Applications Of Glufosinate Research Articles

Evaluation of Postemergence Weed Control Programs in Cotton Without the Addition of Glyphosate

Glyphosate has played an important role in agricultural production systems, especially after the release of glyphosate resistant crops. With increased usage and an overall reliance on chemical control, weed resistance to glyphosate has occurred and is now a major issue. The objective of this research was to investigate weed control levels provided by glufosinate, 2,4-D, and clethodim as an alternative to glyphosate. Multiple POST applications generally provided superior weed control in comparison to a single early-POST application. No programs provided greater than 80% warm-season grass control beginning 21 d after mid-POST application. Applications of glufosinate or glufosinate + 2,4-D fb clethodim + glufosinate, glufosinate + 2,4-D, or clethodim + glufosinate + 2,4-D provided adequate broadleaf weed control throughout the rating period. Although POST-only programs are an option, they are not a sustainable weed control practice. It remains important to incorporate residual herbicides into a weed control program as well as alternative weed control methods.

Confirmation of a four-way herbicide-resistant Palmer amaranth (Amaranthus palmeri) population in Iowa

Abstract Palmer amaranth (Amaranthus palmeri S. Watson) was first reported in Iowa in 2013 and has continued to spread across the state over the last decade. Importantly, A. palmeri is widely recognized as one of the more economically important weeds in production agriculture. The presence of A. palmeri in Iowa is concerning as the species has evolved resistance to nine herbicide sites of action, however, no formal characterization has been conducted on Iowa populations. Therefore, herbicide assays were conducted on an A. palmeri population collected in Harrison County, Iowa in 2023 (Southwest Palmer Amaranth, SWPA) and a known herbicide-susceptible population collected from Nebraska in 2001 (Palmer Amaranth Susceptible, PAS). The two populations were treated with preemergence and postemergence herbicides commonly used in Iowa. The treatments included preemergence applications of atrazine, metribuzin, and mesotrione and postemergence applications of atrazine, imazethapyr, glyphosate, lactofen, mesotrione, glufosinate, 2,4-D and dicamba at 1x and 4x the labeled rates. Survival frequency of SWPA was >90% when treated postemergence with 1x rates of imazethapyr, atrazine, glyphosate, and mesotrione compared to ≤6% for PAS. Both SWPA and PAS had 0% survival when treated with lactofen, glufosinate, 2,4-D, and dicamba at the 1x or 4x rates. Plant population density reduction for SWPA was 53% and 40% in response to 1x rates of preemergence-applied mesotrione and atrazine, respectively. Metribuzin applied preemergence reduced SWPA plant population density by >90% at both rates. Dose-response experiments revealed the 50% effective doses (ED50) of mesotrione, glyphosate, imazethapyr, and atrazine for SWPA were 9.5-,8.5-, 71- and 40-fold greater than for PAS, respectively. The results confirm that SWPA is four-way multiple herbicide-resistant. Amaranthus palmeri infestations are likely to continue to spread within Iowa, therefore diversified weed management programs that include early detection, rapid response, and effective multi-tactic management strategies will be required for control.

Control of giant ragweed (Ambrosia trifida) in mesotrione-resistant soybean

Abstract Preemergence applications of mesotrione, an herbicide that inhibits 4-hydroxyphenolpyruvate dioxygenase (HPPD), have recently gained regulatory approval in soybean varieties with appropriate traits. Giant ragweed is an extremely competitive broadleaf weed, and biotypes resistant to acetolactate synthase inhibitors (ALS-R) can be particularly difficult to manage with soil-residual herbicides in soybean production. This study investigated control of giant ragweed from preemergence applications of cloransulam (32 g ai ha–1), metribuzin (315 g ai ha–1), and S-metolachlor (1,600 g ai ha–1) in a factorial design with and without mesotrione (177 g ai ha–1) at two different sites over 2 yr. Treatments with mesotrione were also compared with two commercial premix products: sulfentrazone (283 g ai ha–1) and cloransulam (37 g ai ha–1), and chlorimuron (19 g ai ha–1), flumioxazin (69 g ai ha–1), and pyroxasulfone (87 g ai ha–1). At 42 d after planting, control and biomass reduction of giant ragweed were greater in treatments with mesotrione than any treatment without mesotrione. Giant ragweed biomass was reduced by 84% in treatments with mesotrione, whereas treatments without mesotrione did not reduce biomass relative to the nontreated. Following these preemergence applications, sequential herbicide treatments utilizing postemergence applications of glufosinate (655 g ai ha–1) plus fomesafen (266 g ai ha–1) and S-metolachlor (1,217 g ai ha–1) resulted in at least 97% control of giant ragweed at 42 d after planting, which was greater than sequential applications of glufosinate alone in 3 of 4 site-years. Preemergence applications of mesotrione can be an impactful addition to soybean herbicide programs designed to manage giant ragweed, with the potential to improve weed control and delay the onset of herbicide resistance by providing an additional effective herbicide site of action.

