Interaction Of Glyphosate Research Articles

Individual and combined effects of fine sediment and glyphosate herbicide on invertebrate drift and insect emergence: a stream mesocosm experiment

Pesticides and deposited fine sediment have been associated independently with changes in relative abundance and number of sensitive species in aquatic ecosystems, but the interplay between these stressors in agricultural streams is poorly understood. We used a 28-d experiment in outdoor streamside mesocosms to examine the effects of varying levels of fine sediment and a glyphosate-based herbicide on 2 important aspects of macroinvertebrate community dynamics, invertebrate drift and adult insect emergence. We applied 4 levels of each stressor in a full factorial, repeated-measures design (4 glyphosate × 4 sediment levels × 2 replicates of each treatment combination). We focused on the propensities of the invertebrates to drift or emerge (number drifting per mesocosm/benthic individuals per m2). Sediment addition affected drift propensities of 4 of the 10 most common invertebrate taxa, community-level measures of drift (total taxon and Ephemeroptera, Plecoptera, Trichoptera [EPT] richness) and adult emergence (total propensity and taxon richness), whereas glyphosate addition affected drift propensity of only 1 taxon. These results suggest that glyphosate entering streams during terrestrial herbicide operations may be less problematic for aquatic invertebrate community dynamics than fine sediment from catchment erosion. No significant sediment × glyphosate interaction was detected for any individual taxon drift propensity or community-level drift or emergence measure, indicating that the 2 stressors acted additively, rather than synergistically or antagonistically. The dynamic measures (invertebrate drift and adult insect emergence propensities) often showed the opposite pattern compared to benthic invertebrate densities in the same experiment, a result highlighting the value of using dynamic aspects of stream invertebrate communities to identify mechanisms underlying stressor effects on benthic standing stocks.

Interaction of Glyphosate with Zinc for the Yield, Photosynthesis, Soil Fertility and Nutritional Status of Soybean

ABSTRACTApplication of glyphosate herbicide in genetically modified (GM) soybean [Glycine max (L.) Merrill] in soils with low zinc (Zn) concentration may interfere in the uptake of this and other nutrients, with negative impact on productivity. Thus, an experiment was conducted in greenhouse conditions on Ustoxix Quatzipsamment soil to investigate the effects of the interaction of glyphosate with Zn for the yield, photosynthesis, soil fertility and nutritional status of soybean. The treatments consisted of two soybean varieties [BRS 133 (conventional—NGM) and its essentially derived transgenic line BRS 245RR (GM) with and without glyphosate application] and five Zn rates (0, 5, 10, 20 and 40 mg kg−1, source zinc sulfate (ZnSO4)), with four replicates. Except for the copper (Cu) and iron (Fe) concentrations, the introduction of the herbicide-resistant gene is the predominant factor reducing nutrient uptake, photosynthetic (A) rate, stomatal conductance (Gs), leaf chlorophyll and ureide concentrations. The administration of Zn rates lowered the leaf phosphorus (P) concentration, and there was significant increase in Zn concentration in the soil and in the plant. Except for the 20 mg kg−1 of Zn rate, the use of the herbicide did not affect the shoot dry weight (SDW) and seed yield, and on average, the maximum seed yield was obtained with Zn concentrations of 26.4 and 18.7 mg kg−1 extracted by Mehlich 1 and diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), respectively.

Mechanistic modeling of glyphosate interaction with rice husk derived engineered biochar

Biochar (BC), a carbon-rich solid product of biomass, and its surface activation via steam have been recognized as alternative economically viable strategy to decontaminate wastewaters. Existence of glyphosate, the most extensively used non-selective herbicide, in waters at elevated concentrations has received worldwide attention due to its ill consequences. The main objective of the present study was to investigate the potential of steam activated BC produced from rice husk (RHBC) via slow pyrolysis at 700 °C to remove glyphosate from aqueous solution. Batch adsorption experiments were carried out to evaluate the effects of pH, reaction time and glyphosate loading on the RHBC adsorption process. Results showed that a maximum removal of glyphosate (82.0%) occurred at pH 4, and the adsorption capacity decreased significantly with increasing pH. Both the Freundlich and Langmuir models fitted best to the equilibrium isotherm data suggesting physisorption as well as chemisorption mechanisms governing the glyphosate adsorption. The Langmuir maximum adsorption capacity was 123.03 mg/g. The kinetics of the adsorption process was well described by the pseudo-first order indicating that the glyphosate adsorption onto RHBC would be more inclined towards physisorption depending on the initial glyphosate concentration. Pore diffusion, π–π electron donor–acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption. Overall, steam activated RHBC could be a promising remedy of glyphosate removal from aqueous solution.

