Single Application Of Glyphosate Research Articles

Comparison of Torching and Glyphosate Applications for Japanese Stiltgrass (Microstegium vimineum) Control

Abstract Trials were conducted over three years to evaluate two torchings, torching followed by glyphosate application, raking followed by glyphosate application, and one or two yearly applications of glyphosate for control of Japanese stiltgrass. A single glyphosate application in fall reduced Japanese stiltgrass cover but the percent cover increased during the following growing season. Either two torchings or two applications of glyphosate per season for three years gave excellent Japanese stiltgrass control but plants recovered the year after treatments ended. Raking away leaf litter in spring increased Japanese stiltgrass cover. Torching followed by a glyphosate application was less effective than 2 applications of glyphosate. Treatments would need to be repeated for over three years to eradicate Japanese stiltgrass from a site. Species used in this study: Japanese stiltgrass, Microstegium vimineum (Trin.) A Camus.

Comparing field-based management approaches for invasive Winter Heliotrope (Petasites pyrenaicus, Asteraceae)

Winter Heliotrope (Petasites pyrenaicus, previously P. fragrans), is a persistent, rhizome-forming species found throughout the Mediterranean region and North Africa and is an Invasive Alien Plant (IAP) in the UK and Ireland. P. pyrenaicus excludes native flora by forming a dense, compact canopy that persists for much of the growing season, and is often found growing in rough ground, riparian areas and along communication routes, incurring significant management costs at sites of conservation interest. Our study describes the first field-based assessment of P. pyrenaicus control treatments, testing 12 physical and/or chemical treatments in replicated 1 m2 plots over four years and one chemical treatment over three years. Treatments focused on understanding phenology and resource allocation to exploit rhizome source-sink relationships in P. pyrenaicus. Multiple-stage glyphosate- and picloram-based treatments reduced leaf canopy cover to zero (%) over time, though no treatment completely eradicated P. pyrenaicus. When designing management strategies, effective P. pyrenaicus control may be achieved by a single annual soil and/or foliar application of picloram at 1.34 kg AE ha-1 in spring, or by a single annual foliar application of glyphosate in spring at 2.16 kg AE ha-1. Control is not improved by the addition of other herbicides or physical treatment methods, underlining the importance of these herbicides for perennial invasive plant management. This work confirms the importance of considering plant phenology, resource allocation and rhizome source-sink relationships, to increase treatment efficacy and reduce the environmental impacts associated with the management of P. pyrenaicus and other invasive, rhizome forming species.

Repeated annual application of glyphosate reduces the abundance and alters the community structure of soil culturable pseudomonads in a temperate grassland

Grasslands include some of the most endangered and less protected ecosystems on the planet, such as the Pampa of South America. In the Flooding Pampa where native grasslands were not replaced by crops, glyphosate is frequently sprayed in late-summer every year to increase winter forage productivity for cattle without knowing the impacts on both aboveground and belowground grassland genetic resources. Here, we evaluated the effect of this practice on the abundance and community structure of members of the genus Pseudomonas, one of the most diverse bacterial taxa of the plant rhizosphere broadly recognized by their benefits on plant growth and protection, and on soil remediation. In a field experiment, we analyzed the impact of a single application or of a repeated annual application during 4 consecutive years of the recommended dose of commercial glyphosate (Glacoxan®, 3 l ha-1 and 1440 g active ingredient ha-1). In a greenhouse experiment, we tested whether exposure of bare soil to either commercially formulated or pure glyphosate has a direct impact on the resident pseudomonas community in the absence of plants. In the field, we found that the repeated annual herbicide application resulted in a reduction in the abundance and a shift in the community structure of culturable pseudomonads, with evidence of an enrichment of glyphosate-metabolizing lineages. On the other hand, a single application of glyphosate to bare soil under greenhouse conditions did not affect the abundance nor the community structure of pseudomonads. Considering that these plant-beneficial bacteria are natural inhabitants of the rhizosphere and that their fitness is promoted by plant root exudates, the observed alterations are most likely associated with the drop in the vegetation cover directly provoked by the effect of glyphosate. For the first time, we report on the consequences that a reiterated glyphosate application has on a diverse soil reservoir of bacteria that contributes to crucial ecosystem functions in a temperate natural grassland under animal production. Our findings strengthen the notion that this agronomical practice has an unavoidable imprint on non-target microorganisms that are relevant components of the plant-soil feedbacks and that may be instrumental for ecosystem restoration. We conclude that it is necessary to develop sustainable management practices to avoid affecting key functional microorganisms and exploit their contributions to society.