Growth and fecundity of Palmer amaranth escaping glufosinate in soybean with and without grass competition

Abstract Field experiments were conducted at Clayton and Rocky Mount, North Carolina, during the summer of 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in soybean crops. Glufosinate (590 g ai ha−1) was applied at early postemergence (when Palmer amaranth plants were 5 cm tall), mid-postemergence (7–10 cm), and late postemergence (>10 cm) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy (i.e., intraspecific and grass competition), weed-free in-crop (WFIC), and weed-free fallow (WFNC) conditions for comparisons. No Palmer amaranth plants survived the sequential glufosinate applications and control decreased as the plants were treated at a larger size in both experiments. The apical and circumferential growth rate of Palmer amaranth surviving glufosinate was reduced by more than 44% compared with the WFNC Palmer amaranth. The biomass of Palmer amaranth plants that survived glufosinate was reduced by more than 87% compared with the WFNC Palmer amaranth. The fecundity of Palmer amaranth that survived glufosinate was reduced by more than 70% compared with WFNC Palmer amaranth. Palmer amaranth plants that survived glufosinate were as fecund as the WFIC Palmer amaranth in both experiments in soybean fields. The results prove that despite the significant vegetative growth rate decrease of Palmer amaranth that survived glufosinate, plants can be as fecund as nontreated plants. The trends in growth and fecundity of Palmer amaranth that survives glufosinate with and without grass competition were similar. These results suggest that glufosinate-treated grass weeds may not reduce the growth or fecundity of Palmer amaranth that survives glufosinate.

Direct and indirect effects of Basta®, a glufosinate-based herbicide, on banana plantation soil microbial diversity and function

Herbicide applications have doubled over the past 30 years to control weeds, but their use may influence soil microbial communities, which mediate important ecosystem services. Here, we characterised the direct effects of a single application of Basta® (glufosinate), at 1× and 2× the recommended rate (5 and 10 kg product ha−1), as well as the indirect effects of vegetation loss on the diversity and function of soil microbial communities within a banana plantation. A 10-month pre-experimental period using Basta® to remove additional vegetation from half of the experimental area created conditions for assessing the indirect herbicide effects. Direct assessments on soil microbial communities began when the Basta® herbicide treatments were applied to the areas with and without vegetation and continued over multiple time-points, for 56 days. Herbicide treatment had no significant direct impacts on basal, and substrate induced respiration rates, or the potential activities of microbial enzymes as inferred from fluorescein diacetate hydrolysis (FDA) and β-glucosidase assays. Similarly, phylogenetic marker gene sequencing indicated that Basta® application did not significantly influence the diversity of soil bacterial or fungal communities. Indirectly, Basta® had a greater influence on the soil microbial activity and functions by removing understory vegetation cover around banana plants. This suggested that continual use of herbicides to reduce soil vegetation cover under bananas had a greater impact on soil microbial communities than a single application of the herbicide. Furthermore, the presence or absence of vegetation cover, significantly altered the abundance of Fusarium oxysporum, plus an additional eight bacterial and ten fungal taxa. Our results indicated that a single application of glufosinate as Basta® at the recommended or double the recommended rate, did not adversely affect soil microbial communities or their activities in banana plantations directly. However, application of herbicides, such as Basta® in crops like banana, indirectly alters soil microbial communities and their activities through loss of vegetation cover and should only be used as a component of an integrated weed management system.

Early detection of the herbicidal effect of glyphosate and glufosinate by using hyperspectral imaging

AbstractEarly detection of non‐optimal weed control is now a priority to ensure herbicide efficacy. This study aimed to evaluate the potential of hyperspectral imaging (HSI) for early detection of the effects of glyphosate and glufosinate on weeds. Specific features (bands and vegetation indices [VIs]) were extracted as indicators for glyphosate and glufosinate efficacy. Black nightshade (Solanum nigrum L.) was used as the model weed and treated with glyphosate or glufosinate at the fourth‐leaf stage. Plants were imaged in the laboratory at 6, 24, 48, 72, and 96 hours after treatment (HAT) with a 204‐wavelength (400–1000 nm) hyperspectral camera. The impact of the herbicide treatments on the spectral reflectance values was analyzed using the two‐sided Mann–Whitney U test, followed by classification with a machine learning (ML) model applied on the full spectrum and on 12 VIs. In addition, the contribution of the different wavelengths (features) to classification accuracy was assessed using a feature selection process. For glufosinate, 95% classification accuracy was observed as early as 6 HAT, with four features from the green region required. For glyphosate, four features from the red, red‐edge, and green regions were used to achieve 88% classification accuracy at 24 HAT. The accuracy of VIs‐based classification was generally lower than that of the full spectrum classification accuracy. Above 85% classification accuracy was achieved only at later imaging campaigns, starting at 48 HAT. This study thus demonstrates that non‐optimal application of glyphosate and glufosinate can indeed be detected using spectral imaging.

Effect of herbicides on the emergence of Sitophilus zeamais (Coleoptera: Curculionidae) in transgenic Bt maize

etically modified organisms (GMOs) are widespread in Brazil, especially those related to resistance to herbicides and insects. This work aimed to evaluate herbicides' effect on the emergence of maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) in different maize genotypes. The experimental design was a 3 × 5 factorial experiment in a randomized complete block design with four replications. Genotypes of transgenic maize, Herculex® (TC1507) and PowerCore® (MON89034 × TC1507 × NK603) and an Isohybrid (non-transgenic) were used. The herbicides were Atrazine, Atrazine + Nicosulfuron, Ammonium Glufosinate, Nicosulfuron and a control treatment without herbicide application. The emergence of S. zeamais was observed in grains from each plot for 100 days, with 300 grams of maize grains. The Isohybrid was the most attractive to S. zeamais when no herbicide was applied. The application of Ammonium Glufosinate increased S. zeamais preference for Herculex® and Nicosulfuron for PowerCore®. The insertion of an exogenous gene and the application of herbicides in maize plants can alter components of the insect-plant interaction, changing the attractiveness to S. zeamais.

Late postemergence glufosinate‐based programs for glyphosate‐resistant Palmer amaranth control in dicamba/glufosinate/glyphosate‐resistant soybean

AbstractGlyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) is widespread in the Central Great Plains. Introduction of newly developed dicamba/glufosinate/glyphosate (DGG)‐resistant soybean varieties allows postemergence (POST) applications of dicamba and glufosinate for in‐season control of GR Palmer amaranth. Limited information exists on the effectiveness of glufosinate applied late‐POST for tall (70–90 cm) GR Palmer amaranth control in DGG‐resistant soybean. The objectives of this study were to (1) determine the effectiveness of late‐POST glufosinate‐based programs for GR Palmer amaranth control, and (2) determine the impact of those programs on soybeans grain yields. Ten glufosinate‐based programs were tested in a field study at Kansas State University Agricultural Research Center near Hays, Kansas. Results indicated that single (655 or 737 g ha−1) and all sequential (594 followed by [fb] 594, 655 fb 594, and 737 fb 594 g ha−1) applications (7‐days apart) of glufosinate provided 87%–93% control of GR Palmer amaranth 28 days after last POST (DALPOST). Palmer amaranth control with single late‐POST application of glufosinate (594 g ha−1) or glufosinate plus S‐metolachlor did not exceed 84% at 28 DALPOST. Majority of the evaluated programs reduced shoot dry weights of GR Palmer amaranth by 83%–91%. The least control (11%) and shoot dry weight reduction (33%) of GR Palmer amaranth were observed with glyphosate fb glyphosate. Glufosinate‐based programs resulted in soybean grain yield of 626–701 kg ha−1. These results conclude that glufosinate applied late‐POST may provide effective control of tall GR Palmer amaranth in DGG‐resistant soybeans.

CHEMICAL CONTROL OF GARDEN SPURGE MATURE PLANTS (Chamaesyce hirta) IN THE FIELD

Chamaesyce hirta is a troublesome weed in producing regions of Brazil; however, little is knownabout the control of adult plants. We evaluated the control of adult Chamaesyce hirta plants in the field. Theexperiment was installed at COACEN, municipality of Sorriso - MT, in a randomized complete block design, withfour replicates. Treatments were arranged in a split plot factor, where plots received the application of 19 herbicidesin burndown and subplots received the sequential application of paraquat, glufosinate ammonium, or no herbicide,nine days after the first application. Visual control evaluations were performed at 7, 14, 21 and 28 days after thefirst application and at 5, 12 and 19 days after the second application. Sequential applications increased the levelof control of most treatments. Isolated glyphosate applications, without sequential application did not control C.hirta. The addition of saflufenacil to glyphosate + 2,4-D mixture provides effective control with a single application.The mixture of glyphosate + 2,4-D provided better control than glyphosate + chlorimuron-ethyl and was efficientin controlling adult C. hirta plants, when used with sequential application of paraquat and ammonium glufosinate.

Chemical Control of Fleabane Resistant to 2,4-D

Conyza spp. (fleabane) are among the main weeds found globally. They have an annual life cycle and herbaceous size, high seed production, are found in different agricultural environments, such as grain crops (Photo 1). Fleabane control can be hindered by one or more of the following factors: high propagule production, wind propagation of propagules, herbicide resistance. For example, a single fleabane plant can produce more than 200,000 seeds in a year. In Brazil, there are cases of Conyza sumatrensis with multiple resistance to the herbicides chlorimuron and glyphosate, simple resistance to paraquat, in addition to cases of simple or multiple resistance to these and other herbicides (photosystem II inhibitors and synthetic auxins). Also in Paraguay, a country that borders Brazil, there is a report of a biotype with triple resistance to the herbicides paraquat, chlorimuron and glyphosate. In addition to this scenario of difficulties in control and cases of resistance, only 2.7 fleabane plants m–2 can reduce soybean productivity by 50%. These cases of fleabane resistance to herbicides make their management difficult, due to the loss of control tools. One of the main problems in this regard is resistance to 2,4-D, due to the complex rapid necrosis resistance. Rapid necrosis is an uncommon response to 2,4-D herbicide and this response is related to environmental conditions during application (temperature and light). After application of 2,4-D, necrotic symptoms occur rapidly in the leaves, in some situations within less than an hour after application. The rapid accumulation of reactive oxygen species (ROS) after application of 2,4-D causes lipid peroxidation and the production of ROS is related to the occurrence of necrosis in C. sumatrensis. Rapid necrosis resembles a programmed cell death response. However, these symptoms do not lead to plant death, with subsequent plant recovery one to two weeks after application, in addition to disrupting sequential application with burndown herbicides. Considering this setback, alternatives to be used to control fleabane iinclude the use of other synthetic auxins, such as dicamba, triclopyr, halauxifen or fluroxypyr, or even other herbicides, such as atrazine and mesotrione, which are adopted in maize cultivation or in the off-season. These herbicides can be used in the first application in a mixture with glyphosate, in which the control is complemented by the sequential application of glufosinate. These herbicides mixed with glyphosate are believed to be effective in controlling 2,4-D-resistant fleabane in the first application of pre-sowing soybean desiccation. The objective of this study was to evaluate the efficacy of glyphosate in mixtures with dicamba, triclopyr, halauxifen/diclosulam, fluroxypyr/clethodim, 2,4-D or atrazine/mesotrione, with sequential application of glufosinate, in the control of 2,4-D resistant fleabane in soybean pre-sowing.