Effect of Glyphosate Application on Sudden Death Syndrome of Glyphosate-Resistant Soybean Under Field Conditions.

Sudden death syndrome (SDS), caused by Fusarium virguliforme, is an important yield limiting disease of soybean. Glyphosate is used to control weeds in soybean; however, its effect on SDS is not clearly understood. The objective of this study was to examine the impact of glyphosate on SDS, yield, and plant nutrition under field conditions. Fourteen field experiments were conducted in Iowa, Illinois, Indiana, Michigan, Wisconsin, and Ontario, Canada during 2011 to 2013. The experiment consisted of six treatment combinations of glyphosate and herbicides not containing glyphosate. Disease index was significantly different across the location-years, ranging from 0 to 65. The highest disease was noted in locations with irrigation, indicating that high soil moisture favors development of SDS. There were no effects of herbicide treatments or interactions on disease. The foliar disease index among the treatments over all years ranged from 9 to 13. Glyphosate-treatments also tended to yield more than treatments of herbicides not containing glyphosate. There were no interactions between glyphosate-treatments and total manganese in plant tissue. The interaction of glyphosate with other nutrients in plant tissue was inconclusive. This 14 location-year study demonstrated that glyphosate application did not increase SDS severity or adversely affect soybean yield under field conditions.

Interaction between glyphosate and mitochondrial succinate dehydrogenase

A recent study has evaluated the toxicity of the glyphosate-based herbicide, Roundup; the contents of the report evidences that the herbicide inhibits the mitochondrial succinate dehydrogenase activity. The present investigation, tries to prove the interaction of the active compound, glyphosate, with the succinate binding site of the enzyme, by using two-layer ONIOM calculations for structure optimization. In particular, the binding energy of the glyphosate-binding site complex model, in gas phase and polarized continuum medium in order to incorporate the protein environment, is calculated and compared it with a reference malonate-binding site complex model. The binding energy difference between these two model systems, ≈14kcalmol−1 at B3LYP/6-31+G(d) level of theory, supports the hypothesis of the interaction of glyphosate at the succinate binding site of the mitochondrial succinate dehydrogenase enzyme, verifying thus the experimental fact. Therefore, it is possible to conclude that glyphosate is harmful for the human health.

Understanding the combined influence of fine sediment and glyphosate herbicide on stream periphyton communities

Pesticides and deposited fine sediment have independently been associated with changes in relative abundance and species richness in aquatic ecosystems, but the interplay between these two stressors in agricultural streams is poorly understood. A 28-day experiment in outdoor stream mesocosms examined the effects of four levels each of fine sediment coverage (0, 25, 75, 100%) and glyphosate-based herbicide concentration (0, 50, 200, 370 μg/L) on periphyton communities (algae and bacteria) in a fully factorial, repeated-measures design. Our aims were to determine whether (i) increased levels of sediment and glyphosate had individual and/or additive effects, (ii) increased sediment reduced the toxicity of glyphosate (antagonistic multiple stressor interaction), or (iii) sediment-adsorbed glyphosate prolonged the effects of exposure (synergistic interaction). We also assigned all algal taxa to three ecological guilds (low-profile, high-profile and motile growth forms) and separately determined their responses to the treatments. As individual stressors, sediment addition affected all algal community-level metrics, whereas glyphosate addition only affected algal community evenness. Bacterial taxon richness was unaffected by either stressor. In combination, however, significant overall sediment by glyphosate interactions were detected, demonstrating synergistic (algal evenness, high-profile and motile guilds) or antagonistic effects (low-profile guild). Our experiment underscores the importance of considering both structural and functional indicators, including algal guild representation, when assessing the mechanisms by which periphyton communities respond to multiple stressors.