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.

Japanese Stiltgrass (Microstegium vimineum) Germination Pattern and its Impact on Control Strategies1

Abstract Field trials were conducted by Virginia Master Naturalists to determine the germination period for Japanese stiltgrass and its impact on timing of postemergence herbicide applications. Germination rates declined from April to June, with no germination seen after mid-June. Glyphosate applications in early May significantly reduced Japanese stiltgrass cover that month, but post-treatment germination resulted in approximately 25% cover by October, with 78% cover seen in untreated plots. However, no Japanese stiltgrass was observed in October when glyphosate was applied in either the third week of June or the third week of July. A single application of glyphosate was effective for Japanese stiltgrass control if applications are made in June after new germination had ceased, verified by multi-year herbicide field trials. Field trials conducted by Virginia Tech showed preemergence applications of prodiamine reduced Japanese stiltgrass stand from 30 to 94%, depending on rate and timing, but even in the most effective treatment there was still at least 19% cover by August. Prodiamine treatments that utilized May applications were more effective for crabgrass (Digitaria spp.) control than for Japanese stiltgrass, supporting the earlier germination pattern for Japanese stiltgrass. Inclusion of this work in this paper provides a more complete picture of the treatment options for Japanese stiltgrass. A timed postemergence herbicide application may be a better control option for this weed than use of a preemergence herbicide application. Index words: herbicide application, invasive plants, weed control. Chemicals used in this study: Glyphosate [N-(phosphonomethyl)glycine)], prodiamine (2,6-Dinitro-N,N-dipropyl-4-(trifluoromethyl)-1,3-benzenediamine). Species used in this study: Japanese stiltgrass (Microstegium vimineum (Trin.) A Camus.).

Late‐Season Bermudagrass Control with Glyphosate, Fluazifop, and Mesotrione Combinations

Core Ideas More information is needed to improve late‐season bermudagrass control strategies in the Central Plains region of the United States. A single autumn application of glyphosate reduces bermudagrass cover the following spring. Bermudagrass control with a single autumn application of glyphosate was not improved by adding fluazifop, mesotrione, or both. Multiple summer applications of glyphosate (N‐(phosphonomethyl)glycine) are commonly recommended for bermudagrass (Cynodon spp.) control. However, this regime results in an extended period of displeasing and nonfunctional turfgrass, and is not ideal for spring establishment. An autumn glyphosate application prior to winter dormancy can control bermudagrass and may benefit spring establishment projects. However, research is needed to more precisely define the parameters of efficacious late‐season herbicide applications for bermudagrass control as it transitions into dormancy. Therefore, our objective was to examine late‐season bermudagrass removal using combinations of glyphosate, fluazifop‐p‐butyl (fluazifop) (Butyl (R)‐2‐[4[[5‐(trifluoromethyl)‐2‐pyridinyl]oxy]phenoxy]propanoate), and mesotrione (2‐(4‐methylsulfonyl‐2‐nitrobenzoyl)‐1,3‐cyclohexanedione). Experiments were initiated in October 2013 at the Rocky Ford Turfgrass Research Center in Manhattan, KS, on mature ‘Midlawn’ hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy], and at Stagg Hill Golf Course in Manhattan, KS, on mature common bermudagrass [C. dactylon (L.) Pers.]. Seven herbicide treatments containing combinations of glyphosate, fluazifop, and mesotrione were evaluated. Green bermudagrass cover (0–100%) was visually estimated when treatments were applied and every 14 d after application. Only treatments containing glyphosate reduced the green cover of bermudagrass at each site the following year. Across all ratings dates and locations, adding mesotrione, fluazifop, or both to glyphosate did not further reduce green bermudagrass cover. Overall, results indicate that a single autumn application of glyphosate prior to bermudagrass dormancy reduces bermudagrass cover the following spring. The significant reduction at spring green‐up may allow turf managers to make additional applications in the spring for increased control before spring establishment.

