Applications Of Glufosinate Research Articles

Photosynthetic index and nitrogen assimilation in rapeseed seedlings transplanted in soil with ammonium glufosinate

ABSTRACT: Herbicide application is an effective weed control method for mitigating crop yield loss; however, herbicide overuse can cause toxicity in non-target plants. The present study evaluated the effects of glufosinate at recommended dose for agricultural application (0.45 kg ha-1) and at overuse dose (0.90 kg ha-1) glufosinate application on photosynthetic performance and nitrogen assimilation of the rapeseed varieties D148 and Zhongshuang 11 (ZS11). Both glufosinate concentrations significantly decreased the content of chlorophyll and nitrogenous compounds, except free proline, and the activity of glutamine synthetase and glutamate synthase, and increased the activity of glutamic acid dehydrogenase in both varieties. When the concentration of glyphosate was 0.45kg ha-1, the nitrogen assimilation of the two varieties decreased, which indicated that the recommended dosage inhibited the nitrogen assimilation of the two varieties; however, the increase of net photosynthetic rate of D148 and the decrease of that of ZS11 mean that D148 is more tolerant to the recommended dose of glyphosate than ZS11. The 0.90 kg ha-1 dosage was toxic to both rapeseed varieties. Overall, our results indicated that herbicide overuse inhibited the photosynthetic rate and nitrogen assimilation in rapeseed seedlings, and it is essential to apply a suitable glufosinate dose based on the variety grown to minimize adverse effects on crops and environment.

Evaluation of Seed Treatment, Herbicide, and Nematicide on Tobacco Thrips (Thysanoptera: Thripdae) and Reniform Nematode (Tylenchida: Hoplolaimidae) Control

Numerous pests infest cotton early in the season. Some economically important are Palmer amaranth, Amaranthus palmeri (S. Wats); tobacco thrips, Frankliniella fusca (Hinds); and reniform nematode, Rotylenchulus reniformis (Linford and Oliveira). Thrips and weed management are essential to prevent delayed maturity and reduced crop yield. A field study was conducted during 2015 and 2016 to evaluate the influence of insecticide seed treatment, herbicide, and nematicide on tobacco thrips and reniform nematode control, as well as the impact on cotton growth, development, and yield. Treatments consisted of insecticide seed treatment (insecticide seed treatment and fungicide only), herbicide application (S-metolachlor, glufosinate, S-metolachlor plus glufosinate, and no herbicide), and nematicide application (1, 3-dichloropropene and no nematicide). There were no significant interactions between insecticide seed treatment, herbicide, and nematicide for any parameter. Nor were there any interactions in respect to nematode densities, thrips densities, thrips injury, herbicide injury, or plant biomass. Nematode densities were reduced with the use of 1,3-dichloropropene when sampled at first square and post-harvest. Thrips densities and injury were reduced at the 1- to 2-leaf stage sample timing with an insecticide seed treatment, but not at the 3- to 4-leaf stage sample timing. Herbicide injury was the greatest following S-metolachlor plus glufosinate applications (< 12%). A significant interaction between nematicide and insecticide seed treatment was observed for cotton yield, where the use of 1,3-dichloropropene and the insecticide seed treatment resulted in greater yields than all other treatments.

Control of Conyza spp. with sequential application of glufosinate in soybean pre-sowing

ABSTRACT: Conyza spp. is among the main weeds reported worldwide. Due to its aggressiveness, such as high seed production and dispersion, and the growing reports of biotypes resistant to glyphosate, paraquat, and other herbicides, different control practices are required. Thus, this study aimed to evaluate the efficacy of herbicides with sequential application of glufosinate in soybean pre-sowing for control of Conyza spp. with indicative of resistant to paraquat. The study was carried out in the field, at Assis Chateaubriand and Palotina, state of Paraná, Brazil, in the 2018/19 season. The experiments were conducted in a randomized block design with four replications. The treatments consisted in application of glyphosate, 2,4-D, saflufenacil, glufosinate, saflufenacil/imazethapyr, diclosulam, paraquat/diuron, paraquat and imazethapyr/flumioxazin, at different combinations, in soybean pre-sowing. Control of Conyza spp., crop injury to soybean plants and variables related to agronomic performance (plant height and yield) were evaluated. All treatments were selective for soybean, which showed stronger crop injury in the presence of diclosulam herbicide, but this did not compromise soybean agronomic performance. In general, control levels were high for the treatments used. Except for paraquat treatments, in the area with the highest frequency of Conyza spp. with indicative of resistant to paraquat, and imazethapyr/flumioxazin treatment in both areas. These control results emphasized the importance of glufosinate in this management system and showed promising results for saflufenacil/imazethapyr.