Suppression of glyphosate toxicity in plants following peroxide treatment

Food production is affected by rise in population, infertile soil, and water scarcity. Wheat and legumes are the major crops globally, but often encounter reduced growth due to various chemical and environmental stresses. The 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase is a key enzyme in the biosynthetic pathway of aromatic amino acid in plants and microbes. Glyphosate is a broad spectrum, non-selective herbicide, which acts as an inhibitor of EPSP. In contrast, reactive oxygen species (ROS) generated by hydrogen peroxide (H2O2) in soil is thought to provide growth stimulation in plants. It has been postulated that the oxidation of glyphosate may occur through ROS generated by H2O2 that acts as electron acceptor and may work via the modulation of EPSP and its degradation. Therefore, in this work in silico molecular docking studies were conducted showing blockade in the active cavity of EPSP by H2O2 that prevented the binding of glyphosate. The key amino acid residues of EPSP involved in the binding with glyphosate are His-385 and Lys-411, while H2O2 hinders the interaction of glyphosate with the aforesaid residues. The ERRAT plot provided 97.608 score and RAMPAGE displayed no outliers, which showed the validity of the modified 1G6S PDB structure of EPSP. In vivo studies further corroborated the inhibition of glyphosate by H2O2 and also growth promotion. This study provides a novel way to counteract glyphosate toxicity to commercially important crops.

Computer Simulation of the Interactions of Glyphosate with Metal Ions in Phloem

Essential nutrients such as trace metal ions, amino acids, and sugars are transported in the phloem from leaves to other parts of the plant. The major chelating agents in phloem include nicotianamine, histidine, cysteine, glutamic acid, and citrate. A computer model for the speciation of metal ions in phloem has been used to assess the degree to which the widely used herbicide glyphosate binds to Fe(3+), Fe(2+), Cu(2+), Zn(2+), Mn(2+), Ca(2+), and Mg(2+) in this fluid over the pH range of 8 to 6.5. The calculations show that glyphosate is largely unable to compete effectively with the biological chelating agents in phloem. At a typical phloem pH of 8, 1.5 mM glyphosate binds 8.4% of the total Fe(3+), 3.4% of the total Mn(2+), and 2.3% of the total Mg(2+) but has almost no effect on the speciation of Ca(2+), Cu(2+), Zn(2+), and Fe(2+). As the pH decreases to 6.5, there are some major shifts of the metal ions among the biological chelators, but only modest increases in glyphosate binding to 6% for Fe(2+) and 2% for Zn(2+). The calculations also indicate that over 90% of the glyphosate in phloem is not bound to any metal ion and that none of the metal-glyphosate complexes exceed their solubility limits.

Quantitative Evaluation of Noncovalent Interactions between Glyphosate and Dissolved Humic Substances by NMR Spectroscopy

Interactions of glyphosate (N-phosphonomethylglycine) herbicide (GLY) with soluble fulvic acids (FAs) and humic acids (HAs) at pH 5.2 and 7 were studied by (1)H and (31)P NMR spectroscopy. Increasing concentrations of soluble humic matter determined broadening and chemical shift drifts of proton and phosphorus GLY signals, thereby indicating the occurrence of weak interactions between GLY and humic superstructures. Binding was larger for FAs and pH 5.2 than for HAs and pH 7, thus suggesting formation of hydrogen bonds between GLY carboxyl and phosphonate groups and protonated oxygen functions in humic matter. Changes in relaxation and correlation times of (1)H and (31)P signals and saturation transfer difference NMR experiments confirmed the noncovalent nature of GLY-humic interactions. Diffusion-ordered NMR spectra allowed calculation of the glyphosate fraction bound to humic superstructures and association constants (K(a)) and Gibbs free energies of transfer for GLY-humic complex formation at both pH values. These values showed that noncovalent interactions occurred most effectively with FAs and at pH 5.2. Our findings indicated that glyphosate may spontaneously and significantly bind to soluble humic matter by noncovalent interactions at slightly acidic pH and, thus, potentially pollute natural water bodies by moving through soil profiles in complexes with dissolved humus.