Weed Suppressive Ability of Cover Crop Mixtures Compared to Repeated Stubble Tillage and Glyphosate Treatments

The utilization of an effective stubble management practice can reduce weed infestation before and in the following main crop. Different strategies can be used, incorporating mechanical, biological, and chemical measures. This study aims at estimating the effects of cover crop (CC) mixtures, various stubble tillage methods, and glyphosate treatments on black-grass, volunteer wheat and total weed infestation. Two experimental trials were conducted in Southwestern Germany including seven weed management treatments: flat soil tillage, deep soil tillage, ploughing, single glyphosate application, dual glyphosate application, and a CC mixture sown in a mulch-till and no-till system. An untreated control treatment without any processing was also included. Weed species were identified and counted once per month from October until December. The CC mixtures achieved a black-grass control efficacy of up to 100%, whereas stubble tillage and the single glyphosate treatment did not reduce the black-grass population, on the contrary it induced an increase of black-grass plants. The dual glyphosate application showed, similar to the CC treatments, best results for total weed and volunteer wheat reduction. The results demonstrated, that well developed CCs have a great ability for weed control and highlight that soil conservation systems do not have to rely on chemical weed control practices.

Weed Control, Environmental Impact, and Net-Profit of Two-Pass Weed Management Strategies in Dicamba-Resistant Soybean (<i>Glycine max</i>) Using Conventional Tillage

Traditional two-pass weed management strategies need to be compared with new strategies in glyphosate/dicamba-resistant soybean. Weed control, soybean yield, partial profitability and environmental impact (EI) were evaluated in glyphosate/dicamba-resistant soybean using dicamba applied alone or in a tank-mix with dimethenamid-P applied preemergence (PRE). Trials were conducted at three locations during 2014 and 2015. Several PRE herbicides provided excellent control of broadleaf and grass weeds. Dicamba provided > 91% control of broadleaf weeds, and the addition of dimethenamid-P improved grass control. All weed species at the trial locations were controlled > 94% following a postemergence (POST) application of glyphosate. Weed interference reduced soybean seed yield 33% where no herbicide was applied. A single POST application of glyphosate had the lowest EI. Several treatments improved early-season weed control and reduced early-season weed density and biomass compared to glyphosate and had similar EI values. In this study, there was no benefit to yield or partial profit by including a PRE herbicide for weed management; however, the inclusion of multiple modes-of-action in a herbicide program may reduce the selection for herbicide-resistant weeds.

Single and Sequential Applications of Anthem Maxx, Solstice, Acuron, Balance Flexx, Corvus, Halex GT, Verdict, Sharpen, Glyphosate, and Atrazine in Irrigated Corn

Single and Sequential Applications of Anthem Maxx, Solstice, Acuron, Balance Flexx, Corvus, Halex GT, Verdict, Sharpen, Glyphosate, and Atrazine in Irrigated Corn

Late Glyphosate Applications Alter Yield and Yield Components in Glyphosate-Resistant Canola (Brassica napus)

The development of glyphosate-resistant canola has provided improved weed-management options for growers, but crop tolerance to glyphosate may be inadequate at later growth stages. In this study, glyphosate-resistant canola 45H28 (RR) was used to determine the effects of glyphosate application timing on yield and yield components at several sites in western Canada. Canola received a single glyphosate applications at the two-leaf, six-leaf, bolting, and early bloom stages and sequential applications at the two-leaf + six-leaf, two-leaf + bolting, and two-leaf + early bloom stages. Contrasts were made between early vs. late, single vs. sequential, and on-label (two to six-leaf stage) vs. off-label (above six-leaf stage). In general, differences between application timings were observed for yield and yield components in 3 of 8 site-yr. Off-label applications of glyphosate (later than six-leaf) significantly decreased yield, seeds per pod, and increased thousand-seed weight and aborted pods in canola at the Lethbridge and St. Albert locations. Increased glyphosate translocation because of adequate, but not excessive, moisture to new growth may have suppressed new seed formation and encouraged pod abortion at the time of application in the 2010 and 2011 seasons. Results from this experiment demonstrate the importance of proper application timing of glyphosate on canola and can help better predict the effects of late applications.