Seed germination ecology of Bidens pilosa and its implications for weed management

It is now widely recognized that Bidens pilosa has become a problematic broadleaf weed in many ecosystems across the world and, particularly in the light of recent climate change conditions, closer management strategies are required to curtail its impact on agricultural cropping. In this investigation, experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of B. pilosa, and also on the response of this weed to commonly available post-emergence herbicides in Australia. The environmental factors of particular interest to this current work were the effect of light and temperature, salinity, burial depth and moisture on B. pilosa since these are key management issues in Australian agriculture. In addition, the effects of a number of commonly used herbicides were examined, because of concerns regarding emerging herbicide resistance. In the tested light/dark regimes, germination was found to be higher at fluctuating day/night temperatures of 25/15 °C and 30/20 °C (92–93%) than at 35/25 °C (79%), whilst across the different temperature ranges, germination was higher in the light/dark regime (79–93%) than in complete darkness (22–38%). The standard five-minute temperature pretreatment required for 50% inhibition of maximum germination was found to be 160 °C, and it was further shown that no seeds germinated at temperatures higher than 240 °C. With regard to salinity, some B. pilosa seeds germinated (3%) in 200 mM sodium chloride (NaCl) but all failed to germinate at 250 mM NaCl. Germination declined from 89% to 2% as the external osmotic potential decreased from 0 to −0.6 MPa, and germination ceased at −0.8 MPa. Seeding emergence of B. pilosa was maximum (71%) for seeds placed on the soil surface and it was found that no seedlings emerged from a depth of 8 cm or greater. A depth of 3.75 cm was required to inhibit the seeds to 50% of the maximum emergence. In this study, application of glufosinate, glyphosate and paraquat provided commercially acceptable control levels (generally accepted as >90%) when applied at the four-leaf stage of B. pilosa. However, none of the herbicide treatments involved in this study provided this level of control when applied at the six-leaf stage. In summary, B. pilosa germination has been clearly shown to be stimulated by light and thus its emergence was greatest from the soil surface. This suggests that infestation from this weed will remain as a problem in no-till conservation agriculture systems, the use of which is increasing now throughout the world. It is intended that information generated from this study be used to develop more effective integrated management programs for B. pilosa and similar weeds in commercial agricultural environments which are tending toward conservation approaches.

Evaluation of herbicides for hair fescue (Festuca filiformis) management and potential seedbank reduction in lowbush blueberry

AbstractHair fescue is a widespread, seed-limited perennial grass in lowbush blueberry fields. Growers rely on pronamide, an expensive and difficult herbicide to use, for hair fescue management. Recent herbicide registrations provide opportunity to reduce pronamide use, though effects of these herbicides on hair fescue suppression and seedbank reduction are not well understood. The objectives of this research were to determine (1) the effects of herbicides currently registered in lowbush blueberry on suppression of hair fescue tufts and (2) whether suppression of hair fescue with these herbicides reduces hair fescue seedbanks. Pronamide gave the most consistent reductions in flowering tuft density, though applications after both autumn pruning and autumn of the nonbearing year were required to reduce the hair fescue seedbank by >60% across sites. Nonbearing-year hexazinone applications did not control hair fescue or reduce the seedbank. Nonbearing-year terbacil applications reduced flowering tuft density, but hair fescue recovered in the bearing year, and the seedbank was not reduced. Glufosinate applications following autumn pruning or in the spring of the nonbearing year did not suppress hair fescue or reduce the seedbank. Spring nonbearing-year foramsulfuron applications, alone or after autumn or spring glufosinate applications, reduced hair fescue flowering tuft density, but hair fescue recovered in the bearing year, and the seedbank was not reduced. In contrast, autumn and spring glufosinate applications followed by spring nonbearing-year foramsulfuron applications, when combined with autumn nonbearing-year pronamide applications, reduced flowering tuft density in both the nonbearing and bearing years and reduced the hair fescue seedbank by 58% to 83% across sites. Results indicate that hair fescue seedbanks can be reduced in lowbush blueberry fields and that a reduction in pronamide use will require alternative bearing-year treatments to prevent tuft recovery and seed production.