Bases for Interactions between Saflufenacil and Glyphosate in Plants

Buckwheat (Fagropyrum esculentum Moench.), cabbage (Brassica oleracea L), and conventional and glyphosate-resistant varieties of canola (Brassica napus L.) were used to study the bases of saflufenacil and glyphosate interactions. Compared to the addition of Merge (surfactant), the addition of both Transorb (i.e., commercial product, Transorb formulation with glyphosate) and Merge increased the cuticular absorption of [(14)C] saflufenacil in cabbage plants with thick epicuticular wax layers. However, in all cases, the addition of glyphosate reduced the translocation of [(14)C]saflufenacil in glyphosate-susceptible plants, while translocation was not affected in glyphosate-resistant canola. Moreover, the phytotoxicity of saflufenacil reduced the activity of glyphosate, possibly by reducing its translocation in all plant species studied. Increased absorption of saflufenacil by the addition of Transorb (i.e., Transorb formulation with glyphosate) plus Merge appears to increase its contact activity, thus the interaction of saflufenacil and glyphosate involves two separate processes, absorption and translocation.

Interaction of Glyphosate and Pelargonic Acid in Ready-to-Use Weed Control Products

Glyphosate-based, ready-to-use weed control products often contain pelargonic acid (PA) at a concentration equivalent to that of the glyphosate. It remains unclear what benefit, if any, this combination provides. Greenhouse experiments using large crabgrass, yellow nutsedge, longstalked phyllanthus, and prostrate spurge were conducted to determine whether the addition of PA improved weed control efficacy compared to glyphosate alone. Glyphosate was applied at a series of rates, ranging from 0.11 to 1.12 kg ae/ha, either alone or with an equal rate of PA. Addition of PA to glyphosate was synergistic only in longstalked phyllanthus and yellow nutsedge, and this synergism was manifested only as an increase in the amount of early (i.e., 5 to 7 d after treatment) visual injury. Conversely, longer-term control and control of regrowth was either not affected or reduced by the addition of PA. We conclude that the addition of PA to glyphosate in ready-to-use weed control products is neither warranted nor justified. However, we also note that the increase in early injury that was observed in only two of the four species evaluated could be an important attribute for the consumers for which these products are targeted.

No‐Tillage Improves Broomrape Control with Glyphosate in Faba‐Bean

Broomrape (Orobanche crenata Forsk.) causes considerable losses in faba‐bean (Vicia faba L.) production in the Mediterranean region. The application of an ultra‐low glyphosate rate at an early broomrape parasitic phase, i.e., tubercle development, is the most common control system. This study sought to determine the effect of tillage system and glyphosate application on broomrape infestation, faba‐bean yield, and yield components. A field experiment was performed over a 3‐yr period in Cordoba (Spain) in a rainfed Vertisol. Experimental factors and respective treatments were: tillage system (no‐tillage vs. conventional tillage) and glyphosate application (none vs. 0.113 kg a.i. ha−1). Year × tillage system × glyphosate interactions were apparent in the results. Averaging over 3‐yr, no‐tillage with glyphosate application reduced weed infestation (42 plants m−2) and increased faba‐bean seed yield (1.73 Mg ha−1) in comparison with conventional tillage with glyphosate application (10 broomrape plants m−2, and 1.14 Mg ha−1 of seed yield). When glyphosate was not applied, broomrape density varied from 80 to 45 plants m−2 and faba‐bean seed yield from 0.50 to 1.24 Mg ha−1 for tillage and no‐tillage systems, respectively. Within each tillage system, glyphosate application always reduced broomrape infestation and increased seed yield. Even in the absence of glyphosate application, seed yields were higher under no‐tillage than under conventional tillage with herbicide application over 2 yr. Pod m−2 was the yield component most affected by broomrape infestation. No‐tillage is an important tool for broomrape control, but the addition of glyphosate application substantially enhances the degree of control.

