RR® e delineamento experimental de blocos ao acaso, com 21 tratamentos e quatro repetições. Os tratamentos foram constituídos da aplicação de: glyphosate (180; 360; 540 e 720 g ha-1); glyphosate em sequencial (180/360; 360/360 e 540/360 g ha-1); glyphosate + chlorimuron-ethyl 360+10; 540+10; 360+5/ 360+5 g ha-1); glyphosate + lactofen (360+120; 540+120; 360+60/ 360+60 g ha-1); glyphosate + cloransulam-methyl (360+30; 540+30; 360+16,9/ 360+12,9 g ha-1); glyphosate + carfentrazone (360+4 g ha-1); glyphosate + imazethapyr (360+50 g ha-1); glyphosate + imazethapyr (177,8+30 g ha-1) e testemunhas capinada e sem capina. Apesar da similaridade de produtividade de grãos entre os tratamentos com glyphosate isolado e sequencial, nas doses 540, 720 e 540/ 360 g ha-1, as misturas em tanque com chlorimuron-ethyl, cloransulam-methyl, lactofen e imazethapyr favoreceram o controle de espécies de plantas daninhas tolerantes ao glyphosate como C. benghalensis e T. procumbens.

Eficiência e qualidade da aplicação de misturas em tanque com adjuvantes na dessecação de corda-de-viola

O objetivo do trabalho foi avaliar se a utilização de adjuvantes nas misturas em tanque de glyphosate + chlorimuron-ethyl e glyphosate + carfentrazone-ethyl influenciam na qualidade da aplicação e eficiência de controle de Ipomoea grandifolia. Treze tratamentos, dispostos em delineamento inteiramente casualizado, foram constituídos pelas misturas em tanque de glyphosate + chlorimuron-ethyl (1.440 + 12,5 g ha-1) e glyphosate + carfentrazone-ethyl (1.440 + 10 g ha-1) isoladas e associados aos adjuvantes Nimbus®, Joint Oil®, Naturl'Oil®, Triunfo 515® e All Fix ®, e uma testemunha sem aplicação. Os adjuvantes utilizados foram eficientes na redução da tensão superficial das caldas; no entanto, não influenciaram nos valores de deposição e na eficiência do controle. Os adjuvantes proporcionaram efeitos distintos na redução da tensão superficial, no pH e na qualidade da aplicação (diâmetro mediano volumétrico, densidade de gotas, potencial de perdas por deriva, área coberta e diâmetro médio das gotas) das misturas em tanque de glyphosate + chlorimuron-ethyl e glyphosate + carfentrazone-ethyl, mas não interferiram na deposição da calda de pulverização sobre os alvos I. grandifolia e lâminas de vidro. Glyphosate + carfentrazone-ethyl apresentou maior velocidade de controle de I. grandifolia em relação ao glyphosate + chlorimuron-ethyl, na ausência ou na presença dos adjuvantes, apesar de o glyphosate + carfentrazone-ethyl associado com Nimbus® e Joint Oil® terem proporcionado às plantas-alvo início de desenvolvimento de novas folhas.

Control of Glyphosate-Resistant and Glyphosate-Sensitive Giant Ragweed in Soybean with Adjuvant, Fomesafen, and Glyphosate Tank Mixtures

Field research was conducted to determine the effectiveness of glyphosate, fomesafen, and adjuvant combinations on 6-inch glyphosate-resistant (GR) and 12-inch glyphosate-sensitive (GS) giant ragweed. Glyphosate alone controlled GS giant ragweed greater than 93%, but control of GR giant ragweed was less than 47%. GS and GR giant ragweed responded similarly to fomesafen as control ranged from 42 to 86%. Control with reduced rates of fomesafen was enhanced with additional adjuvants. Regardless of adjuvant, the labeled use rate of fomesafen alone at 0.352 lb/acre provided 75 to 86% control of both GR and GS giant ragweed. The addition of glyphosate to fomesafen resulted in over 90% control of GS giant ragweed. The addition of glyphosate to fomesafen did not improve control of GR giant ragweed and when additional adjuvants were not used, control was reduced when glyphosate was added to 0.352 lb/acre of fomesafen.

