Corn Injury Research Articles

Discovery of novel arylthioacetic acid derivatives as 4-hydroxyphenylpyruvate dioxygenase inhibitors.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. In a continuing effort to discover novel HPPD inhibitors, we adopted a bioisosterism strategy to design a series of novel arylthioacetic acid scaffold based on the previously discovered aryloxyacetic acid scaffold. This study sheds new light on the discovery of novel HPPD inhibitors. The compounds A1-A30 and B1-B39 were prepared through an efficient synthetic route for in vitro and glasshouse experiments (herbicidal activities, herbicidal activity spectrum, and crop selectivity). Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD inhibitors, compounds A11 (Ki = 0.021 μmol L-1 ) and B20 (Ki = 0.022 μmol L-1 ), which exhibit similar activities to that of mesotrione (Ki = 0.020 μmol L-1 ). The glasshouse experiments data indicated that compounds B34 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. Moreover, molecular simulation results show that the compounds B20, B34, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on herbicidal results, compound B34 was selected for crop selectivity studies (corn injury ≤ 10%), indicating its potential for weed control in corn fields. These bioassay results showed that the compound B34 could be used as a possible lead compound for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Use of the Premix of Atrazine, Bicyclopyrone, S-Metolachlor, and Mesotrione for Weed Control in Corn (Zea mays L.)

Field studies were conducted under conventional tillage from 2014 through the 2018 growing seasons in central, south-central, and the Panhandle regions of Texas to determine corn tolerance and weed efficacy of the four-way premix of atrazine plus bicyclopyrone plus mesotrione plus S-metolachlor (hereafter referred to as ABMS). No corn injury was noted at any location with any ABMS dose or application timing. Preemergence (PRE) applications of ABMS at 2.41 kg ha-1 controlled Palmer amaranth (Amaranthus palmeri S. Wats.) 73 to 100% while smellmelon (Cucumis melo L.) control was 100%. Annual sunflower (Helianthus annuus L.) control with ABMS at 2.41 kg ha-1 was 86% while a split application applied PRE followed by a postemergence (POST) application provided 99% control. Texas millet (Urochloa texana Buckl.) control with ABMS applied PRE ranged from 12 to 35% while broadleaf signalgrass (Brachiaria platyphylla [Griseb.] Nash) control was 100%. Browntop panicum [Urochloa fasciculate (Sw.) R. Webster] control with a PRE application of ABMS at 2.41 kg ai ha-1 was < 82% while jungle rice [Echinochloa colona (L.) Link] control was 98%. Control of a kochia (Kochia scoparia L.) with PRE applications of ABMS at 2.41 kg ha-1 was 95% while the split rate of 1.2 kg ha-1 applied PRE and POST provided 99% control. Corn yields were variable but in most instances all herbicide treatments improved yield over the untreated check. Excellent control of broadleaf weeds was observed with ABMS; however, annual grass control can be variable, especially with large-seeded annual grasses such as Texas millet.

Control of glyphosate/glufosinate-resistant volunteer corn in corn resistant to aryloxyphenoxypropionates