Construction and Assessment of Reaction Models of Class I EPSP Synthase: Molecular Docking and Density Functional Theoretical Calculations

The high frequency of contamination by herbicides suggests the need for more active and selective herbicides. Glyphosate is the active component of one of the top-selling herbicides, which is also a potent EPSP synthase inhibitor. That is a key enzyme in the shikimic acid pathway, which is found only in plants and some microorganisms. Thus, EPSP synthase is regarded as a prime target for herbicides. In this line, molecular modeling studies using molecular dynamics simulations and DFT techniques were performed to understand the interaction of glyphosate and its analogs with the wild type enzyme and Gly96Ala mutant EPSP synthase. In addition, we investigated the reaction mechanism of the natural substrate. Our findings indicate some key points to the design of new selective glyphosate derivates.

Analysis of Wild-Type and Gly96Ala Mutant EPSP Synthase Structures via in Silico Docking with Inhibitors and Molecular Dynamics Simulation

The high frequency of contamination by herbicides suggests the need for more active and selective herbicides. Glyphosate is the active component of one of the top-selling herbicides, which is also a potent EPSP synthase inhibitor. That is a key enzyme in the shikimic acid pathway, which is found only in plants and some microorganisms. Thus, EPSP synthase is regarded as a prime target for herbicides. In this line, molecular modeling studies using molecular dynamics simulations and molecular docking techniques were performed to understand the interaction of glyphosate and its analogs with the wild type enzyme and Gly96Ala mutant EPSP synthase. Our findings indicate some key points for the designing new selective glyphosate derivates.

Weed Response to Foliar Coapplications of Glyphosate and Zinc Sulfate

Field trials were conducted during 2006 and 2007 and a container study was performed twice in 2007 at the Dean Lee Research and Extension Center in Alexandria, LA to evaluate the interaction of glyphosate and zinc coapplied to selected weeds. Across all experiments, no differences in either visible weed control or weed fresh weight were detected among glyphosate formulations. In the field studies, weed control was greatest when glyphosate was applied alone, in which case control of barnyardgrass, browntop millet, and Palmer amaranth ranged between 93 and 95%. When glyphosate was coapplied with formulations of zinc, control of the aforementioned weed species was reduced to 39, 39, and 45%, respectively. Visual estimates of weed control in the container studies showed glyphosate performance to be the highest (82 to 98%) in the absence of zinc for control of barnyardgrass, browntop millet, johnsongrass, ivyleaf morningglory, and redroot pigweed. Across all weed species, control was reduced 43 to 59% when zinc was coapplied with glyphosate. Similar results were noted in reduction of weed fresh weights. Results indicate that glyphosate-based weed control is reduced when coapplied with the zinc products at their current use rates. Producers should be aware of this antagonism and these coapplications should not be recommended.

Interaction of Glyphosate and Diquat in Ready-To-Use Weed Control Products

Glyphosate-based, ready-to-use weed control products frequently contain diquat (typically, 0.04 by weight relative to glyphosate) under the supposition that the diquat, “makes glyphosate work faster.” However, in light of the known modes of actions of glyphosate and diquat, we hypothesize that diquat may be antagonistic to glyphosate activity. Greenhouse experiments using longstalked phyllanthus were conducted to test this hypothesis. Glyphosate was applied at a series of rates, ranging from 0.11 to 1.12 kg ae/ha, either alone or tank-mixed with either 0, 0.02, 0.04, and 0.06 diquat. Onset of visual injury was more pronounced with the glyphosate + diquat tank mixtures compared with glyphosate alone. However, long-term control, as expressed by regrowth suppression, was greater with glyphosate alone. Regression analysis indicated that, at marginally effective glyphosate rates, the amount of glyphosate must be increased by approximately 60% to compensate for the diquat-based antagonism. Absorption and translocation studies using 14C-glyphosate revealed that the antagonism of diquat toward glyphosate can be attributed to reduced translocation of absorbed glyphosate.