Evaluation of broadcast and spot herbicide applications for narrowleaf goldenrod [Euthamia graminifolia (L.) Nutt.] management in lowbush blueberry

AbstractGoldenrods are common perennial weeds in lowbush blueberry fields in Nova Scotia. Management options are limited to mowing and suppression with POST mesotrione applications. The objectives of this research were to (1) compare efficacy of single versus sequential nonbearing-year POST mesotrione applications on goldenrod (2) identify the optimal interval between sequential POST mesotrione applications (3) evaluate nonbearing-year POST bicyclopyrone applications on goldenrod, and (4) evaluate nonbearing-year summer and fall herbicide spot treatments on goldenrod. POST mesotrione applications at 144 g ai ha−1 caused 39% to 77% injury but did not reduce goldenrod shoot density. In contrast, mesotrione applications at 144 g ai ha−1 followed by sequential mesotrione application at 14, 21, or 28 days after initial treatment caused greater than 90% injury to goldenrod and reduced both nonbearing- and bearing-year shoot density. POST bicyclopyrone applications at 50 g ai ha−1 caused 69% to 80% injury to goldenrod but did not reduce shoot density. A bicyclopyrone plus mesotrione tank mixture did not improve goldenrod control relative to mesotrione or bicyclopyrone alone. Summer spot applications of glyphosate (7.24 g ae L water−1), glufosinate (0.75 g ai L water−1), and mesotrione (0.72 g ai L water−1) consistently injured goldenrod and reduced both nonbearing- and bearing-year shoot density. Summer spot applications of bicyclopyrone (0.25 g ai L water−1), flazasulfuron (0.31 g ai L water−1), dicamba (1 g ae L water−1), dicamba plus diflufenzopyr (0.7 g ae L water−1 plus 0.3 g ai L water−1), triclopyr (1.68 g ai L water−1), clopyralid (0.08 g ai L water−1), tribenuron methyl (0.2 g ai L water−1), and foramsulfuron (0.2 g ai L water−1) injured goldenrod but did not consistently reduce shoot density. When these herbicides were evaluated as fall spot applications, only glyphosate reduced goldenrod shoot density in the year after application.

Utility of glufosinate in postemergence row middle weed control in Florida plasticulture production

AbstractHerbicides are the foundation for row-middle weed control in Florida plasticulture production. Paraquat is commonly used as a burndown herbicide, and resistance issues have subsequently developed. Halosulfuron is mixed with PRE and POST herbicides to provide additional control of nutsedge. The objective of the study was to determine glufosinate efficacy on weeds emerging in the row-middle and suitability in mixture with halosulfuron for nutsedge control. For total weed control, the high dose of glufosinate (983 g ai ha–1) gave the highest overall control (98% and 64% at 4 wk after treatment for experiments 1 and 2, respectively), and the low rate of glufosinate (656 g ha–1) (67% and 39%) gave results comparable to paraquat (57% and 44%). The high glufosinate dose and paraquat gave comparable control of Brazil pusley (74% to 77% control). Glufosinate + halosulfuron mixture had lower efficacy on Brazil pusley than halosulfuron + paraquat mixture. Glufosinate application reduced grass densities, whereas paraquat did not. Increasing the glufosinate dose did not further decrease grass densities. Similar trends in grass control were also demonstrated in their respective mixtures. Mixing halosulfuron with glufosinate or paraquat did not provide consistent reductions in nutsedge densities, nor did adding paraquat or glufosinate further reduce densities compared with halosulfuron alone for the 4-wk study period. Both paraquat and glufosinate antagonized halosulfuron and reduced efficacy on nutsedge. Compared to controls, there was a reduction between expected and actual nutsedge control for paraquat and glufosinate (25% and 36%), respectively. For total weed control, glufosinate is a suitable alternative to paraquat for row-middle weed management in vegetable production.