AbstractCorn-on-corn production systems, common in highly productive irrigated fields in South Central Nebraska, can create issues with volunteer corn management in corn fields. EnlistTM corn is a new multiple herbicide–resistance trait providing resistance to 2,4-D, glyphosate, and the aryloxyphenoxypropionate herbicides (FOPs), commonly integrated in glufosinate-resistant germplasm. The objectives of this study were to (1) evaluate ACCase-inhibiting herbicides for glyphosate/glufosinate-resistant volunteer corn control in Enlist corn and (2) evaluate the effect of ACCase-inhibiting herbicide application timing (early POST vs. late POST) on volunteer corn control, Enlist corn injury, and yield. Field experiments were conducted in 2018 and 2019 at South Central Agricultural Laboratory near Clay Center, NE. Glyphosate/glufosinate-resistant corn harvested the year prior was cross-planted at 49,000 seeds ha–1 to mimic volunteer corn in this study. After 7 to 10 d had passed, Enlist corn was planted at 91,000 seeds ha–1. Application timing of FOPs (fluazifop, quizalofop, and fluazifop/fenoxaprop) had no effect on Enlist corn injury or yield, and provided 97% to 99% control of glyphosate/glufosinate-resistant volunteer corn at 28 d after treatment (DAT). Cyclohexanediones (clethodim and sethoxydim; DIMs) and phenylpyrazolin (pinoxaden; DEN) provided 84% to 98% and 65% to 71% control of volunteer corn at 28 DAT, respectively; however, the treatment resulted in 62% to 96% Enlist corn injury and 69% to 98% yield reduction. Orthogonal contrasts comparing early-POST (30-cm-tall volunteer corn) and late-POST (50-cm-tall volunteer corn) applications of FOPs were not significant for volunteer corn control, Enlist corn injury, and yield. Fluazifop, quizalofop, and fluazifop/fenoxaprop resulted in 94% to 99% control of glyphosate/glufosinate-resistant volunteer corn with no associated Enlist corn injury or yield loss; however, quizalofop is the only labeled product as of 2020 for control of volunteer corn in Enlist corn.

Response of soybean and corn to halauxifen-methyl

AbstractPreplant (PP) herbicide applications are an important tool within an integrated weed management system, specifically in no-till production. An understanding of crop tolerance regarding PP applications is important for effectively integrating a new herbicide into no-till cropping systems. Twelve field trials (six in corn and six in soybean) were conducted over a 2-yr period (2018 and 2019) near Exeter and Ridgetown, ON. The purpose of these studies was to evaluate the tolerance of soybean and corn to halauxifen-methyl applied PP, PRE, or POST at the registered rate (5 g a.i. ha−1) and twice the registered rate (10 g a.i. ha−1), hereafter referred to as the 1× and 2× rate, respectively. All trials were kept weed-free throughout the growing season to remove the confounding effect of weed interference. Halauxifen-methyl applied 14 d preplant (DPP), 7 DPP, 1 DPP, and 5 d after seeding (DAS) at the 1× and 2× rates caused ≤10% visible soybean injury. In contrast, halauxifen-methyl applied POST (cotyledon–unifoliate stage, VE-VC) caused 67% to 87% visible soybean injury, a 50% to 53% reduction in height, 65% to 81% decrease in population, 56% to 67% lower biomass, and 53% to 63% decline in yield. Halauxifen-methyl applied 10 DPP, 5 DPP, 1 DPP, 5 DAS, and POST (spike–one leaf stage, VE-V1) at the 1× and 2× rate caused ≤3% visible corn injury and caused no effect on corn height or biomass. Halauxifen-methyl applied at VE-V1 at the 2× rate reduced corn yield 10%. Based on these studies, the current application restriction of 7 DPP in soybean and 5 DPP in corn is conservative and could be expanded. Expanding the application window of halauxifen-methyl would increase the utility of this herbicide for producers.

Tolpyralate + Atrazine Applied Preemergence Provides Residual GR Canada Fleabane [<i>Conyza canadensis</i> (L.) Cronq.] Control Similar to Current Industry Standards