Selectivity of glyphosate in tank mixtures for RR soybean in sequential applications with mixtures only in the first or second application

Tank mixtures among herbicides of different action mechanisms might increase weed control spectrum and may be an important strategy for preventing the development of resistance in RR soybean. However, little is known about the effects of these herbicide combinations on soybean plants. Hence, two experiments were carried out aiming at evaluating the selectivity of glyphosate mixtures with other active ingredients applied in postemergence to RR soybean. The first application was carried out at V1 to V2 soybean stage and the second at V3 to V4 (15 days after the first one). For experiment I, treatments (rates in g ha-1) evaluated were composed by two sequential applications: the first one with glyphosate (720) in tank mixtures with cloransulam (30.24), fomesafen (125), lactofen (72), chlorimuron (12.5), flumiclorac (30), bentazon (480) and imazethapyr (80); the second application consisted of isolated glyphosate (480). In experiment II, treatments also consisted of two sequential applications, but tank mixtures as described above were applied as the second application. The first one in this experiment consisted of isolated glyphosate (720). For both experiments, sequential applications of glyphosate alone at 720/480, 960/480, 1200/480 and 960/720 (Expt. I) or 720/480, 720/720, 720/960 and 720/1200 (Expt. II) were used as control treatments. Applications of glyphosate tank mixtures with other herbicides are more selective to RR soybean when applied at younger stages whereas applications at later stages might cause yield losses, especially when glyphosate is mixed with lactofen and bentazon.

Seletividade de cultivares de soja RR® submetidos a misturas em tanque de glyphosate + chlorimuron-ethyl associadas a óleo mineral e inseticidas

O uso de glyphosate para o controle de plantas daninhas em soja RR® apresenta características essenciais no conceito de praticabilidade. Entretanto, apesar de não permitido na legislação brasileira, tem-se aumentado a associação com outros herbicidas para manejo de espécies de difícil controle, assim como a sua mistura em tanque em combinação com inseticidas e adjuvantes. Com o objetivo de avaliar a seletividade de cultivares de soja RR® submetidos a misturas em tanque de formulações de glyphosate (Polaris®, Roundup Ready® e Roundup WG®) com chlorimuron-ethyl (Classic®), e suas associações com óleo mineral (Joint Oil®) e inseticidas novaluron (Gallaxy 100 EC®), permethrin (Piredan®) e methomyl (Lannate BR®), um experimento foi conduzido a campo na cidade de Maracaí-SP, na safra 2006/2007. O delineamento experimental utilizado foi o de blocos ao acaso, com quatro repetições, em esquema fatorial 16 x 4, sendo 16 as associações das misturas em tanque entre as formulações de glyphosate, óleo mineral e inseticidas e quatro cultivares: Monsoy 7210RR®, Monsoy 7979RR®, BRS 245RR® e CD 214RR®. Sintomas visuais de intoxicação inicial dos cultivares estudados foram caracterizados por clorose e encarquilhamento nas folhas para todas as misturas em tanque das formulações de glyphosate + chlorimuron-ethyl, associadas ou não ao óleo mineral e inseticidas novaluron, permethrin e methomyl. Todas as misturas em tanque não promoveram reduções significativas de produtividade para os cultivares Monsoy 7210RR®, Monsoy 7979RR® e BRS 245RR® e controlaram Ipomoea spp. com eficácia apenas satisfatória a partir dos 21 DAA (dias após aplicação).

Evaluation of Glyphosate-Resistant Hard Red Spring Wheat (Triticum aestivum)

The potential for future commercialization of glyphosate-resistant wheat necessitates evaluation of agronomic merits of this technology. Experiments were established to evaluate glyphosate-resistant wheat and weed responses to glyphosate rate, application timing, and tank mixtures. Glyphosate at 1,680 g/ha did not injure wheat. Wheat response to glyphosate applied to one- to three- or three- to five-leaf wheat was not different from that of untreated wheat. Wheat was injured more from glyphosate plus thifensulfuron or glyphosate plus dicamba than from individual herbicides at one of six locations, but grain yield was not affected by glyphosate tank mixtures. Glyphosate application timing did not affect control of wild oat or common lambsquarters 56 d after treatment. Glyphosate when applied to one- to three-leaf wheat provided better control of wild buckwheat than later glyphosate application, whereas glyphosate applied to three- to five-leaf wheat provided the best control of green and yellow foxtail, redroot pigweed, and Canada thistle. Weed control with glyphosate tended to be better than with conventional herbicides, and wheat treated with glyphosate produced approximately 10% more grain than wheat treated with conventional herbicide tank mixes.

Efficacy and Economics of Weed Control Programs in Glyphosate-Resistant Potato (Solanum tuberosum)1

Field studies were conducted to evaluate weed control, tuber yield, gross return, economic return on investment (EROI), and net return in glyphosate-resistant ‘Ranger Russet’ potato in 2000 and 2001 at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. Three types of weed control programs were evaluated: a total glyphosate program of single or sequential applications (TGLY), tank mixtures of glyphosate and residual herbicides applied early postemergence (GLY + RES EPOST), and residual preemergence herbicides followed by (fb) a late postemergence glyphosate application (RES PRE fb LPOST GLY). A standard rimsulfuron + metribuzin + nonionic surfactant EPOST treatment was included for comparison. The standard EPOST treatment and all glyphosate-containing treatments controlled hairy nightshade 88 to 99%. RES PRE fb LPOST GLY treatments improved hairy nightshade control compared with the RES PRE components applied alone. All herbicide treatments controlled kochia 87 to 99% and gre...