Barnyardgrass (Echinochloa crus-galli) Control as Affected by Application Timing of Glufosinate Applied Alone or Mixed with Graminicides

AbstractField and greenhouse studies were conducted to evaluate the antagonism potential of glufosinate applied sequentially or mixed with graminicides on barnyardgrass control. Applications of glufosinate alone provided variable control throughout the growing season in both field and greenhouse experiments. In the field, barnyardgrass control was not adversely affected by glufosinate- and clethodim-mix applications or sequential applications of glufosinate before or after clethodim. Soybean yield was not affected by application timing or clethodim rate, with yield ranging from 1,748 to 2,733 kg ha−1. In the greenhouse, glufosinate applied 1 and 3 d before graminicides generally reduced barnyardgrass control compared with the graminicides applied alone. The response with quizalofop-P was not as dramatic as with the other graminicides. Although significant visual barnyardgrass control differences were detected due to application timing of glufosinate, barnyardgrass biomass with fluazifop-P and quizalofop-P did not differ between the application timings of glufosinate. However, glufosinate applied 1 and 3 d before clethodim had significantly greater biomass compared with glufosinate applied 1 and 3 d after clethodim. The differences in environmental conditions and growth stages at the time of application may have contributed to barnyardgrass control response differences between the field and greenhouse experiments. Although barnyardgrass control in the field was not affected by glufosinate application timing, data from the greenhouse indicate potential exists for reduced control if glufosinate is applied 1 or 3 d before graminicides.

LibertyLink®, WideStrike® and XtendFlex® Tolerance to Late Postemergence Applications of Glufosinate and S-Metolachlor

Glufosinate remains an important postemergence (POST) herbicide for controlling glyphosate-resistant Amaranthus palmeri (S. Wats) in auxin-tolerant trait systems. Although visual injury from glufosinate applications to WideStrike cultivars is expected, concerns have been raised on the visual injury noted in XtendFlex cultivars, particularly with sequential late-POST glufosinate applications or when S-metolachlor is tank-mixed with glufosinate. Field trials were established in Jackson, TN during 2015 and 2017 and in Huntersville, TN during 2016. Herbicide treatments included an untreated; one, two, and three sequential applications of glufosinate; and glufosinate + S-metolachlor followed by (FB) glufosinate FB glufosinate + S-metolachlor. Applications began 40 days after planting and sequential applications were made every 10 to 14 days. Cultivars included DP 1522 B2XF (DeltaPine, Bayer CropScience, St. Louis, MO), PHY 333 WRF (Phytogen, Corteva Agriscience, Indianapolis, IN), and ST 4946 GLB2 (Stoneville, BASF Corp., Florham Park, NJ). Visual injury ratings varied across timing, treatment, cultivar, and site-year. Three sequential applications of glufosinate with two applications of S-metolachlor caused 7 to 20%, 2 to 15%, and 1 to 8% injury 10 days after the last application in PHY 333 WRF, DP 1522 B2XF, and ST 4946 GLB2, respectively. Cultivar lint yield and fiber quality did not vary by herbicide treatment. Producers who apply glufosinate should expect increasing visual injury from LibertyLink to XtendFlex to WideStrike cultivars, with a sharp increase in visual injury from XtendFlex to WideStrike cultivars; however, sequential, labeled applications of glufosinate with or without two applications of S-metolachlor will likely not impact yields of LibertyLink, WideStrike, or XtendFlex cultivars.