Tolpyralate is a benzoylpyrazole, 4-hydroxyphenyl-pyruvate dioxygenase inhibitor, and a herbicide registered for use in corn. The efficacy of tolpyralate plus atrazine to provide full-season residual control of glyphosate-resistant (GR) Canada fleabane in corn is not known under Ontario environmental conditions. Five field trials were completed over a two-year period (2018-19) in south-western Ontario on farms with confirmed GR Canada fleabane [Conyza canadensis (L.) Cronq.] populations to determine if tolpyralate + atrazine provides full-season residual control of GR Canada fleabane in corn. Corn injury was less than 10% with all treatments. At 4 weeks after application (WAA), tolpyralate (30 g·ai·ha−1), tolpyralate (40 g·ai·ha−1), and atrazine (560 g·ai·ha−1) controlled GR Canada fleabane 64, 78 and 72%, respectively. A tank mix of tolpyralate + atrazine at both rates improved GR Canada fleabane control to 94%. Saflufenacil/dimethenamid-p, mesotrione + atrazine, and dicamba/atrazine controlled GR Canada fleabane 99, 95 and 92%, respectively. At 8 WAA, tolpyralate (30 g·ai·ha−1), tolpyralate (40 g·ai·ha−1) and atrazine (560 g·ai·ha−1) controlled GR Canada fleabane 83, 88, and 83%, respectively (Table 2). The tank mixes of tolpyralate (30 g·ai·ha−1) + atrazine (560 g·ai·ha−1) and tolpyralate (40 g·ai·ha−1) + atrazine (560 g·ai·ha−1) controlled GR Canada fleabane 94, and 97%, respectively, 8 WAA which was similar to saflufenacil/dimethenamid-p, mesotrione + atrazine and dicamba/atrazine. There was no treatment difference for corn yield. Based on these results, tolpyralate (40 g·ha−1), tolpyralate (30 g·ha−1) + atrazine and tolpyralate (40 g·ha−1) + atrazine, applied PRE, provided similar control of GR Canada fleabane as current industry standards at 8 WAA.

Wheat Stem Maggot (Diptera: Chloropidae): An Emerging Pest of Cover Crop to Corn Transition Systems

The wheat stem maggot (Meromyza americana Fitch) (WSM) is a minor pest of wheat, rye, and other grasses. In 2017, growers in Nebraska reported dead center whorls and excessive tillering in early-season cornfields that followed wheat or rye terminated after planting corn. A survey was conducted to evaluate the risk factors for this insect in cover crop to corn transition systems. In each field, management practices and the percentage of injured plants were recorded. Symptomatic corn plants were collected from each field and dissected to determine larval and plant characteristics. In a few cases, small patches of a field were planted to a cover crop to manage soil erosion, and injured plants were only found where the cover crop was present. From these observations, the hypothesis is that terminating a cover crop after planting corn allowed the WSM larva to move from the dying cover crop to corn to complete its development. Cornfields infested with WSM had a frequency of injured corn plants from 0 to 60% with yield losses estimated at 30 bushels/acre. This paper provides the first detailed documentation of WSM injury in corn and addresses important management practices that may have influenced this uncommon situation.

Tank mixture of glyphosate with 2,4-D accentuates 2,4-D injury in glyphosate-resistant corn

Six field trials were conducted at Ridgetown, ON, over a 2-yr period (2015 and 2016) to determine the tolerance of two corn hybrids to 2,4-D (560 and 1120 g a.i. ha−1) and glyphosate (1800 g a.e. ha−1) applied alone or in combination at stage V1, V3, or V5. In DeKalb DKC52-61 corn, 2,4-D caused as much as 24%, 16%, 11%, and 11% visible injury at 1 wk after each postemergence herbicide application (WAT), 2 WAT, 4 wk after the last postemergence herbicide application (WA-C), and 8 WA-C, respectively. Plant stand was not affected, but plant height decreased by 5 cm at 560 g a.i. ha−1 and 7% at 1120 g a.i. ha−1. As the application timing was delayed from stage V1 to V5, there was a trend to increased injury at both 2,4-D rates. Corn yield decreased 8% with 2,4-D applied at 560 g a.i. ha−1 and 12% at 1120 g a.i. ha−1. In Pioneer P0094AM corn, 2,4-D caused as much as 16%, 9%, 7%, and 7% visible injury at 1 WAT, 2 WAT, 4 WA-C, and 8 WA-C, respectively. Plant height was not affected, but goosenecking and brace root malformation were increased as the rate of 2,4-D was increased. There was generally no difference between glyphosate rates (1800 vs 0 g a.e. ha−1) at the V1 corn stage but visible injury, goosenecking, and brace root malformation at other application timings was as much as 15%, 3%, and 19% greater when 2,4-D was applied in a tank mixture with glyphosate, respectively. Yield was reduced by 12% when 2,4-D (1120 g a.i. ha−1) was applied with glyphosate in the tank mixture.