Evaluation of two chemical weed control systems in sugar beet in Germany and the Russian Federation

Roundup Ready® sugar beets are widely grown in the USA since their market introduction in 2005. The system has proven to be cost-efficient and reliable. However, the negative social image among consumers and politicians has prohibited the adoption of this technology in Europe. Seven field experiments were conducted over three years in Germany and the Russian Federation to compare weed control efficacy and sugar beet yields of post-emergent glyphosate applications with conventional selective herbicides. Although weed infestations at the Russian sites were higher than in Germany, weed control efficacies were similar at both locations ranging between 78% and 100%. Glyphosate applications resulted in significantly higher weed control efficacies than the conventional herbicides in four out of 7 experiments. In five experiments, a single glyphosate application gave equal weed control efficacy as two and three glyphosate applications. White sugar yield was always higher in the weed control treatments than in the untreated plots. There was no yield difference between treatments based on glyphosate and conventional herbicide applications in 6 out of 7 experiments. The results demonstrate a slight benefit of the glyphosate-based weed control program compared to the conventional herbicide system in terms of weed control efficacy.

Influence of glyphosate timing on Kochia scoparia demographics in glyphosate-resistant sugar beet

The recent evolution of glyphosate-resistant (GR) Kochia scoparia (kochia) is a potential threat to the sustainability of GR cropping systems, including GR sugar beet in the northwestern United States. The lack of effective and economical, alternative herbicide programs for K. scoparia control in GR sugar beet further exacerbates the problem. Therefore, it is critical to understand the population dynamics and demographics of K. scoparia in response to the glyphosate application timing, and their overall impact on the replenishment of the weed seed bank in the soil, and on GR sugar beet yields. To fulfill this objective, field experiments were conducted at the Montana State University Southern Agricultural Research Center near Huntley, Montana, USA in 2012 and 2013. Glyphosate timing treatments included a single application at the 2-leaf (lf), 6-lf, or 10-lf stage of sugar beet or sequential applications at 2-lf followed by (fb) 6-lf, 6-lf fb 10-lf, 2-lf fb 6-lf fb 10-lf, or 6-lf fb 10-lf fb canopy closure (CC) stage of sugar beet. K. scoparia survival, biomass, and seed production were monitored in three cohorts that emerged at different growth stages of sugar beet during the season. K. scoparia plants in cohort 1 and 2 were more competitive (greater biomass and seed production) than those in cohort 3. Compared with a single glyphosate timing, sequential applications of glyphosate at 6-lf fb 10-lf stages of sugar beet prevented survival, biomass and seed production in cohort 1 and cohort 2. K. scoparia plants in cohort 3 that emerged after the glyphosate application at the 10-lf stage of sugar beet, produced up to 1123 seeds m−2. A follow-up application of glyphosate at the CC stage of sugar beet was needed to prevent biomass and seed production from cohort 3 survivors. Irrespective of timing, sequential applications of glyphosate provided higher root and sucrose yields than the single glyphosate applications in GR sugar beet. Growers should utilize three applications of glyphosate applied sequentially at 6-lf fb 10-lf fb CC stages of sugar beet to prevent season-long K. scoparia interference and seed additions in GR sugar beet.

Water Use Efficiency and Rain Water Productivity of Wheat under Various Tillage-Glyphosate Interactive Systems

Abstract Rainfed wheat is generally grown in rotation with summer fallow in medium to high rainfall zone of Pothwar plateau of Pakistan. The present study was, therefore, conducted to investigate the impact of shallow and deep tillage practices, with and without herbicide (glyphosate) application, on moisture conservation and subsequent wheat yields. The study also aimed to examine the feasibility of substituting intensive shallow tillage with single application of glyphosate. The experiment was laid out in randomized complete block design with three replicates and net plot size of 14 m x 10 m, during 2007 and 2008 at two locations i.e high and medium rainfall. Wheat cultivar “GA-2002” was planted as a test crop. The data showed the superiority of conservation tillage in terms of conservation of moisture and increasing grain yields. Results also elaborated that tillage cannot be completely eliminated for profitable fallow management. However, deep ploughing with moldboard followed by single application of glyphosate proved potential option for substituting shallow tillage carried out during summer (kharif). The additional benefits under this tillage system included saving in fuel, labour and lower depreciation and maintenance costs for tillage machinery in addition to unquantifiable environmental benefits.

Control of yellow and purple nutsedge in elevated CO2 environments with glyphosate and halosulfuron.