Ammonium Glufosinate Associated with Post-Emergence Herbicides in Corn with the cp4-epsps and Pat Genes

ABSTRACT: With the possibility of using ammonium glufosinate in corn, studies on its association with other herbicides are essential. The aim of this study was to assess weed control and herbicide selectivity in association with ammonium glufosinate in corn containing the pat and cp4-epsps genes. The experiment was carried out under field conditions in two sites in a randomized block design with four replications. Treatments consisted of ammonium glufosinate, glyphosate, ammonium glufosinate + glyphosate, ammonium glufosinate + nicosulfuron, ammonium glufosinate + atrazine, ammonium glufosinate + tembotrione, ammonium glufosinate + mesotrione, ammonium glufosinate + carfentrazone ethyl, ammonium glufosinate + bentazon, ammonium glufosinate + 2,4-D, control without weeding, and hand-weeded control. Visual assessments were performed regarding damage, electron transport rate in photosystem II (ETR), ammonia quantification, height, and grain yield of corn plants, as well as weed control at both sites. The application of ammonium glufosinate and its associations did not provide a reduction in productivity when compared to the hand-weeded control. Some treatments presented higher levels of visual damage and ammonia accumulation, but without a yield reduction. Therefore, herbicide mixture with ammonium glufosinate may be an alternative to weed control without damaging corn crop, which presents in its genetic constitution the cp4-epsps and pat genes.

Lack of effects of glyphosate and glufosinate on growth, mineral content, and yield of glyphosate- and glufosinate-resistant maize

ABSTRACTWhether herbicides used in transgenic, herbicide-resistant crops have negative effects on those crops has been controversial. Most all of the data on this topic has been on glyphosate-resistant (GR) soybean, with little information available on GR and glufosinate-resistant (GluR) maize. A GR plus GluR maize variety was evaluated in the greenhouse and the field for effects of glyphosate and glufosinate on growth, mineral content, and yield. Treatments were: 1) a herbicide-free control; 2) 980 g acid equivalent (a.e.) ha−1 glyphosate at 21 days after emergence (DAE); 3) 600 g active ingredient (a.i.) ha−1 glufosinate at 21 DAE; 4) sequential applications of glyphosate at 520 and 980 g a.e. ha−1 at 14 and 28 DAE, respectively; 5) sequential applications of glufosinate at 300 and 300 g a.i. ha−1 at 14 and 28 DAE, respectively; and 6) sequential application of glyphosate (980 g a.e. ha−1) and glufosinate (600 g a.i. ha−1) at 14 and 28 DAE, respectively. None of the herbicide treatments affected plant growth, yield, or content of N, P, K, Ca, Mg, S, Mn, Fe, Cu, or Zn in the greenhouse or field. In grain of field-grown plants, no glufosinate was found and glyphosate (0.12 ng g−1) was only found in the sequential glyphosate treatment.

Management Programs to Control Conyza spp. in Pre-Soybean Sowing Applications

ABSTRACT: The goal of this study was to compare the efficacy of different weed management through a burndown application followed by sequential applications of herbicides to control Conyza spp. Thus, four field experiments were conducted, two in the western region of Paraná state (E1 and E2), one in Jataí, Goiás state (E3) and another one in Ibirubá, Rio Grande do Sul state (E4). Conyza spp. in this area had a height ranging between 25 and 60 cm. Treatments were arranged in a randomized block design with four replications. The primary herbicide treatments were 2,4-D + glyphosate + diclosulam, chlorimuron-ethyl + glyphosate + 2,4-D, and four doses of diclosulam + halauxifen-methyl + glyphosate. These treatments were applied singly or in sequential applications, made 10 days before the application of ammonium glufosinate, paraquat or saflufenacil. In all experiments, results showed efficient (90%) control of treatments containing diclosulam + halauxifen-methyl in combination with glyphosate on day 35 DAA, regardless of sequential applications. Applications of 2,4-D + glyphosate + diclosulam or chlorimuron-ethyl + glyphosate + 2,4-D were not effective against Conyza spp. at E1 and E2 locations, possibly due to the greater weed size (50 to 60 cm) at these sites. However, the same treatments were effective at E3 and E4 locations, where weeds were smaller. Diclosulam + halauxifen-methyl + glyphosate associated with ammonium glufosinate, paraquat or saflufenacil in sequential applications, proved to be an important tool to manage Conyza spp. at different growth stages.

PRODUTIVIDADE, QUALIDADE FISIOLÓGICA E RESÍDUO EM SEMENTES DE TRIGO EM FUNÇÃO DA DESSECAÇÃO COM HERBICIDAS

In the wheat crop,pre-harvest desiccation with herbicides caninfluencethe productivity and physiological seed quality.The study aimed to quantify the yield, physiological seed quality,andresidue in wheat seeds.The experimental design was a randomized block designina 2x2x6 factorial, being thefactor A constituting of wheat cultivars (BRS 177 e BRS Umbu),the factor B application stages (before and after physiological maturation) and, factor C desiccation with different herbicides (2,4-D, paraquat, glyphosate, ammonium glufosinate, metsulfuron-methyl, and control) with four replications.The variables analyzed were thethousand seedsweight, hectoliter weight, number of antheciumper spike, seed yield, physiological seed quality by the vigortestsand standard germination, and residue in wheat seeds after the application of herbicides in pre-harvest.The desiccation in pre-harvest herbicide held at a later stage after physiological maturity, in general, does not affect the physiological quality and seed yield of BRS Umbu and BRS 177 cultivars. The application of methyl-metsulfuronand paraquat does not show residual effects on the seed independent of the application stage, while the application of ammonium glufosinate, glyphosate, and 2,4-D,when applied before the physiological maturity result residue levels in wheat seed.

Spray droplet size and carrier volume effect on dicamba and glufosinate efficacy.

Pesticide applications using a specific droplet size and carrier volume could maximize herbicide efficacy while mitigating particle drift in a precise and efficient manner. The objectives of this study were to investigate the influence of spray droplet size and carrier volume on dicamba and glufosinate efficacy, and to determine the plausibility of droplet-size based site-specific weed management strategies. Generally, across herbicides and carrier volumes, as droplet size increased, weed control decreased. Increased carrier volume (187 L ha-1 ) buffered this droplet size effect, thus greater droplet sizes could be used to mitigate drift potential while maintaining sufficient levels of weed control. To mitigate drift potential and achieve satisfactory weed control (≥ 90% of maximum observed control), a 900 µm (Ultra Coarse) droplet size paired with 187 L ha-1 carrier volume is recommended for dicamba applications and a 605 µm (Extremely Coarse) droplet size across carrier volumes is recommended for glufosinate applications. Although general droplet size recommendations were created, optimum droplet sizes for weed control varied significantly across site-years. Convoluted interactions occur between droplet size, carrier volume, and other application parameters. Recommendations for optimizing herbicide applications based on droplet size should be based on a site-specific management approach to better account for these interactions. © 2018 Society of Chemical Industry.

The effects of glyphosate, glufosinate, paraquat and paraquat-diquat on soil microbial activity and bacterial, archaeal and nematode diversity

In this study, we investigated the effects of one-off applications of glyphosate, glufosinate, paraquat, and paraquat-diquat on soil microbial diversity and function. All herbicides were added to soil as pure compounds at recommended dose and were incubated under laboratory conditions for 60 days. High-throughput phylogenetic marker gene sequencing revealed that none of the herbicides significantly influenced the richness, evenness and composition of bacterial and archaeal communities. Likewise, the diversity, composition and size of nematode communities were not significantly influenced by any of the herbicides. From a functional perspective, herbicides did not significantly affect fluorescein diacetate hydrolysis (FDA) and beta-glucosidase activities. Furthermore, the ability of soil organisms to utilise 15 substrates was generally unaffected by herbicide application. The only exception to this was a temporary impairment in the ability of soil organisms to utilise three organic acids and an amino acid. Given the global and frequent use of these herbicides, it is important that future studies evaluate their potential impacts on microbial communities in a wider-range of soils and environmental conditions.

Interaction of Glufosinate and <i>Colletotrichum truncatum</i> on Ammonia Levels and Glutamine Synthetase Activity in Hemp Sesbania

The use of microbes and microbial products as bioherbicides has been studied for several decades, and combinations of bioherbicides and herbicides have been examined to discover possible synergistic interactions to improve weed control efficacy. Bioassays were conducted to assess possible interactions of the herbicide glufosinate [2-amino-4-(hydroxymethylphosphinyl) butanoic acid] and Colletotrichum truncatum (CT), a fungal bioherbicide to control hemp sesbania (Sesbania exaltata)]. Glufosinate acts as a glutamine synthetase (GS) inhibitor that causes elevated ammonia levels, but the mode of action of CT is unknown. GS has also been implicated in plant defense in certain plant-pathogen interactions. The effects of spray applications of glufosinate (1.0 mM) orbioherbicide (8.0 × 104 conidia ml-1), applied alone or in combination were monitored (88 h time-course) on seedling growth, GS activity and ammonia levels in hypocotyl tissues under controlled environmental conditions. Growth (elongation and fresh weight) and extractable GS activity were inhibited in tissues by glufosinate and glufosinate plus CT treatments as early as 16 h, but CT treatment did not cause substantial growth reduction or GS inhibition until after ~40 h. Generally, ammonia levels in hemp sesbania tissues under these various treatments were inversely correlated with GS activity. Localization of hemp sesbania GS activity on electrophoretic gels indicated a lack of activity after 30 h in glufosinate and glufosinate plus CT-treated tissue. Untreated control tissues contained much lower ammonia levels at 24, 64, and 88 h after treatment than treatments with CT, glufosinate or their combination. CT alone caused elevated ammonia levels only after 64 - 88 h. Glufosinate incorporated in agar at 0.25 mM to 2.0 mM, caused a 10% - 45% reduction of CT colony radial growth, compared to fungal growth on agar without glufosinate, and the herbicide also inhibited sporulation of CT. Although no synergistic interactions were found in the combinations of CT and glufosinate at the concentrations used, further insight on the biochemical action of CT and its interactions with this herbicide on hemp sesbania was achieved.

Effect of Late-Season Herbicide Applications on Inflorescence and Seed Production of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida)

Giant ragweed is one of the most competitive annual broadleaf weeds in corn and soybean crop production systems in the United States and eastern Canada. Management of giant ragweed has become difficult due to the evolution of resistance to glyphosate and/or acetolactate synthase (ALS)-inhibitor herbicides and giant ragweed’s ability to emerge late in the season, specifically in the eastern Corn Belt. Late-season herbicide application may reduce seed production of weed species; however, information is not available about late-season herbicide applications on giant ragweed seed production. The objective of this study was to evaluate the effect of single or sequential late-season applications of 2,4-D, dicamba, glyphosate, and glufosinate on inflorescence injury and seed production of glyphosate-resistant (GR) giant ragweed under greenhouse and field conditions (bare ground study). Single and sequential applications of glufosinate resulted in as much as 59 and 60% injury to giant ragweed inflorescence and as much as 78 and 75% reduction in seed production, respectively, under field and greenhouse conditions. In contrast, single or sequential applications of 2,4-D or dicamba resulted in ≥ 96% inflorescence injury and reduction in seed production in the field as well as in greenhouse studies. The results indicated that 2,4-D or dicamba are effective options for reducing seed production of glyphosate-resistant giant ragweed even if applied late in the season. Targeting weed seed production to decrease the soil seedbank will potentially be an effective strategy for an integrated management of GR giant ragweed.

CHEMICAL OPTIONS FOR THE CONTROL OF SILVERLEAF NIGHTSHADE (Solanum elaeagnifolium)

ABSTRACT Silverleaf nightshade is a difficult-to-control perennial weed. Field experiments were conducted in northern Greece to evaluate the control of silverleaf nightshade with POST applications of glufosinate (1,500 g a.i. ha-1), glyphosate (3,600 g a.i. ha-1), tembotrione (148.5 g a.i. ha-1), and a mixture of tembotrione plus bentazon (148.5 plus 1,440 g a.i. ha-1) at an early vegetative stage (plant height 10-15 cm) and at the beginning of flowering (plant height 30-50 cm). Glufosinate provided > 95% control of silverleaf nightshade from 7 to 39 days after treatment (DAT), regardless of the vegetative stage at herbicide application. Similarly, glyphosate provided up to 90% control around 39 DAT at either growth stage applied, exhibiting gradually increasing efficacy. Tembotrione alone controlled silverleaf nightshade 85% when applied at the early vegetative stage and 48% when applied at the beginning of flowering. The mixture of tembotrione plus bentazon applied at the beginning of flowering exhibited 74% control at 21 DAT; however, the control was decreased to 41% at 35 DAT. When the mixture was applied at the early vegetative stage, S. elaeagnifolium control was 61% at 23 DAT, which was decreased to 27% at 39 DAT. Glufosinate and glyphosate were found to be reliable options for control of silverleaf nightshade when applied at either weed growth stage; tembotrione could be also another reliable option, however, when applied only at an early vegetative stage. The results have significant implications for developing appropriate management practices for silverleaf nightshade, taking into account chemical options for preventing the evolution of herbicide resistance.