Yellow nutsedge (Cyperus esculentus L.) control in corn with various rates of halosulfuron

There are a limited number of herbicide options that provide commercially acceptable control of yellow nutsedge in corn. A study consisting of nine field experiments was conducted during 2013–2016 in growers’ fields in Ontario to evaluate the efficacy of glyphosate plus various rates of halosulfuron applied after emergence (postemergence, POST) for the control of yellow nutsedge in glyphosate-resistant corn. Glyphosate (900 g a.e. ha−1) plus halosulfuron applied POST at the registered rate of 34–68 g a.i. ha−1 caused minimal injury in glyphosate-resistant corn. The predicted halosulfuron rates needed to control yellow nutsedge 50%, 80%, and 90% were 3, 24, and >140 g a.i. ha−1 at 4 weeks after herbicide application (WAA) and 2, 13, and 73 g a.i. ha−1 at 8 WAA, respectively. The predicted halosulfuron rates required to reduce yellow nutsedge density 50%, 80%, and 90% were 13, 42, and 109 g a.i. ha−1, respectively. In addition, the predicted halosulfuron rates required to reduce yellow nutsedge dry weight 50%, 80%, and 90% were 6, 23, and 54 g a.i. ha−1, respectively. Contrasts comparing halosulfuron (35 g a.i. ha−1) with other herbicides showed that glyphosate plus halosulfuron provided as much as 35% greater control of yellow nutsedge than glyphosate plus bentazon (1080 g a.i. ha−1) and as much as 22% greater control of yellow nutsedge than glyphosate plus tembotrione/thiencarbazone (45 g a.i. ha−1).

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

A premix of atrazine, bicyclopyrone, mesotrione, and S-metolachlor (ABMS) has recently been registered for broad-spectrum weed control in corn (Zea mays L.) in the USA. The objectives of this study were to compare the efficacy of ABMS applied preemergence (PRE) with other commonly used PRE herbicides for weed control, corn injury, and yield in no-tillage (no-till) and reduced-tillage (reduced-till) corn production systems, and to determine the biologically effective doses of ABMS for controlling Palmer amaranth (Amaranthus palmeri S. Wats.) in field conditions. Field experiments were conducted in 2015 and 2016 at South Central Agricultural Laboratory, Clay Center, Nebraska, USA. ABMS applied at the labeled dose (2.89 kg ai ha−1) resulted in 92–99% Palmer amaranth control in both tillage systems. A similar level of Palmer amaranth control (86–99%) was observed with mesotrione plus rimsulfuron in the no-till system; however, the control was higher with ABMS than with other premixes in the reduced-till system at 42 days after treatment (DAT) and at harvest. Applications of ABMS at 2.89 kg ai ha−1 provided 99 and 81% control of velvetleaf (Abutilon theophrasti Medik.) and foxtail (Setaria spp.), respectively, in the no-till system at 28 DAT, whereas control was ≥93% in the reduced-till system. ABMS applied at 2.89 kg ai ha−1 resulted in 3% corn injury at 14 DAT regardless of the tillage system, whereas 15% corn injury was observed with acetochlor plus clopyralid plus flumetsulam, and dimethenamid-P plus saflufenacil in the reduced-till. ABMS or mesotrione plus rimsulfuron at labeled doses resulted in 16.0–16.3 t ha−1 corn yield, comparable to the weed-free control (16.4 t ha−1). The biologically effective doses of ABMS to provide 90% control (ED90) of Palmer amaranth at 42 DAT were 2.44 and 2.81 kg ai ha−1 in no-till and reduced-till systems, respectively. The efficacy of ABMS for broadleaf weed control and early-season grass weed control, and corn yield was the same or sometimes better than most of the PRE herbicides tested in this study; therefore, ABMS can be considered as an additional option for management of problem weeds, including Palmer amaranth in corn in the USA.

Weed Management Programs with Pyroxasulfone in Field Corn (Zea mays)

Field experiments were conducted in Louisiana and Mississippi from 2011 through 2013 to evaluate crop injury, weed control, and yield in field corn following pyroxasulfone applied PRE and POST. Pyroxasulfone PRE or POST did not injure corn at any evaluation. Barnyardgrass control was not improved with the addition of any POST treatment to pyroxasulfone alone or atrazine plus pyroxasulfone PRE; however, all POST treatments increased barnyardgrass control to at least 95% at all evaluations following atrazine PRE. All treatments that contained a PRE followed by POST application controlled browntop millet ≥90% at all evaluations. All POST treatments increased ivyleaf morningglory control to ≥92% following atrazine or pyroxasulfone alone PRE. However, control with atrazine plus pyroxasulfone PRE was similar or greater 28 d after POST than all treatments that received a POST application. In the absence of a POST treatment, pyroxasulfone or atrazine plus pyroxasulfone PRE controlled Palmer amaranth 93 to 96% at all evaluations, but atrazine alone PRE provided 84, 82, and 66% control 7, 14, and 28 d after POST, respectively. All programs that contained a PRE followed by POST herbicide treatment controlled Palmer amaranth >90% at all evaluations. Corn yield following all treatments except atrazine alone PRE and the nontreated were similar and ranged from 10990 to 12330 kg ha−1. This research demonstrated that pyroxasulfone can be a valuable tool for weed management in a corn weed management program.

Comparative Analysis of 2,4-D Uptake, Translocation, and Metabolism in Non–AAD-1 Transformed and 2,4-D–Resistant Corn

The Enlist™ traits provide 2,4-D resistance in several crops. Though corn is naturally tolerant to 2,4-D, the engineered trait conferred by the aryloxyalkanoate dioxygenase-1 (AAD-1) enzyme provides enhanced 2,4-D tolerance and confers resistance to the graminicide herbicide family, the aryloxyphenoxypropionates. The objectives of this research were 2-fold: (1) measure and compare uptake, translocation, and metabolism of 2,4-D in Enlist™ (E, +AAD1) and non–AAD-1 transformed (NT, −AAD1) isogenic corn hybrids; and (2) and investigate the effect of glyphosate and/or the Enlist™ adjuvant system (ADJ) on these factors and corn injury. Uptake of radiolabeled 2,4-D acid applied alone in corn was not altered by the addition of ADJ when tank mixed at 24 h after application (HAA). By contrast, uptake of radiolabeled 2,4-D was significantly lower (69%) compared with 2,4-D plus ADJ (89%) at 24 HAA with a premixed formulation of 2,4-D choline plus glyphosate-dimethylamine (Enlist Duo™ herbicide [EDH]). Translocation of 2,4-D between the two corn hybrids was not different. E corn metabolized more 2,4-D (100% of absorbed) than NT corn (84%), and glyphosate did not alter 2,4-D metabolism. Furthermore, the metabolism of 2,4-D to nonphytotoxic dichlorophenol (DCP) and subsequent DCP-derived metabolites formed in E corn was examined. Injury to E corn is not typically observed in the field; however, injury symptoms were clearly evident in E corn (within 24 HAA) when formulated acetochlor was tank mixed with EDH, which correlated with an increase in 2,4-D uptake during this time period. In summary, the lack of injury in E corn following EDH applied alone may be attributed to a relatively low amount of 2,4-D uptake and the combination of natural and engineered 2,4-D metabolic pathways.