Residual Herbicides used in Combination with Glyphosate and Glufosinate in Corn (Zea mays)1

Weed management strategies are needed to control weeds in corn that emerge after postemergence (POST) application of glyphosate or glufosinate. Field trials were conducted from 1996 to 1999 to determine if residual herbicides could be used with glyphosate or glufosinate to provide season-long weed control in glyphosate-resistant or glufosinate-resistant corn. Preemergence (PRE) applications of several residual herbicides followed by POST applications of glyphosate or glufosinate were compared with POST tank mixtures of glyphosate or glufosinate with residual herbicides. All residual herbicides used in combination with glyphosate, when compared with glyphosate alone, increased control of redroot pigweed and common lambsquarters by an average of 20% and resulted in a 4 to 19% increase in control of giant foxtail. Each residual herbicide tank mixture with glufosinate, when compared with glufosinate alone, increased control of common ragweed and giant foxtail. In most instances, weed control was similar for t...

Glyphosate em mistura com herbicidas alternativos para o manejo de plantas daninhas

O uso intensivo de glyphosate como herbicida não-seletivo tem selecionado espécies de plantas daninhas tolerantes. Dessa forma, é importante que sejam estudadas misturas de tanque com herbicidas de mecanismos de ação alternativos e que apresentem efeitos sinergísticos ou aditivos. Por essa razão, foi instalado um experimento inteiramente casualizado, composto por 13 tratamentos e 4 repetições, em casa de vegetação da Universidade de São Paulo - ESALQ/USP, Piracicaba-SP, com as plantas daninhas Richardia brasiliensis, Commelina benghalensis, Amaranthus hybridus, Galinsoga parviflora e Ipomoea grandifolia em misturas de tanque dos herbicidas chlorimuron-ethyl, sulfentrazone, carfentrazone, bentazon ou flumioxazin com glyphosate. As interações foram aditivas para as plantas daninhas I. grandifolia e C. benghalensis, e os herbicidas flumioxazin, sulfentrazone e carfentrazone aplicados isoladamente e em mistura com glyphosate foram os que proporcionaram os melhores níveis de controle. A interação de glyphosate com sulfentrazone foi antagônica em R. brasiliensis; a mistura de glyphosate com os demais herbicidas estudados foi aditiva, sendo os tratamentos com mistura de glyphosate e chlorimuron-ethyl ou flumioxazin os mais eficazes. Em A. hybridus, os tratamentos que apresentaram melhores níveis de controle foram o glyphosate e carfentrazone, aplicados isoladamente, e a mistura de glyphosate com flumioxazin, sulfentrazone, chlorimuron-ethyl e bentazon, sendo estes interações aditivas. No caso de G. parviflora, os tratamentos com flumioxazin e sulfentrazone apresentaram controle total, o mesmo acontecendo com as misturas de glyphosate com carfentrazone, flumioxazin, sulfentrazone, chlorimuron-ethyl ou bentazon.

Incorporating CGA-248757 and Flumiclorac into Annual Weed Control Programs for Corn (Zea mays) and Soybean (Glycine max)1