Integrated Management of Wild Oat (Avena fatua) and Feather Fingergrass (Chloris virgata) Using Simulated Grazing and Herbicides

Wild oat (Avena fatua L.) and feather fingergrass (Chloris virgata Sw.) are among the most problematic weed species in Australian winter and summer cropping systems, respectively. Pot trials were conducted in respective seasons to evaluate the integrated effect of simulated grazing and foliar-applied herbicides on the control of these weed species. Different herbicides were applied 1, 5, and 12 d after grazing on A. fatua plants and 1, 3, 7, 10, and 14 d after grazing on C. virgata. In general, the efficacy of herbicides was better on A. fatua when applied 5 or 12 d after grazing (i.e., 7–20 cm tall plants) and 7 to 14 d (i.e., 10–22 cm tall plants) after grazing on C. virgata. Clethodim 90 g a.i.·ha−1, and haloxyfop 52 and 78 g a.i.·ha−1 resulted in 100% mortality of A. fatua seedlings, irrespective of their application timings. Delayed application (5 or 12 d after grazing) of clethodim 60 g a.i.·ha−1 and pinoxaden 20 and 30 g a.i.·ha−1 resulted in 100% mortality of A. fatua. Glyphosate at the field rate (370 g a.e. ha−1) was the least effective herbicide to control A. fatua plants after grazing. Glufosinate application after grazing resulted in the greatest mortality (69 to 81%) of C. virgata. Depending on application timing, only glufosinate was able to provide complete control of C. virgata seed production. Butroxydim, clethodim, and haloxyfop were found to be promising herbicides to manage C. virgata after grazing but their applications had to be delayed by 7 to 14 d after grazing. This study identified several successful herbicide treatments that could be applied after grazing or mowing for integrated control of A. fatua and C. virgata. However, to achieve complete control of C. virgata, the application of these herbicides needs to be followed by other tools, including additional herbicide applications.

Control of pervasive row crop weeds with dicamba and glufosinate applied alone, mixed, or sequentially

AbstractDicamba and glufosinate are among the few effective postemergence herbicides to control multiple herbicide-resistant weeds in southeastern U.S. cotton and soybean production. Field studies were conducted to determine the effect of weed size and the application of dicamba and glufosinate individually, mixed, or sequentially on common ragweed, goosegrass, large crabgrass, ivyleaf morningglory, Palmer amaranth, and sicklepod control. Sequential herbicide treatments were applied 7 d after the initial treatment. The tested weeds sizes predominantly did not affect weed control. Control of broadleaf weed species with sequential herbicide applications never increased compared to the initial herbicide application. Two applications of glufosinate and/or dicamba + glufosinate controlled grasses better than one application. The order of the herbicides in the sequential applications did not affect broadleaf species control, whereas herbicide order was important for the control of grass weeds. Grass weed control was higher when glufosinate was applied before dicamba. Dicamba + glufosinate additively controlled the weeds, except for goosegrass, for which control was less for dicamba + glufosinate compared to glufosinate alone. The results of the experiment provide evidence that dicamba and glufosinate applied individually, mixed, and sequentially are effective on common row crop weeds found in the southeastern United States, but the species present may dictate how the herbicides are applied together.

Herbicide control of Ambrosia artemisiifolia in sunflower, soybean and maize

Abstract Ambrosia artemisiifolia L. (Asteraceae) has become a major threat to agriculture in many parts of the world. Global agriculture relies on the use of herbicides against A. artemisiifolia in the crops most at risk – sunflower, maize and soybean. This paper aims to provide an overview of the chemical control of A. artemisiifolia and to summarize the latest knowledge in this field. The sunflower is the crop most threatened by A. artemisiifolia, as both plants belong to the same family. The best control level was achieved after the preemergence application of flurochloridone and the combination of dimethenamid-P + pendimethalin. The introduction of the non-GM Clearfield and ExpressSun technologies allowed effective control with postemergence herbicides in sunflower varieties tolerant to imidazolinone and tribenuron-methyl herbicides. In soybean, the highest efficacy was observed in trials with imazamox and bentazone alone and in combination. The combination of imazamox with bentazone had a positive effect on yield compared to untreated stands. The introduction of transgenic soybeans tolerant to glyphosate led to increased glyphosate use and the predictable emergence of weed resistance in America in 1996. Preplant followed by postemergence herbicides were critical for the effective control of glyphosate-resistant A. artemisiifolia in glufosinate tolerant soybean. In maize, the highest efficacy was obtained after the application of glufosinate, bromoxynil and mesotrione + atrazine. Of the above substances for the control of A. artemisiifolia in maize, only mesotrione is currently registered in the EU.

Glufosinate and diquat in pre-harvest desiccation of soybean at four phenological stages, and their impact on seed quality

Glufosinate and diquat may have different levels of efficacy in the pre-harvest desiccation of soybean (Glycine max (L.) Merr.) plants, and may affect quality of seeds differently, depending on the phenological stage at which they are applied. The objective of this study was to evaluate desiccation with glufosinate and diquat at the phenological stages R6, R7.1, R7.2, and R7.3, and to examine their effects on yield and quality of soybean seeds. The experiment was conducted at two sites in the state of Paraná (PR), Brazil, in the 2020-2021 crop season. A randomized block design was used, treatment groups consisted of application of glufosinate or diquat at R6, R7.1, R7.2, and R7.3, and the control group (without desiccant application). Defoliation, maturity, moisture, yield, and seed quality (vigor and germination) were evaluated. Glufosinate and diquat were effective at desiccation and had a significant effect on defoliation and maturity, with final values ≥ 98.8% and ≥ 99.3% respectively. Treatments can accelerate harvest maturity by approximately 3 d and earlier applications do not necessarily favor this acceleration, most notably in trial 1. However, desiccation at earlier stages reduced seed yield and negatively affected seed quality, with values of only 61.3% and 71.8% of vigor and germination in some situations. The application of glufosinate or diquat was effective in the pre-harvest desiccation of soybean plants, with no differences between the assessed herbicides or phenological stages. The application of glufosinate starting at R7.2 or diquat at R7.3 is ideal to avoid deleterious effects on seed yield. Applications at earlier stages may lead to losses of more than 30% seed yield. The use of diquat or glufosinate before R7.2 may reduce the quality of seeds.

Managing Palmer Amaranth (Amaranthus palmeri) with Sequential Applications of Glufosinate and 2,4-D

Aims: Determine the influence of sequential spray order and role of glufosinate when used in a system with 2,4-D to control Palmer amaranth at two different growth stages.
 Study Design: Randomized complete block design with three replications.
 Place and Duration of Study: A fallow, non-crop field at the Texas A&M AgriLife Research and Extension Center, Lubbock, Texas, during the 2018 and 2019 growing seasons.
 Methodology: Herbicides were applied to 7 to 15 cm and 25 to 30 cm Palmer amaranth with a handheld 1.93m CO2-pressurized backpack calibrated to deliver 140 L ha-1 at 207 kPa. Palmer amaranth control was visually estimated on a scale of 0 (no control) to 100% (complete control) relative to the nontreated control. Palmer amaranth biomass and density were collected 43 and 36 days after the last sequential application for 7 to 15 cm and 25 to 30 cm Palmer amaranth in 2019. Palmer amaranth control, biomass, and density were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at P=.05.
 Results: 2,4-D choline + glyphosate followed by glufosinate provided the greatest level of Palmer amaranth control for both sizes of Palmer amaranth. Overall, Palmer amaranth control was not influenced by sequential application timing. Biomass and density were not significantly different among treatments.
 Conclusion: Sequential application order of glufosinate and 2,4-D was not an important factor for Palmer amaranth control. However, due to 2,4-D label restrictions, applying 2,4-D choline + glyphosate followed by glufosinate may be the best option for maximum efficacy.

Optimizing weed control using dicamba and glufosinate in eligible crop systems

AbstractA field experiment was conducted in 2019 and 2020 that included six site-years and four locations in Arkansas to determine the optimal sequence and timing of dicamba and glufosinate applications when applied alone, sequentially, or in combination to control Palmer amaranth by size: labeled (<10 cm height) and non-labeled (13 to 25 cm height). Single applications of dicamba, glufosinate, and dicamba plus glufosinate (not labeled) resulted in less than 80% Palmer amaranth control, regardless of weed size. The mixture of dicamba plus glufosinate was antagonistic for Palmer amaranth control and percent mortality. Sequential applications, averaged over all time intervals and herbicides, improved the percentage of Palmer amaranth control 11 to 17 percentage points over a single application, regardless of weed size at application 28 d after final application (DAFA). Palmer amaranth control with glufosinate followed by (fb) glufosinate and dicamba fb dicamba, pending weed size, were optimized at intervals of 7 d, and 14 to 21 d, respectively. Because single site of action (SOA) postemergence herbicide systems increase the likelihood of the development of resistant biotypes and are not a best management practice (BMP) in that regard; sequential applications involving both dicamba and glufosinate were more effective. Furthermore, the sequence of application mattered with a preference for applying dicamba first. Dicamba fb glufosinate at a 14-d interval was profit-maximizing and the only herbicide treatment that resulted in 100% weed control when size was <10 cm. For larger weed sizes, economic analysis revealed that dicamba fb dicamba performed better than dicamba fb glufosinate when no penalty was assigned for using a single SOA. This resulted in greater yield loss risk and soil weed seed bank in comparison to timelier weed control with the smaller weed size. Hence, timely weed control and two SOAs to control Palmer amaranth are recommended as BMPs that reduce producer risk.

Cucumber tolerance to glufosinate applied preplant or preemergence

AbstractGeorgia vegetable growers produce more than 27% of the nation’s fresh-market cucumbers. To maximize yields and profit, fields must be weed-free when planting. Limitations with current burndown herbicide options motivated academic, industry, and U.S. Department of Agriculture partners to search for new tools to assist growers. One possibility, glufosinate, controls many common and troublesome weeds, but its influence on cucumber development through residual activity when applied before or at planting is not understood. Thus, four different studies were each conducted two to four times from 2017 to 2020 to determine 1) transplant cucumber response to preplant glufosinate applications as influenced by rate, overhead irrigation, and interval between application and planting; and 2) seeded cucumber response to preemergence (PRE) glufosinate applications as influenced by rate, overhead irrigation, and planting depth. Glufosinate applied at 330, 660, 980, and 1,640 g ai ha−1 the day before transplanting caused 11% to 53% injury on sandy, low organic matter soils. Cucumber vine lengths and plant biomass were reduced up to 28% and 46%, respectively, with the three highest rates. Early-season yield (harvests 1 to 4) noted a 31% to 60% yield loss with glufosinate at 660 to 1,640 g ha−1 with similar trends observed with total yield (11 to 13 harvests). Irrigation (0.75 cm) after application and before transplanting reduced injury to less than 21%, eliminated vine length and biomass suppression except at the highest rate, and eliminated yield loss. Extending the interval between glufosinate application and transplanting from 1 to 4 d was not beneficial, and further extending the interval to 7 d significantly reduced injury half the time. When applied PRE to seeded cucumber and combining the data across locations, glufosinate caused less than 7% injury even at 1,640 g ha−1. Seeded plant vine lengths, biomass, and marketable yield were not influenced by the PRE application, and neither irrigation nor planting depth influenced seeded crop response to glufosinate.

Herbicides in soybean development: productive aspects and physiological quality of seeds

The objective was to evaluate the production components of soybean and the physiological quality of seeds according to the application of subdoses of herbicides at the reproductive stage of healthy plants. The treatments consisted of the application of glyphosate (122.5 g acid equivalent [ae] ha-1), chlorimuron (1.75 g active ingredient [ai] ha-1), 2,4-D (134 g ae ha-1), fomesafen (60 g ai ha-1), glufosinate (55 g ai ha-1), paraquat (35 g ai ha-1), and control (no application). The chlorophyll index, agronomic performance, and physiological quality of seeds were evaluated. Glyphosate, chlorimuron, fomesafen, or glufosinate resulted in an increase in soybean plant height. Chlorimuron increased yield compared to the control. Paraquat or glufosinate, despite the injury, did not reduce yield, but the application of these herbicides is not recommended to stimulate plant development, given the potential for injury. The 2,4-D was the only one that caused a reduction in the physiological quality of soybean seeds.

Glyphosate resistance in junglerice (Echinochloa colona) and alternative herbicide options for its effective control

AbstractControl of glyphosate-resistant (GR) junglerice is a challenging task in eastern Australia. There is limited information on the efficacy and reliability of alternate herbicides for GR populations of junglerice, especially when targeting large plants and when temperatures are high. A series of experiments were conducted to confirm the level of glyphosate resistance in three populations of junglerice and to evaluate the efficacy of alternate herbicides for the control of GR junglerice populations. The LD50 of glyphosate of B17/7, B17/34, and B17/35 populations was found to be 298, 2,260, and 1,715 g ae ha–1, respectively, suggesting that populations B17/34 and B17/35 were highly resistant to glyphosate. Glyphosate efficacy was reduced at high-temperature (35 C day/25 C night) compared with low-temperature conditions (25 C day/15 C night), suggesting that control of susceptible populations may also be reduced if glyphosate is sprayed under hot conditions. Preemergence herbicides dimethenamid-P (1,000 g ai ha–1) and pendimethalin (1,500 g ai ha–1) provided 100% control of GR populations (B17/34 and 17/35). Postemergence herbicides, such as clethodim (60 or 90 g ai ha–1), glufosinate (750 g ai ha–1), haloxyfop (52 or 78 g ai ha–1), and paraquat (400 or 600 g ai ha–1), applied at the four-leaf stage provided 100% control of GR populations. For larger junglerice plants (eight-leaf stage), postemergence applications of paraquat (400 or 600 g ai ha–1) provided greater weed control than clethodim, glufosinate, and haloxyfop. A mixture of either glufosinate or haloxyfop with glyphosate provided poor control of GR junglerice populations compared with application of glufosinate or haloxyfop applied alone. Efficacy of glufosinate and haloxyfop for the control of GR populations decreased when applied in the sequential spray after glyphosate application. This study identified alternative herbicide options for GR junglerice populations that can be used in herbicide rotation programs for sustainable weed management.

Biological effects on Palmer amaranth surviving glufosinate

AbstractPalmer amaranth (Amaranthus palmeri S. Watson) is a difficult weed to manage due to competitive growth, fecundity, and evolved herbicide resistance. Limited information exist on the fecundity of vegetative stage Palmer amaranth surviving glufosinate applied at different timings. In addition, research has not investigated the germination or glufosinate susceptibility of the offspring from these surviving plants. Field experiments were conducted across three locations in 2019 to determine (a) the fecundity of Palmer amaranth plants surviving glufosinate applied at different vegetative growth stages, and (b) if the offspring from the surviving plants exhibited differential germination and susceptibility to glufosinate. Palmer amaranth was treated at three different vegetative sizes (5 cm, 7–10 cm, > 10 cm) and orthogonal combinations of these application timings. The application timings corresponded to early‐, mid‐ and late‐postemergence applications. Palmer amaranth plants surviving the mid‐, late‐, and the mid postemergence followed by late postemergence glufosinate application were fecund. Palmer amaranth plants surviving the mid postemergence followed by late postemergence application produced less seed than the plants surviving the mid postemergence and late postemergence application. Palmer amaranth was controlled with other glufosinate applications resulting in no seed production. Germination was affected across location and glufosinate treatments, but no clear trend/pattern was observed. The offspring from Palmer amaranth plants surviving glufosinate applications were controlled by all glufosinate rates tested. These experiments provide evidence that Palmer amaranth surviving glufosinate in the vegetative stages may remain fecund, but fecundity can vary with application timing. No measurable effect on the offspring germination or susceptibility to glufosinate was apparent.