Atmospheric concentrations of carbon dioxide (CO2) have significantly increased over the past century and are expected to continue rising in the future. While elevated levels of CO2 will likely result in higher crop yields, weed growth is also highly likely to increase, which could increase the incidence of herbicide resistant biotypes. An experiment was conducted in 2012 to determine the effects of an elevated CO2 environment on glyphosate and halosulfuron efficacy for postemergence control of purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.). Both species of nutsedge where grown in 3.0-L containers under either ambient or elevated (ambient + 200 μmol mol−1) CO2 in open-top field chambers and treated with either 0.5×, 1.0×, or 1.5× of the manufacturer's labeled rate of halosulfuron, glyphosate, or a tank mix of the two herbicides. The growth of both nutsedge species responded positively to elevated CO2, purple nutsedge had increased shoot and root dry weights and yellow nutsedge had increased shoot, root, and tuber dry weights and counts. Few treatment differences were observed among the herbicides at any of the rates tested. At 3 weeks following herbicide application, both purple and yellow nutsedge were adequately controlled by both herbicides and combinations at all rates tested, regardless of CO2 concentration. Based on this study, it is likely that predicted future CO2 levels will have little impact on the efficacy of single applications of halosulfuron or glyphosate for control of purple and yellow nutsedge at the growth stages described here, although scenarios demanding more persistent control efforts remain a question.

Efficacy of Lumax EZ, Atrazine, Acuron, Armezon, Sharpen, Outlook, Verdict, and Prowl H2O in Irrigated Glyphosate-Resistant Corn

All treatments provided statistically superior control of Palmer amaranth compared to the control or a single application of glyphosate. All treatments provided excellent control of all other weed species. Although all herbicide tank mixes elevated corn yield compared to the control, there were no statistically significant differences among herbicides in their ability to do so.

Eficácia de diferentes manejos das plantas daninhas na cultura da soja transgênica

The continued use of glyphosate can select resistant weeds biotypes and tolerant species, suggesting the need to develop new management practices. Thus, the aim of this proposal was to evaluate the effectiveness of different managements in soybean using residual herbicides and post-emergent control of weeds, and observe the possible effects on crop development. The experiment, in the field, was in a randomized block design with four replications and 14 treatments, involving the application of diclosulam (29.4 g ai ha-1) and sulfentrazone (600 g ai ha1) and post emergent glifosato (712 g ai ha-1) and 2,4-D (670 g ai ha-1) in weed desiccation, 14 days before soybean sowing, and treatments with glifosato in soybean stages V2 and V4 (356 g ai ha-1) and glifosato applied at a single time in V2 or V4 (712 g ai ha-1). We noted the importance of applying residual herbicides with glyphosate to weed control plant, and for the development of culture. The addition of the herbicide sulfentrazone diclosulam or desiccation became a single application of glyphosate in the V4 stage of soybean enough.

Effects of single and multiple applications of glyphosate or aminopyralid on simple constructed plant communities.

To determine effects of multiple applications of herbicides on small constructed plant communities, Prunella vulgaris L.var. lanceolata Fern, Festuca roemeri (Pavlick) Alexeev, Clarkia amoena (Lehm.) Nels., and Cynosurus echinatus L. were grown together in small field plots. Plants were treated with glyphosate at target concentrations of 0 × , 0.01 × , 0.1 × , and 0.2× a field application rate (FAR) of 1122 g ha(-1) active ingredient (a.i.) for 3 yr in 1 location, and for 2 yr in a second location. Plants also were treated with aminopyralid at 0 × , 0.037 × , 0.136 × , and 0.5× FAR of 123 g ha(-1) a.i. for 2 yr in 2 locations. Plants received 1, 2, or 3 applications of each herbicide each year. Species and community responses depended on herbicide concentration and number of applications. With glyphosate, plant volume (modified formula for a cone) tended to decrease for all species (especially C. echinatus), and the decreases generally became larger with more applications. Plant communities exposed to the 2 greatest concentrations initially differed from controls but then appeared to recover. With aminopyralid, C. amoena was essentially eliminated from the communities, especially at the 2 greatest FARs, whereas the other 3 species tended to have significant increases in volume, especially at the 2 smallest FARs. With aminopyralid, increasing numbers of applications produced variable results, and the plant community volume never tended to recover.