Field trials evaluated weed control in corn and soybean with CGA-248757 and flumiclorac. CGA-248757 and flumiclorac were applied to 5-, 45-, and 60-cm-tall velvetleaf. Visual control ratings 7 d after treatment (DAT) indicated the greatest control of velvetleaf in corn with CGA-248757 applied to velvetleaf when 5 or 45 cm tall, whereas the greatest control with flumiclorac occurred when applied to 5-cm-tall velvetleaf. However, ratings 21 DAT to 60-cm-tall velvetleaf indicated velvetleaf control with both herbicides was greatest when applied to plants 45 or 60 cm tall. CGA-248757 or flumiclorac applied postemergence (POST) following metolachlor or metolachlor plus atrazine preemergence (PRE) improved velvetleaf control compared with metolachlor plus atrazine alone. Similarly, tank mixtures of CGA-248757 or flumiclorac with 2,4-D following metolachlor PRE provided greater velvetleaf control compared with metolachlor PRE followed by 2,4-D POST. Velvetleaf control in corn was greater when CGA-248757 or flumiclorac were tank mixed with nicosulfuron plus atrazine or nicosulfuron plus dicamba. In soybean, metolachlor plus metribuzin plus clomazone PRE, metolachlor PRE followed by flumiclorac POST, and metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST provided greater than 85% control of giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf 56 d after POST treatments (DAPO) in 1997. Additionally, glyphosate applied late postemergence (LPOST) and tank mixtures of glyphosate with CGA-248757 or flumiclorac LPOST provided greater than 90% control of these same weed species in 1997. However, only metolachlor plus metribuzin PRE followed by CGA-248757 or flumiclorac POST and imazethapyr plus CGA-248757 or flumiclorac POST provided greater than 80% giant foxtail, common lambsquarters, redroot pigweed, and velvetleaf control 56 DAPO in 1998.Nomenclature: Atrazine; 2,4-D; CGA-248757 (proposed common name, fluthiacet), methyl[[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H,3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; clomazone; dicamba; flumiclorac; glyphosate; imazethapyr; metolachlor; metribuzin; nicosulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L. # ZEAMA; giant foxtail, Setaria faberi Herrm. # SETFA; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr. # GLYMA; velvetleaf, Abutilon theophrasti Medik. # ABUTH.Additional index words: Antagonism, herbicide interaction, Protox, bromoxynil, clethodim, oxasulfuron, quizalofop, sethoxydim, ABUTH, AMARE, CHEAL, DIGSA, GLYMA, SETFA, XANST, ZEAMA.Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAPO, days after postemergence treatment; DAT, days after treatment; LPOST, late postemergence; NIS, nonionic surfactant; POST, postemergence; Protox, protoporphyrinogen oxidase; PRE, preemergence; UAN, 28% urea ammonium nitrate.

Interaction of glyphosate with postemergence soybean (Glycine max) herbicides

Greenhouse and field experiments were conducted to evaluate the potential for antagonistic or synergistic interactions from tank mixtures of glyphosate plus a selective herbicide applied postemergence. In the greenhouse, glyphosate at 420 g ae ha−1plus 28% liquid urea-ammonium nitrate (28% UAN) provided at least 89% control of common lambsquarters and common ragweed. Glyphosate at 1,680 g ha−1plus 28% UAN provided less than 81% control of velvetleaf and less than 75% control of ivyleaf morningglory. Tank mixing bentazon at 1,120 g ai ha−1with glyphosate at 420 g ha−1synergistically increased control of velvetleaf. Tank mixtures of glyphosate plus a selective herbicide were predominately additive in control of common lambsquarters, common ragweed, and velvetleaf. Several tank mix combinations of chlorimuron or imazethapyr plus glyphosate plus 28% UAN were antagonistic in control of ivyleaf morningglory. In the field, glyphosate at 840 g ha−1plus 28% UAN provided at least 88% control of common lambsquarters and velvetleaf in 1994. However, glyphosate at 840 g ha−1plus 28% UAN provided only 60% control of velvetleaf in 1995. Tank-mixing bentazon or CGA-248757 with glyphosate at 420 g ha−1increased velvetleaf and common lambsquarters control in 1995. In general, adding chlorimuron, imazethapyr, or thifensulfuron to glyphosate plus 28% UAN did not increase control of common lambsquarters or velvetleaf. Tank mixing imazethapyr with glyphosate plus 28% UAN antagonized velvetleaf control in 1994 and in 1995. The tank mixture of thifensulfuron at 2 g ha−1plus glyphosate at 420 g ha−1plus 28% UAN increased soybean injury in the field in 1994. However, tank mixing chlorimuron, imazethapyr, or thifensulfuron with glyphosate plus 28% UAN did not increase soybean injury in the greenhouse or in the field in 1995.

Influence of Residual Herbicides on Rate of Paraquat and Glyphosate in Stale Seedbed Soybean (Glycine max)

Field studies were conducted to evaluate weed control with paraquat and glyphosate applied at various rates alone and in combination with residual herbicides. Morningglory, prickly sida, and hemp sesbania control 28 d after treatment was similar regardless of herbicide treatment. In contrast, barnyardgrass control when paraquat was tank mixed with pendimethalin plus imazaquin was equal to that of paraquat alone but less than that for tank mixtures with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin. Barnyardgrass control and soybean yield when paraquat was applied at 1050 g ai/ha in combination with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin was greater than when the same residual herbicide treatments were applied with paraquat at 350 g/ha. Yield following glyphosate at 840 and 1120 g ai/ha in combination with residual herbicides was no greater than when glyphosate was applied alone, which was reflective of barnyardgrass control. Tank mixtures of glyphosate at 1680 g/ha with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin resulted in soybean yield higher than for glyphosate alone. Regardless of the glyphosate and residual herbicide combination, soybean yield was no greater than when paraquat was applied at 350 g/ha in combination with metolachlor plus metribuzin plus chlorimuron.