EnlistTMWeed Control Systems for Palmer Amaranth (Amaranthus palmeri) Management in Texas High Plains Cotton

Weed management systems were established near Lubbock, TX in 2013, 2014, and 2015 to assess the effectiveness of premixed 2,4-D choline+glyphosate alone and in combination with glufosinate and soil-residual herbicides for Palmer amaranth control. Systems consisted of trifluralin applied preplant incorporated followed by an early POST application followed by a mid-POST application. Palmer amaranth control 21 days after the early POST application ranged from 75 to 90% for all treatments that included 2,4-D choline+glyphosate alone or in a tank-mixture in 2013. Twenty-eight days after the mid-POST application, Palmer amaranth was controlled 86 to 99% for all herbicide systems with the exception of systems that included a mid-POST application of glufosinate alone. Combined across 2014 and 2015, Palmer amaranth control 21 days after the early POST application ranged from 96 to 98% for all systems that included 2,4-D choline+glyphosate, 2,4-D choline alone, or 2,4-D choline in a tank-mixture. Combined across 2014 and 2015, Palmer amaranth control 28 days after the mid-POST application ranged from 95 to 100% with the exception of the following: trifluralin preplant incorporated followed by glufosinate with or without acetochlor applied early POST followed by glufosinate mid-POST and trifluralin preplant incorporated followed by glyphosate early POST followed by glyphosate mid-POST. Overall, numerous effective systems were identified; however, systems containing 2,4-D choline+glyphosate or 2,4-D choline early POST and/or mid-POST were among the most effective. Glyphosate or glufosinate only systems or systems that relied on glufosinate alone at the mid-POST timing were inconsistent and often performed poorly.

Susceptibility of American burnweed (Erechtities hieraciifolius) to herbicides and clipping in wild blueberry (Vaccinium angustifolium Ait.)

American burnweed is an increasingly common annual weed in wild blueberry fields in Atlantic Canada. Knowledge of susceptibility to several common herbicides used in wild blueberry, however, is lacking, and it is unclear how burnweed responds to clipping. Using greenhouse-grown plants, the objectives of this research were to evaluate burnweed susceptibility to various herbicides registered in wild blueberry and to determine the effect of clipping on burnweed lateral branch and flower production. Postemergence broadcast applications of mesotrione, flumioxazin, glufosinate, clopyralid, foramsulfuron, glyphosate, tribenuron methyl, nicosulfuron/rimsulfuron, terbacil, and hexazinone provided >90% control of burnweed. Postemergence spot applications of clopyralid, glyphosate, mesotrione, and nicosulfuron/rimsulfuron to 24 ± 0.3 cm tall burnweed plants caused 60%–97% injury, but <50% of treated plants died. In contrast, spot applications of glufosinate, tribenuron methyl, and foramsulfuron provided complete control of treated plants. Efficacy of postemergence broadcast mesotrione and foramsulfuron applications declined with increasing burnweed plant height, although foramsulfuron provided greater control of plants >10 cm in height than mesotrione. A tank mixture of mesotrione and foramsulfuron was effective on burnweed and may be useful for controlling plants of varying size with broadcast applications in the field. Removal of 25%, 50%, and 75% of aboveground burnweed stems with clipping increased lateral branch numbers relative to untreated control plants, and 100% removal of the aboveground stem was required to prevent lateral branching and flowering. Stem removal through mowing under field conditions will likely have limited effects on burnweed, and herbicides are recommended for burnweed management in wild blueberry.