Johnsongrass (Sorghum halepense) Management as Influenced by Herbicide Selection and Application Timing

Field experiments were conducted in 2009 and 2012 at Fayetteville, AR, to compare four herbicides across three application timings for johnsongrass control and to evaluate the effect of late-season herbicide applications on johnsongrass control, fecundity, seed viability, and progeny emergence. In the first experiment, glyphosate at 840 g ae ha−1and clethodim at 68 and 136 g ai ha−1provided 75 to 94% control of 15- to 60-cm tall johnsongrass and up to 98% stand reduction 4 wk after treatment (WAT). Glufosinate and nicosulfuron were generally effective on ≤30-cm tall johnsongrass; however, efficacy declined as johnsongrass size increased. In the second experiment, glyphosate at 840 g ha−1provided at least 89% johnsongrass control when applied at boot or after panicle emergence and up to 95% stand reduction 3 WAT. Applications of glyphosate at 420 and 840 g ha−1, clethodim at 68 and 136 g ha−1, and glufosinate at 740 g ai ha−1at the boot stage reduced viable seed production of treated plants 94 to 99%. Irrespective of rate, glyphosate and clethodim applied at boot stage reduced progeny emergence by 77 to 95% and 100-seed weight of treated plants 62 to 96% compared to the nontreated check. This research demonstrates the importance of herbicide selection, particularly for controlling johnsongrass plants larger than 30 cm. Additionally, the results demonstrate the benefits of a single application of glyphosate or clethodim at the boot stage of johnsongrass for decreasing the soil seedbank and reducing the success of johnsongrass progeny in future years.

Control of Canada fleabane (<i>Conyza canadensis</i>) with glyphosate DMA/2,4-D choline applications in corn (<i>Zea mays</i>)

Glyphosate resistant (GR) Canada fleabane (horseweed) has quickly spread across southwestern Ontario and is a difficult weed to control in GR crops. Glyphosate dimethylamine (DMA)/2,4-D choline (Enlist Duo?TM Dow AgroSciences LLC), a new herbicide premix developed by Dow Agro Sciences, provides control of GR and other problematic weeds. The objective of this study was to compare single and sequential applications of glyphosate DMA/2,4-D choline for the control of GR Canada fleabane in GR corn. Three single applications of glyphosate (DMA)/2,4-D choline (1720 g·ae·ha-1) were evaluated: 1) preplant (PP) applied to Canada fleabane up to 10 cm diameter/height, 2) postplant 1 (POST 1) applied when Canada fleabane was up to 20 cm tall and 3) postplant 2 (POST 2) applied up to 30 cm tall Canada fleabane. Four sequential applications were also examined:1) PP followed by (fb) POST 1, 2) PP fb POST 2, 3) POST 1 fb POST 2 and 4) PP fb POST 1 fb POST 2. The single applications provided 69%-86% control of the GR Canada fleabane while the sequential applications increased control to 92%-100%. Three applications did not provide an increase in control over a sequential two-pass application at 8 weeks after the application (WAA). Results from this research indicate that a sequential 2-pass application of glyphosate DMA/2,4-D choline provided acceptable control of GR Canada fleabane in corn.

Two-Pass Weed Management with Preemergence and Postemergence Herbicides in Glyphosate-Resistant Soybean

There is little information on the efficacy and profitability of two-pass weed control strategies in soybean when a preemergence (PRE) residual herbicide is followed by glyphosate applied late postemergence (LPOST) under Ontario, Canada environmental conditions. Ten field trials were conducted during 2011-2013 in Ontario, Canada to determine the level of weed control, yield and net returns of various preemergence/postemergence programs in glyphosate-resistant soybean. Crop injury was 2% or less with the herbicides evaluated except for chlorimuron + flumioxazin (PRE) and pyroxasulfone + flumioxazin (PRE) which caused 4% and 7% visible injury in soybean, respectively. A single application of glyphosate resulted in variable weed control (73% - 98%) while the sequential application of glyphosate provided excellent weed control (98% - 100%). The control of all weeds 8 WAA after the LPOST glyphosate application was equivalent regardless of the PRE herbicide applied (96% - 100%). Soybean yield was equivalent to the weed free control regardless of the PRE herbicide applied. Soybean yield was lower than the sequential application of glyphosate with chlorimuron or pyroxasulfone/flumioxazin PRE fb glyphosate LPOST. Generally net return with the two-pass programs was equivalent to the sequential application of glyphosate. Net returns were lower than the sequential application of glyphosate with chlorimuron or s-metolachlor + flumetsulam followed by glyphosate LPOST. Based on these results, a sequential application of glyphosate or a two-pass program of a preemergence residual herbicide followed by glyphosate LPOST are the preferred weed management programs in glyphosate-resistant soybean. The two-pass programs have the potential to reduce selection pressure for glyphosate-resistant weeds.