Relative Safety of Preemergence Corn Herbicides Applied to Coarse-Textured Soil

Crop safety is an important consideration in determining PRE herbicide application, especially when multiple herbicide sites-of-action are used. This research examined relative corn injury as the result of PRE applications containing ALS- and/or HPPD-inhibiting herbicides to a sandy loam soil. Herbicide premixes containing clopyralid, flumetsulam, isoxaflutole, mesotrione, rimsulfuron, tembotrione, thifensulfuron, and thiencarbazone were applied at twice the labeled rate. In general, isoxaflutole alone was the safest herbicide evaluated, while PRE applications of rimsulfuron-containing herbicides caused the most corn stunting, had a lower recovery rate, and lower yields. However, POST applications of mesotrione plus rimsulfuron stunted corn less than 2%. Although there was little correlation between corn injury and yield, growers should be aware of the other factors, such as soil texture and environment that may impact crop production.

Biologically effective rate of halosulfuron applied postemergence in corn

There is little information on the biologically effective rate of halosulfuron applied postemergence (POST) for the control of broadleaf weeds in corn under Ontario environmental conditions. Six field trials were conducted over a two-year period (2014, 2015) to determine the biologically effective rate of halosulfuron POST for the control of velvetleaf, pigweed species, common ragweed, common lambsquarters and Eastern black nightshade in corn. Based on regression analysis, the predicted halosulfuron rates required to cause 5, 10 and 20% corn injury were 53, 138 and >560 g ai ha-1 at 1 WAA, 109, 276 and >560 g ai ha-1 at 2 WAA and 493, >560 and >560 g ai ha-1 at 4 WAA, respectively. The predicted halosulfuron rates applied POST for 95% control of velvetleaf, pigweed species, common ragweed, common lambsquarters and Eastern black nightshade were 10-13, 35-143, 25-57, >560 and >560 g ai ha-1, respectively. The predicted halosulfuron rates applied POST to reduce velvetleaf, pigweed species, common ragweed and...

Evaluating Postemergence Herbicides, Safener, and Tolerant Hybrids for Corn Response

Crop safety is one of the many considerations when deciding which POST herbicide to use. This research examined relative corn injury as a result of POST herbicides and the effect of including the safener isoxadifen, the choice of a sensitive or tolerant hybrid, or both. The herbicides included commercial combinations of dicamba, diflufenzopyr, nicosulfuron, rimsulfuron, and thifensulfuron, all at twice the labeled rate. Isoxadifen reduced twisting from dicamba plus diflufenzopyr but not with dicamba plus rimsulfuron. Isoxadifen had negligible effect on chlorosis. In general, rimsulfuron plus thifensulfuron caused the most corn stunting, whereas including isoxadifen or using a tolerant hybrid often reduced corn injury. In two of the four years, treatments with rimsulfuron plus thifensulfuron resulted in yield reductions. Although using products with isoxadifen or selecting tolerant hybrids may influence injury, herbicide selection will have the greatest effect on corn injury.

Corn Injury from Foliar Zinc Application Does Not Affect Grain Yield

Zinc deficiency symptoms have been observed on corn (Zea mays L.) grown on coarse‐textured, high‐pH soils in the Mississippi Delta. To correct deficiencies, many corn producers apply foliar Zn. Corn injury from foliar Zn application has been observed; however, it is not clear whether foliar Zn injury affects grain yield. Also, little information currently exists about the ability of foliar Zn sources to increase corn tissue Zn concentration. Therefore, the purpose of this study was to determine the effect of Zn source and Zn application rate on foliar injury, tissue Zn concentration, and grain yield in corn. Zinc‐citrate, Zn–ethylenediaminetetraacetic acid (EDTA), and ZnSO4 were applied to corn at 0.56, 1.12, and 2.24 kg Zn ha−1 at V4. Corn injury was evaluated 3, 6, and 9 d after application, and tissue Zn concentration was determined 2 wk after Zn application. Grain yield was determined at harvest. Zinc‐citrate imparted the greatest injury at all application rates, followed by ZnSO4 and Zn‐EDTA. Injury generally increased as Zn application rate increased. The 0.56 kg Zn ha−1 rate resulted in similar tissue Zn content across all Zn sources. Zinc‐citrate and ZnSO4 application resulted greater tissue Zn content than Zn‐EDTA at 1.12 and 2.24 kg Zn ha−1 rates. Despite high levels of foliar injury observed for some Zn sources and rates, no differences in grain yield were observed. Citrate‐Zn application to corn caused more foliar injury than EDTA‐Zn and Zinc sulfate. Citrate‐Zn resulted in highest corn tissue Zn concentrations. Corn injury from foliar Zn application did not affect grain yield.

Tratamento de sementes para manejo do percevejo-barriga-verde na cultura de soja e milho em sucessão

Resumo: O objetivo deste trabalho foi avaliar o efeito do tratamento de sementes com inseticidas sobre o manejo de Dichelops melacanthus e a produtividade da soja e do milho, cultivados em sucessão. O estudo foi realizado em campo, nas safras 2012/2013 (I) e 2013/2014 (II). Avaliaram-se os inseticidas imidacloprido, tiametoxam, tiodicarbe, fipronil e abamectina. Determinaram-se: a densidade populacional do percevejo, a produtividade de soja e milho, e a intensidade da injúria em milho. A densidade do percevejo permaneceu abaixo de um inseto por metro quadrado, na maior parte do ciclo da soja. Os picos populacionais foram observados nas primeiras semanas, após a emergência do milho, e atingiram 2,2 (safra I) e 6,7 (safra II) percevejos por metro quadrado. Na cultura da soja, os inseticidas não reduziram a densidade populacional do percevejo. Na cultura do milho, o imidacloprido reduziu a densidade do percevejo em 23,2% (safra I) e 38,8% (safra II), e a injúria em 61,8% (safra I) e 26,4% (safra II). O tiametoxam reduziu a densidade dos insetos em 27,8% (safra II) e a injúria em 42,7% (safra I). O tratamento de sementes com inseticidas não proporciona aumento de produtividade à soja e ao milho, portanto, não se justifica sua utilização nas condições deste estudo.

Examining the plant-back interval for glyphosate/glufosinate-resistant corn after the application of ACCase inhibitors

Field experiments in 2013 and 2014 examined corn (Zea mays L.) tolerance to acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides in a scenario where they would have been used to terminate a failed corn stand prior to replanting. To simulate this, herbicides were applied 1 wk or 1 d preplant (PP) and several parameters were measured. Corn injury 1, 2, 4, or 8 wk after emergence (WAE) was similar to the untreated control, regardless of herbicide, rate, or PP application timing. Across herbicides and rates, PP timing did not affect plant stand and aboveground biomass 2 WAE, plant height 4 WAE, or yield. Across application timings, plant stand and aboveground biomass were similar to the untreated control, regardless of herbicide treatment or rate; however, some herbicides reduced height and (or) yield. For example, compared with the untreated control, fluazifop-p-butyl (75 and 150 g ha−1) and sethoxydim (300 g ha−1) each reduced height by about 3%, while clethodim (30 and 60 g ha−1), fluazifop-p-butyl (150 g ha−1), and quizalofop-p-ethyl (72 g ha−1) each reduced yield by about 2%. Therefore, in situations where a grower may need to terminate a failed corn stand, the selection of ACCase-inhibiting herbicides could be based on efficacy rather than plant-back restrictions.

Weed Control in Corn (Zea maysL.) as Influenced by Preemergence Herbicides

Field studies were conducted in central and south-central Texas from 2013 through 2015 to evaluate crop tolerance and efficacy of various preemergence herbicides alone and in combination for weed control in field corn. Acetochlor and pendimethalin alone,S-metolachlor plus mesotrione, and the three-way combination ofS-metolachlor plus atrazine plus mesotrione provided the most consistent control of annual grasses including browntop panicum (Panicum fasciculatumL.), Texas millet (Urochloa texanaL.), barnyardgrass (Echinochloa crus-galliL.), and sprawling signalgrass (Brachiaria reptansL.). Palmer amaranth [Amaranthus palmeri(S.) Wats.] control was at least 90% with fluthiacet-methyl plus pyroxasulfone, atrazine plus either acetochlor, alachlor, dimethenamid-P,S-metolachlor, orS-metolachlor plus mesotrione, saflufenacil plus dimethenamid-P, andS-metolachlor plus mesotrione. Hophornbeam copperleaf (Acalypha ostryifoliaL.) was difficult to control; however, acetochlor, saflufenacil or pyroxasulfone alone, saflufenacil plus dimethenamid-P, andS-metolachlor plus mesotrione provided at least 90% control. Acetochlor or saflufenacil alone, thiencarbazone-methyl plus isoxaflutole, dimethenamid-P plus atrazine, rimsulfuron plus mesotrione, and saflufenacil plus dimethenamid-P controlled common sunflower (Helianthus annuusL.) at least 90%. Corn injury was minimal (≤3%) with all herbicides. In general, corn grain yield was greatest with herbicide treatments containing more than one active ingredient compared with a single active ingredient.

Field Corn Response to Diclosulam

Crop rotation restrictions often limit the use of diclosulam in peanut (Arachis hypogaea L.). Research was conducted in 2013 and 2014 in Georgia to determine the response of field corn (Zea mays L.) to preemergence (PRE) applications of diclosulam with the intent of simulating carryover from applications made to a previous peanut crop. Diclosulam was applied at 0, 0.0008, 0.0015, 0.003, 0.006, 0.012, 0.024, and 0.047 lb a.i./acre. The normal use rate of diclosulam is 0.024 lb a.i./acre. Corn injury, stand loss, and yield loss increased with diclosulam rate. Diclosulam at 0.0008 lb a.i./acre caused <10% corn injury and <2% plant stand or yield loss. These results suggest that field corn could be safely planted after a field dissipation rate of five half‐lives. The reported half‐life of diclosulam is 13 to 43 days. Thus, it is likely that the field corn rotation restriction could be reduced in the Southeast where corn is grown in warm climates on coarse‐textured soils using supplemental irrigation, which help contribute to optimum microbial degradation of herbicides.

Field horsetail (Equisetum arvense L.) control in corn

Soltani, N., McNaughton, K. and Sikkema, P. H. 2015. Field horsetail (Equisetum arvense L.) control in corn. Can. J. Plant Sci. 95: 983–986. Six field trials were conducted during 2013 and 2014 on various Ontario farms with heavy field horsetail infestations to determine the effectiveness of various postemergence (POST) herbicides for the control of field horsetail in corn. There was minimal and transient corn injury (3% or less) with nicosulfuron/rimsulfuron, flumetsulam or nicosulfuron/rimsulfuron+flumetsulam. In contrast, MCPA amine, nicosulfuron/rimsulfuron+MCPA amine, flumetsulam+MCPA amine, and nicosulfuron/rimsulfuron+flumetsulam+MCPA amine caused as much as 6% injury in corn. Nicosulfuron/rimsulfuron, flumetsulam, MCPA amine, nicosulfuron/rimsulfuron+flumetsulam and nicosulfuron/rimsulfuron+MCPA amine applied POST controlled field horsetail 22–68% and reduced density 27–64% and biomass 38–77%. Flumetsulam+MCPA amine and nicosulfuron/rimsulfuron+flumetsulam+MCPA amine controlled field horsetail 69–83% and reduced density and biomass as much as 87%. Based on these results, flumetsulam+MCPA amine and nicosulfuron/rimsulfuron+flumetsulam+MCPA amine provide the best and most consistent control of field horsetail in corn among POST herbicides evaluated.