Herbicide Formulations Research Articles

Environmental usefulness of PLA/PEG blends for controlled‐release systems of soil‐applied herbicides

ABSTRACTBlends consisting of biodegradable polylactide (PLA) and poly(ethylene glycol) (PEG) were investigated for their usefulness as an environmentally friendly herbicide formulation with prolonged activity. The aim of this study was to evaluate the release rate of selected soil‐applied herbicides from the PLA/PEG blend containing PEG of various molecular weights and to assess the phytotoxicity of the PEGs according to OECD 208 guidelines. The release rate of immobilized herbicides was correlated with degradation of the blends used. The progress of PLA/PEG blend degradation in water, soil, and activated sludge was estimated by sample weight loss, changes in blend composition, and microscopic observations of the blend surfaces during the experiment. The proposed formulation of the immobilized herbicide in a blend consisting of slowly biodegradable PLA and water‐soluble PEG provides the possibility to release the herbicides for a relatively long time, for approximately six months, which is a demand of weed management. The effect of PEGs on plant growth and development was dependent on both their concentration and molecular weight. With a higher concentration in soil and a higher molecular weight of PEG, a more harmful effect on plants was noticed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47856.

Carboxymethylcellulose-coated magnesium-layered hydroxide nanocomposite for controlled release of 3-(4-methoxyphenyl)propionic acid

Carboxymethylcellulose (CMC) acts as a coating material for a magnesium-layered hydroxide-3-(4-methoxyphenyl)propionate (MLH-MPP) nanocomposite via spontaneous self-assembly. The resulting product is called a magnesium-layered hydroxide-3-(4-methoxyphenyl)propionate/carboxymethylcellulose (MLH-MPP/CMC) nanocomposite. The XRD pattern of the MLH-MPP/CMC nanocomposite showed that MPP was maintained in the interlayers of the MLH, thus confirming that CMC is only deposited on the surface of the MLH-MPP nanocomposite. These findings were also supported by FTIR spectra, SEM and TEM. TGA data showed that the thermal stability of the intercalated MPP was significantly enhanced compared to pure MPP and uncoated nanocomposite. The release of MPP from the interlayers of MLH-MPP/CMC nanocomposite showed slower release than did uncoated nanocomposite and followed pseudo–second-order kinetics. Since the herbicide, MPP was released from the synthesised nanocomposite in a sustained manner, thus, it has excellent potential to be used as a controlled-release herbicide formulation.

Fate and effects of two pesticide formulations in the invertebrate Folsomia candida using a natural agricultural soil

Degradation rates of two widely used pesticides were assessed, and acute and chronic effects on a standard invertebrate species investigated. An herbicide (Montana®) and fungicide (Bravo500®) formulations were investigated and results were compared to the isolated active substances of each formulation (glyphosate and chlorothalonil, respectively). Tests were performed using the invertebrate Folsomia candida as test species and an agricultural natural soil. Degradation rate tests were determined under aerobic conditions at 20 ± 2 °C, using an ecologically relevant concentration of 5 mg (a.i.) kg−1 of soil for both chemicals. Results demonstrated degradation half-lives (DT50) of 2.2 days for Montana® and 2.8 days when pure glyphosate was tested. Values of 1.1 and 2.9 days were registered for Bravo500® and its active substance chlorothalonil, respectively. There were no effects on survival for the tested concentrations of both forms of the herbicide (up to 17.3 mg kg−1). However, reproduction was affected, but only by the herbicide formulation, with an estimated EC50 value of 4.63 mg (a.i.) kg−1. Effects were most unlikely related to glyphosate. For chlorothalonil, both tested forms affected survival and reproduction. The estimated LC50 values were 117 mg (a.i.) kg−1 and 73.5 mg (a.i.) kg−1, and the EC50 41.3 mg (a.i.) kg−1 and 14.9 mg kg−1 for the formulation and the active ingredient, respectively. The effects of the active ingredient were significantly stronger, indicating the major influence of the active substance in the effects caused also by the formulation. Overall results demonstrate the importance of evaluating the effects of the formulated chemicals, as they are applied in the field, and not only their isolated active ingredients.

Controlled Release of Herbicides Using Nano-Formulation: A Review

The intensive use of herbicides and other classes of chemicals products, in agricultural practices has resulted in serious environmental impact causing increasing level of herbicide residues in natural water, soil, and foodstuffs. Controlled release nano-formulation of herbicides in which the herbicides are incorporated in a nanosized matrix or carrier before application will be an excellent alternative over the conventional methods of herbicides application usually employed to control pathogens, weeds and several pests, thereby limiting the amount of the active ingredient available for unwanted processes. This review presents a better approach using nanotechnology for controlled release formulation of herbicides in agriculture.

A Mechanistic View of Interactions of a Nanoherbicide with Target Organism

Atrazine is one of the most used herbicides and has been associated with persistent surface and groundwater contamination, and novel formulations derived from nanotechnology can be a potential solution. We used poly(ε-caprolactone) nanoencapsulation of atrazine (NC+ATZ) to develop a highly effective herbicidal formulation. Detailed structural study of interaction between the formulation and Brassica juncea plants was carried out with evaluation of the foliar uptake of nanoatrazine and structural alterations induced in the leaves. Following postemergent treatment, NC+ATZ adhered to the leaf and penetrated mesophyll tissue mainly through the hydathode regions. NC+ATZ was transported directly through the vascular tissue of the leaves and into the cells where it degraded the chloroplasts resulting in herbicidal activity. Nanocarrier systems, such as the one used in this study, have great potential for agricultural applications in terms of maintenance of herbicidal activity at low concentrations and a substantial increase in the herbicidal efficacy.

Using fluazifop‐p‐butyl for low cost increases in lipid accumulation for the generation of algal biofuels from Chlorella vulgaris

The demand for sustainable, low‐emission fuels is increasing with the global expansion of industrialization. Biofuels have the potential to meet this need without the problematic addition of carbon into the earth's atmosphere. Algae, a potential biofuels feedstock, have the capability to quickly accumulate biomass under various conditions, including low‐nutritional growth medium and a reduced need for arable land. Current research is seeking to increase organismal efficiency in order to increase economic feasibility. Previous work has shown that exposing algae to environmental stressors or limitations, such as nitrogen deprivation, can increase lipid production in the cultures, though this is typically accompanied by a decrease in overall biomass. Nitrogen deprivation is also expensive to facilitate, so finding more economical methods is paramount to increasing algal biofuel feasibility. In this study, Chlorella vulgaris, a unicellular green alga, was exposed to a formulation of an inexpensive and readily available mass‐produced herbicide that targets acetyl Co‐A carboxylase with its active ingredient, fluazifop‐p‐butyl. The compositional changes of the algae cultures were monitored as well as the photosynthetic efficiency. Preliminary results have shown an increase in percent lipids in cultures exposed to the herbicide formulation, though the overall biomass decreased. Current results in this study will be presented.Support or Funding InformationThis research was made possible by NASA West Virginia Space Grant Consortium, Training Grant # NNX15AI01HThis material is based upon work supported by the National Science Foundation under Cooperative Agreement No. OIA‐1458952This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of Glyphosate Herbicide on Some Hematological and Biochemical Parameters in Carassius auratus L.

In recent years, commercial glyphosate herbicide formulations have been widely used in agriculture to control aquatic and terrestrial weeds. These pesticides may result in disruption of ecological balance, causing damage to nontarget organisms, including fish. Carassius auratus L. specimenes were exposed to glyphosate herbicide in concentration of 2.5mg/L and, respectively, 5 mg/L for 120 h, in laboratory condition. Thus, the effects of this chemical agent on both hematological parameters (hemoglobin, hematocrit, number of red blood cells) and on oxidative status indices (SOD, CAT, GPX, MDA) at Prussian carp experimental lots were analyzed. Our results showed, in comparison with the reference batch, the influence of glyphosate on the analyzed hematological and biochemical parameters, in close correlation with the administered pesticide dose.

Comparative studies on endogenic stress hormones, antioxidant, biochemical and hematological status of metabolic disturbance in albino rat exposed to roundup herbicide and its active ingredient glyphosate.

There have been growing concerns and uncertainty about reports attributing the metabolic disturbance induced by a commercial formulation of glyphosate-based herbicide to its active ingredient. We therefore compared the effects of Roundup Original® and its active ingredient glyphosate on some hypothalamic-pituitary-adrenal (HPA) hormones and oxidative stress markers, biochemical and hematological profiles in 56 adult male albino rats randomly assigned to seven treatments of eight rats per treatment. The rats were orally exposed to Roundup Original® and its active ingredient daily at 3.6mg/kg body weight (bw), 50.4 and 248.4mg/kgbw of glyphosate equivalent concentrations for 12weeks, while control treatment received distilled water. Serum concentrations of corticosterone, adrenocorticotropic hormone, aldosterone and concentration of oxidative stress marker, biochemical and hematological profiles in the blood were determined. Concentrations of corticosterone and aldosterone were significantly higher (p < 0.05) in rats treated with Roundup in a dose-dependent manner. Reduced glutathione concentration, catalase, and butyrylcholinesterase activities reduced significantly in rats treated with Roundup relative to those treated with the active ingredient. Lipid peroxidation was observed in rats treated with Roundup. Biochemical and hematological profiles of rats treated with Roundup were significantly altered (p < 0.05). However, significant changes in only acid phosphatase, lactase dehydrogenase, bilirubin, and white blood cells in rats treated with the active ingredient at 50.4mg/kg were observed. The severe metabolic disturbance and stress observed in rats treated with the commercial formulation of Roundup herbicide may not be associated with the mild changes induced by the active ingredient.

Synergistic effects of glyphosate formulation herbicide and tank-mixing adjuvants on Pardosa spiders

Glyphosate-based herbicides are the world’s most consumed agrochemicals, and they are commonly used in various agroecosystems, including forests, as well as in urban zones and gardens. These herbicides are sold as formulations containing adjuvants. Other tank-mixing adjuvants (most often surfactants) are commonly added to these formulations prior to application. According to the manufacturers of agrochemicals, such tank mixes (as these are known in agronomic and horticultural practice) have modified properties and perform better than do the herbicides as used alone. The effects of these tank mixes on the environment and on beneficial arthropods are almost unknown. Therefore, we studied whether a herbicide formulation mixed with adjuvant has modified effects on one of the most common genera of ground-dwelling wolf spiders vis-à-vis the herbicide formulation and adjuvants themselves. Specifically, we studied the synergistic effect in the laboratory on the predatory activity (represented by the number of killed flies) of wolf spiders in the genus Pardosa after direct treatment using the glyphosate-based herbicide formulation Roundup klasik Pro®, Roundup klasik Pro® in a mixture with the surfactant Wetcit®, Roundup klasik Pro® in a mixture with the surfactant Agrovital®, and the surfactants alone. We found that pure surfactants as well as herbicide-and-surfactants tank mixes significantly decrease the predatory activity of Pardosa spiders in the short term even as Roundup klasik Pro® did not itself have any such effect. Our results support the hypothesis that plant protection tank mixes may have modified effect on beneficial arthropods as compared to herbicide formulations alone. Therefore, testing of pesticide tank mixes is highly important, because it is these tank mixes that are actually applied to the environment.

DNA damage exerted by mixtures of commercial formulations of glyphosate and imazethapyr herbicides in Rhinella arenarum (Anura, Bufonidae) tadpoles.

Glyphosate (GLY) and imazethapyr (IMZT) are two herbicides commonly used worldwide, either alone or in mixtures. They represent key pesticides in modern agricultural management. The toxicity that results when employed as mixtures has not been characterized so far. Acute toxicity of the 48% GLY-based herbicide (GBH) Credit® and the 10.59% IMZT-based herbicide (IBH) Pivot® H alone and their binary combinations was analyzed in Rhinella arenarum tadpoles exposed in a semi-static renewal test. Lethal effects were determined using mortality as the end-point, whereas sublethal effects were determined employing the single-cell gel electrophoresis (SCGE) bioassay. Based on mortality experiments, results revealed LC5096 h values of 78.18 mg/L GBH and 0.99 mg/L IBH for Credit® and Pivot® H, respectively. An increase in the genetic damage index (GDI) was found after exposure to Credit® or Pivot® H at 5 and 10% of LC5096 h values. The combinations of 5% Credit®-5% Pivot® H LC5096 h and 10% Credit®-10% Pivot® H LC5096 h concentrations significantly enhanced the GDI in comparison with tadpoles exposed only to Credit® or Pivot® H. Thus, the effect of interaction between GBH and IBH inducing DNA damage in R. arenarum blood cells can be considered to be synergistic.

All Solid-State Poly (Vinyl Chloride) Membrane Potentiometric Sensor Integrated with Nano-Beads Imprinted Polymers for Sensitive and Rapid Detection of Bispyribac Herbicide as Organic Pollutant.

All-solid-state potentiometric sensors were prepared by using polyaniline (PANI) as the solid contact material. A film of PANI (thickness approximately being 0.25 µm) was deposited on a solid substrate (carbon screen printed platform). The PANI layer was subsequently coated with an ion-selective membrane (ISM) containing uniform-sized molecularly imprinted nanoparticles to produce a solid-contact ion-selective electrode (SC/ISE) for bispyribac herbicide (sensor I). In addition, aliquat 336 was also used as an ion exchanger in plasticized PVC membrane (sensor II). The proposed sensors revealed a remarkably improved sensitivity towards bispyribac ions with anionic slopes of −47.8 ± 1.1 (r2 = 0.9995) and −44.4 ± 1.4 (r2 = 0.9997) mV/decade over a linear range 1.0 × 10−2–8.6 × 10−6 M, 1.0 × 10−2–9.0 × 10−6 M and detection limits of 1.33 and 1.81 µg/mL for sensors I and II, respectively.Selectivity of both sensors is significantly high for different common pesticides and inorganic anions. The potential stability of the SC/ISEs was studied using chronopotentiometry. Electrochemical impedance spectrometry was used to understand the charge-transfer mechanisms of the different types of ion-selective electrodes studied. The impedance response of the electrodes was modelled by using equivalent electrical circuits. The sensors were used for a direct measurement of the bispyribac content in commercial herbicide formulations and soil samples collected from agricultural lands planted with rice and sprayed with bispyribac herbicide. The results agree fairly well with data obtained using HPLC method.

Mulch Type and Depth, Herbicide Formulation, and Postapplication Irrigation Volume Influence on Control of Common Landscape Weed Species

Mulch is often applied in landscape planting beds for weed control, but little research has focused specifically on mulch and preemergence (PRE) herbicide combinations. The objectives of this research were to determine the efficacy of herbicide + mulch combinations and which factors significantly affected weed control, including herbicide formulation and posttreatment irrigation volumes. Additional objectives were to determine efficacy derived from mulch or herbicides used alone under herbicide + mulch combinations and to identify differences in the additive (herbicide + mulch combinations) or singular (herbicide or mulch) effects compared with the use of herbicides or mulch only. Large crabgrass (Digitaria sanguinalis), garden spurge (Euphorbia hirta), and eclipta (Eclipta prostrata) were used as bioassay species for prodiamine, dimethenamid-P + pendimethalin, and indaziflam efficacy, respectively. The experiment consisted of a factorial treatment arrangement of two herbicide formulations (granular or spray applied), three mulch types [hardwood chips (HWs), pine bark (PB), and pine straw (PS)], two mulch depths (1 and 2 inches), and three levels of one-time, posttreatment irrigation volumes (0.5, 1, and 2 inches). Three sets of controls were used: the first set included three mulch types applied at two depths receiving only 0.5-inch irrigation volume, the second set included only two herbicide formulations and three one-time irrigation volumes, whereas the last set received no treatment (no herbicide or mulch) and only 0.5-inch irrigation volume. High levels of large crabgrass and garden spurge control (88% to 100%) were observed with all herbicide + mulch combinations evaluated at mulch depths of 1 inch or greater. When comparing mulch types, the best eclipta control was achieved with hardwood at 2 inches depth. The spray formulation of indaziflam outperformed the granular formulation in most cases when used alone or in combination with mulch. Overall, the results showed that spray formulations of prodiamine and dimethenamid-P + pendimethalin were more effective than granular formulations when applied alone, whereas indaziflam was more effective as a spray formulation when used both alone and in combination with mulch. Increasing irrigation volume was not a significant factor for any of the herbicide + mulch combinations when evaluating overall weed control.

The effects of glyphosate-based herbicide formulations on Lemna minor, a non-target species

Research into plants plays an important role in evaluations of water pollution with pesticides. Lemna minor (common duckweed) is widely used as an indicator organism in environmental risk assessments. The aim of this study was to determine by biological Lemna test and chemical methods the effect of glyphosate (GlyPh) concentrations of 0–40 μM on duckweed, an important link in the food chain. There are no published data on glyphosate's effects on the activity of enzymes of the amine biosynthesis pathway: ornithine decarboxylase, S-adenosylmethionine decarboxylase, tyrosine decarboxylase, lysine decarboxylase and arginine decarboxylase, and the content of shikimic acid and glyphosate residues in the tissues of common duckweed.It was found that glyphosate was taken up by duckweed. In plants exposed to 3 μM of glyphosate for 7 days, glyphosate content exceeded the acceptable Maximum Residue Level (MRL) 10-fold. Glyphosate accumulation in plant tissues exerted toxic effects on duckweed by decreasing its growth and yield, inhibiting the synthesis of chlorophyll a and b and carotenoids, and decreasing the photochemical activity of photosystem II (PSII). However, glyphosate increased the concentration of shikimic acid in the tested plants. The activity of ornithine decarboxylase increased 4-fold in plants exposed to 20 μM of the herbicide. As a water pollutant, glyphosate increased the content of biogenic amines tyramine, putrescine, cadaverine, spermidine and spermine. The activity of peroxidase and catalase was highest in duckweed exposed to 20 μM and 7 μM of the herbicide, respectively. The predicted toxic units were calculated based on glyphosate content and the computed EC values. The mean effective concentration calculated for all morphological and biochemical parameters of duckweed was determined at EC10 = 1.55, EC25 = 3.36, EC50 = 6.62 and EC90 = 14.08 μM of glyphosate. The study demonstrated that glyphosate, the active ingredient of Roundup Ultra 360 SL herbicide, induces morphological and biochemical changes in non-target plants and exerts toxic effects on aquatic ecosystems even during short-term exposure.

2,4-Dichlorophenoxyacetic acid containing herbicide impairs essential visually guided behaviors of larval fish

Aquatic herbicides are used worldwide to eradicate nuisance and invasive plants despite limited knowledge of their toxicity to non-target organisms. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a common active ingredient in commercial herbicide formulations, which triggers plant cell death by mimicking the plant-specific hormone auxin. Application practices of 2,4-D commercial herbicides typically coincide with yearly freshwater fish spawning periods. This practice exposes fish to xenobiotics at their vulnerable larval stages. The full impacts of 2,4-D on larval fish remains poorly understood, and hence, whether it may alter larval survival, larval behavior, fish populations, and ecosystem dynamics. In the present study, we exposed embryonic and larval zebrafish (Danio rerio) to the active ingredient 2,4-D (pure 2,4-D) or a 2,4-D containing commercial herbicide DMA4®IVM (DMA4) and evaluated morphology, survival, behavior, and nervous system function. At 2,4-D concentrations producing no overt morphological defects during embryonic or early larval stages, we observed reduced survival throughout a 21-day larval assay (4–8 ppm DMA4 and 0.75–4 ppm pure 2,4-D). Notably, prey capture, a behavior essential to survival, was reduced in 2,4-D-exposed larval zebrafish (4–8 ppm DMA4 and 0.75–4 ppm pure 2,4-D) and yellow perch (Perca flavescens) (4–20 ppm DMA4). In zebrafish, 8 ppm DMA4 exposure reduced prey capture when exposure was restricted to the period of visual system development. Consistent with these results, larval zebrafish exposed to 8 ppm DMA4 showed reduced neural activity within the optic tectum following prey exposure. Together, our results suggest that 2,4-D alters the development and function of neural circuits underlying vision of larval fish, and thereby reduces visually guided behaviors required for survival.

Degradation Dynamics of Halosulfuron-methyl in Two Textured Soils.

A laboratory experiment was conducted to study the degradation dynamics of halosulfuron-methyl residues in sandy loam and clay loam soil. The herbicide formulation was applied at 0.034 and 0.068mgkg- 1 equivalent to field application dose of 67.5 and 135ga.i.ha- 1 as single and double dose respectively. Soil samples were collected on 0 (1h), 1, 3, 7, 10, 15, 30 and 45days after treatments. Extraction was done using modified QuEChERS method. Residues were estimated by UPLC coupled with quadrupole Dalton mass detector. Average recoveries ranged from 85.5% to 94.5% for both soils at different fortification levels of 0.005 to 0.1mgkg- 1 with limit of detection (LOD) and limit of quantification (LOQ) as 0.001 and 0.005mgkg- 1, respectively. Dissipation followed first order kinetics with half-life of 8.4 to 10.7days in both soil at two doses. The residues reached below LOQ of 0.005mgkg- 1 after 45days of herbicide application.

Optimization and Characterization of Palm Oil-based Nanoemulsion Loaded with Parthenium hysterophorus Crude Extract for Natural Herbicide Formulation.

The present study revealed the optimization of nanoemulsion containing palm oil derivatives and Parthenium hysterophorus L. crude extract (PHCE) as pre-emergence herbicide formulation against Diodia ocimifolia. The nanoemulsion formulation was prepared by high energy emulsification method, and it was optimized by mixture experimental design (MED). From the optimization process, analysis of variance (ANOVA) showed a fit quadratic polynomial model with an optimal formulation composition containing 30.91% of palm kernel oil ester (PKOE), 28.48% of mixed surfactants (Tensiofix and Tween 80, 8:2), 28.32% of water and 12.29% of PHCE. The reading of both experimental and predicted particle size in the verification experiment were acceptable with a residual standard error (RSE) was less than 2%. Under the optimal condition, the smallest particle size obtained was 140.10 nm, and the particle was shown by morphology analysis to be spherical and demonstrated good stability (no phase separation) under centrifugation and different storage conditions (25 ± 5°C and 45°C). Nanoemulsion stored for 60 days exhibits monodisperse emulsion with a slight increase of particle size. The increase in particle size over time might have contributed by Ostwald ripening phenomenon which is shown by a linear graph from Ostwald ripening rate analysis. In the in vitro germination test, P. hysterophorus nanoemulsion (PHNE) was shown to cause total inhibition of D. ocimifolia seed at lower concentration (5 g L-1) as compared to PHCE (10 g L-1). The finding of the research could potentially serve as a platform for the development of palm oil based formulation containing plant crude extract for green weed management.

Effects of herbicide mixtures on freshwater microalgae with the potential effect of a safener

Freshwater microalgae are primary producers and cosmopolitan species subjected to the effects of herbicides. In this work, thein vitroalgal growth inhibitory effects of 11 agrochemicals (9 herbicides, 1 metabolite, and 1 safener) were quantified. Chemical compounds were applied singly and in specific mixtures. Three species were used in axenic condition: the green algaDesmodesmus subspicatus(Chodat), the diatomsNitzschia palea(Kützing) W. Smith andNavicula pelliculosa(Kützing) Hilse. When exposed to single compounds,N. paleaandN. pelliculosawere only sensitive to atrazine/desethylatrazine and the safener benoxacor (BE), respectively.D. subspicatuswas equally sensitive to four herbicides including atrazine and its metabolite and significantly more sensitive to iodosulfuron-methyl-sodium (IODO). The mixture of these five compounds induced a significantly higher growth inhibition of about 1.5-fold than IODO alone, which could be attributed to the four other herbicides. The mixture of all compounds was twofold less toxic than IODO onD. subspicatus. A halogen atom is present in IODO as in the herbicides to which the safener BE − known to induce glutathione-S-transferases − is associated in agrochemical preparations. We then showed that IODO was less toxic when combined with non-toxic concentrations of BE. These results indicated that the toxicity of the most active herbicide studied was decreased by a non-herbicide compound present in agrochemical formulations of other herbicides. These results suggest the importance to take into account the chemistry and the mechanisms of action for each compound in a risk assessment approach of a complex mixture.

Uticaj surfaktanata na efikasnost zajedničke primene kletodima i glifosata u suzbijanju Abutilon theophrasti Medik. i Chenopodium album L

Broadleaf weeds, Abutilon theophrasti Medik. and Chenopodium album L. are a major problem in glyphosate tolerant soybeans in the US. By applying compatible herbicides with different modes of action together, better efficiency is achieved, weed spectrum is expanded and the cost of weed control is reduced. This study was conducted with several goals: (1) to test the possibility of controlling weed species A. theophrasts and C. album with clethodim and glyphosate tankmixures, (2) to study the impact of surfactants on the efficacy of applied herbicides and (3) to determine whether synergistic and/or antagonistic interactions occur between clethodim and glyphosate in the control of velvetleaf and common lambsquarters. The study included 29 treatments. Treatments included glyphosate formulated without a surfactant (Touchdown HiTech), clethodim (SelectMak) formulated without a surfactant, glyphosate formulated with a surfactant (Roundup PoverMak) and formulations of both surfactant-free herbicides in a tank-mixures with the following surfactants: ATPlus DRT-EPS 0.25% vv-¹, ATPlus DRT 6000 0.25% vv-¹ and 0.5% vv-¹, Tveen 20 0.25% vv-¹, Tveen 22 0.5% vv-¹, Tveen L5-15 0, 5% vv-T, Tveen L10-10 0.5% vv-¹ and Tveen L15-5% vv-¹. The study was arranged as a completely randomized block design with four replications and two independent experimental runs. The effects of treatments on A. theophrasti showed that there were no significant interactions in most treatments. Treatments with clethodim and ATPlus DRT 6000 showed a synergistic effect, while treatments with clethodim and Tween L10-10 and clethodim and Tween L15-5 showed antagonistic effects on A. theophrasti. Two antagonistic reactions were observed in treatments where surfactants Tween 22 and Tween L5-15 were added to glyphosate formulated without a surfactant (Touchdown HiTech). None of the surfactants had an impact on the activity of clethodim in the case of C. album. However, when the surfactants were added to glyphosate, synergism occurred. That was confirmed in treatments with glyphosate formulated with surfactants. Synergistic interactions have also been confirmed when surfactants were added to the tank-mixures of glyphosate and clethodim, with the exception of ATPlus DRT-EPS.

Interactions among Glyphosate and Phosphate in Soils: Laboratory Retention and Transport Studies.

The purpose of this study was to determine the effect of PO on the sorption and transport of glyphosate [-(phosphonomethyl) glycine, GPS] in soils. The results of batch experiments indicated significant competition between PO and GPS in two different soils, with PO being preferentially sorbed. The 24-h Freundlich partitioning coefficients for GPS sorption were decreased by 50 to 60% with PO in solution. High sorptive capacities exhibited by soils in the presence of PO suggest the existence of both competitive and ion specific sites in either soil. Miscible displacement transport studies indicated limited effects of competition when GPS was applied in conjunction with or subsequent to pulses of PO. However, when a PO pulse was applied after the application of a GPS pulse, a secondary GPS breakthrough was observed where an additional 4% of the applied herbicide mass was recovered in the effluent solution. This is likely attributed to the PO-mediated displacement of GPS bound to competitive sites. These results are further emphasized by the distribution of residual herbicide in this column, with enrichment of mass at lower depths in the column and a corresponding decrease in GPS mass closer to the column surface. These results indicate that the timing of inorganic P fertilizers relative to GPS applications has a significant impact on the fate of the herbicide in soils. In particular, these findings suggest that GPS may be more liable to leaching in scenarios in which P fertilizers are applied after the application of GPS-based herbicidal formulations.

Behavior of pre-mix formulation of imazethapyr and imazamox herbicides in two different soils.

Imidazolinone group herbicides are known for longer persistence in soil. Therefore, a laboratory study was performed to evaluate the persistence of pre-mix formulation of two imidazolinone herbicides-imazethapyr and imazamox in clay and sandy loam soils. Herbicide formulation was applied at 70 and 140ga.i.ha-1 equivalent to recommended doses in legumes. For achieving efficient sample preparation, three methods namely ultrasonic-assisted extraction (UAE), matrix solid phase dispersion (MSPD), and solid phase extraction (SPE) were optimized. MSPD gave better recoveries (85.22 to 96.00%) over SPE (80.10 to 84.78%) and UAE (56.44 to 66.20%). Residues were estimated using gas chromatography tandem mass spectrometry (GC-MS/MS) which is previously not reported in open literature. Dissipation followed first-order kinetics and half-life period of 23.5 to 43.3days in clay loam and 19.6 to 39.8days in sandy loam soil. The results revealed the persistent nature of pre-mix formulation of both herbicides as only 64.2 to 86.6% residues dissipated after 90days of application in both soils.