Influence of Soil Moisture on Root Colonization of Glyphosate‐Treated Soybean by Fusarium Species

The widespread use of glyphosate‐resistant (GR) cropping systems may impact rhizosphere microbial associations and crop productivity. It was previously reported that glyphosate accumulation in the rhizosphere may stimulate colonization of soybean [Glycine max (L.) Merr.] roots by soilborne Fusarium. Field studies often reveal inconsistent root colonization by Fusarium, especially during growing seasons characterized by contrasting rainfall patterns. Therefore, this study was conducted to determine the impact of different soil moisture contents on root colonization of glyphosate‐treated soybean by Fusarium species. Glyphosate (0.84 kg ae ha−1) was applied to greenhouse‐grown glyphosate‐resistant (GR) soybean at the two to three trifoliate-leaf (V2–V3) growth stage growing in a Mexico silt loam at 27%, 13%, and 10% soil moisture contents. Soil and plant samples were sampled periodically after herbicide application and selectively cultured for Fusarium. Highest Fusarium colonization was associated with the glyphosate treatment, with maximum levels occurring at the highest soil moisture level. Thus, glyphosate interactions with root colonization by Fusarium in glyphosate‐resistant soybean are greatly influenced by soil moisture content.

Elevated Atmospheric Carbon Dioxide and Weed Populations in Glyphosate Treated Soybean

ABSTRACTAlthough rising atmospheric carbon dioxide (CO2) is known to stimulate the growth of agronomic weeds, the impact of increasing CO2 on herbicide efficacy has not been elucidated for field‐grown crops. Genetically modified soybean [Glycine max (L.) Merr.] (i.e., Round‐up Ready soybean) was grown over a 2‐yr period at ambient and projected levels of atmospheric carbon dioxide (CO2, 250 μmol mol−1 above ambient), with and without application of the herbicide, glyphosate [N‐(phosphonomethyl)glycine], to assess the impact of rising atmospheric carbon dioxide concentration [CO2] on chemical efficacy of weed control. For both years, soybean showed a significant vegetative response to elevated [CO2], but no consistent effect on seed yield. For 2003, weed populations for all treatments consisted entirely of C4 grasses, with no [CO2] effects on weed biomass (unsprayed plots) or glyphosate efficacy (sprayed plots). However, in 2004, weed populations were mixed and included C3 and C4 broadleaves as well as C4 grasses. In this same year, a significant increase in both C3 broadleaf populations and total weed biomass was observed as a function of [CO2] (unsprayed plots). In addition, a [CO2] by glyphosate interaction was observed with significant C3 broadleaf weed biomass remaining after glyphosate application. Overall, these data emphasize the potential consequences for CO2–induced changes in weed populations, biomass, and subsequent glyphosate efficacy in Round‐up Ready soybean.

Glyphosate interaction with manganese in tank mixtures and its effect on glyphosate absorption and translocation

Abstract Recent reports indicate that manganese (Mn), applied as a foliar fertilizer in tank mixtures with glyphosate, has the potential to antagonize glyphosate efficacy and reduce weed control. It was hypothesized that Mn2+ complexed with glyphosate in a similar manner to Ca2+, forming salts that were not readily absorbed and, thereby, reducing glyphosate efficacy. This study was conducted to confirm the interaction of Mn2+ and glyphosate and to measure the effect of Mn on glyphosate absorption and translocation in velvetleaf. In aqueous solutions, Mn2+ binds with solvent molecules and with chelating agents to form hexacoordinate complexes. The distribution of paramagnetic species, both the free manganous ion ([Mn{H2O}6]2+) and the Mn2+–glyphosate complex, in Mn–glyphosate solutions at various pH values were analyzed using electron paramagnetic resonance (EPR) spectroscopy. Glyphosate interaction with Mn appeared to increase as the pH was increased from spray solution levels (2.8 to 4.5) to levels commo...

Soybean (Glycine max) Response to Glyphosate and Soybean Cyst Nematode (Heterodera glycines)1

Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant ...