Release of atrazine and alachlor from clay-oxamide controlled-release formulations

Controlled-release herbicide formulations have been shown to decrease the leaching potential of several herbicides under laboratory and field conditions. The utility and efficacy of these formulations may be improved by combining several herbicides and a fertilizer source in a single formulation. The objective of these studies was to develop granular alginate formulations that were composed of a combination of the herbicides atrazine and alachlor with the slow-release nitrogen source oxamide (ethanediamide). Controlled release of the herbicides was obtained by addition of selected minerals, including calcium bentonite, fine-grind bentonite, montmorillonite K10, kaolinite and iron (III) oxide. A formulation without clay was used as a comparison. The formulations tested had herbicide active ingredient contents ranging from ∽0·02 to 0·54% and a nitrogen content of 21%. Release of the herbicides was studied by equilibrating the formulations with deionized water on a rotary shaker at 200 rev min^-1 and sampling at regular time intervals up to 104 hours. The minerals used in the different formulations influenced the herbicide active ingredient composition, as well as the release properties of the individual formulations. The atrazine content of the formulations decreased in the order calcium bentonite>fine-grind bentonite>kaolinite>montmorillonite=iron oxide>no clay. For alachlor the content decreased in the order of calcium bentonite>fine-grind bentonite>montmorillonite>iron oxide>kaolinite>no clay. Controlled release of atrazine (i.e. reduction in release rate) varied in the order calcium bentonite>iron oxide>montmorillonite>fine-grind bentonite= kaolinite>no clay, and for alachlor fine-grind bentonite>calcium bentonite>montmorillonite>no clay=kaolinite=iron oxide. A certain percentage of the applied active ingredient of both alachlor and atrazine was not recovered. From 5 to 27% of the active ingredient was not released, with the greatest retention by the bentonite formulations. Release of nitrogen was not strongly influenced by mineral type, although a trend indicated greater release with formulations containing kaolinite. © 1998 SCI     

Formulation affecting alachlor efficacy and persistence in sandy soils

BACKGROUND: The development of controlled‐release formulations of alachlor to extend the period of weed control was studied. This extended duration reduces the need for high herbicide application rates that could lead to environmental contamination. For this purpose, the influence of formulation, as well as the influence of soil characteristics, on alachlor efficacy and persistence in soil of a commercial formulation (CF) and different ethylcellulose microencapsulated formulations (MEFs) was evaluated. RESULTS: Higher alachlor rates yielded an enhanced initial herbicidal activity. The prolonged release of alachlor provided by the MEFs resulted in a higher herbicidal efficacy and a longer period of weed control compared with the effects of CF in the two soils tested (at 40 days after treatment, oat growth inhibition for CF and MEFs was 1.96% and 93.5% respectively). Soil characteristics strongly influenced alachlor efficacy and weed control by MEFs. The highest alachlor efficacy and persistence were observed in the soil with lowest microbial activity and clay and organic matter content. CONCLUSIONS: The use of MEFs can be advantageous because they permit the maintenance of the desired concentration of the herbicide in the soil for longer periods of weed control. Copyright © 2009 Society of Chemical Industry     

Controlled release of isoproturon from an alginate–bentonite formulation: water release kinetics and soil mobility

The herbicide isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethylurea] was incorporated in alginate‐based granules to obtain controlled‐release (CR) properties. The basic formulation (sodium alginate (1.87%)–isoproturon (0.67%) in water) was modified by addition of different sorbents. The effect on isoproturon release rate, modified by the incorporation of natural and acid‐treated bentonite in alginate formulation, was studied by immersion of the granules in water while shaking. The release of isoproturon was diffusion‐controlled. The time taken for 50% of the active ingredient to be released into water, T₅₀, was longer for those formulations containing added bentonite (5.98 and 7.43 days, for natural and acid‐treated (1 M H₂SO₄) bentonite, respectively) than for the preparation without bentonite (3.78 days). The mobilities of non‐formulated technical grade (98%) and formulated isoproturon were compared using soil columns. The use of alginate‐based CR formulations containing bentonite reduced isoproturon movement compared with the technical product. Sorption capacity of the soil for isoproturon was measured using batch experiments (0.29 litre kg⁻¹) and the results obtained here in agreement with those obtained under dynamic conditions. © 2000 Society of Chemical Industry     

Bioefficacy and leaching of controlled-release formulations of triazine herbicides

Conventional formulations of atrazine and simazine were compared with controlled-release formulations of these two herbicides for bioefficacy, leaching and crop safety in laboratory and field experiments. Three light-textured soils with a pH range of 5.8–8.5 were used for this work. An oat bioassay (Avena sativa L.) was used to quantify soil concentrations of the herbicides. Comparison of the initial bioefficacy of controlled-release formulations of atrazine and simazine showed their respective relative potencies to conventional formulations to be 0.51–0.85. The results indicated that the controlled-release formulations maintained an entrapped reserve of active ingredient after delivery with a conventional boomsprayer. In laboratory trials, the controlled-release formulations showed a reduction in leaching compared with conventional formulations. A controlled-release formulation and a conventional formulation of atrazine were tested further in a field trial. A higher concentration of atrazine in topsoil from the controlled-release formulation was observed 11 weeks after application after 107 mm of rainfall. It was deduced that this was caused by reduced leaching of the controlled-release formulation, as observed in laboratory trials. EWRC scores for the control of a range of grass and broad-leaved weeds were identical for both formulations. This indicated that, while the controlled-release formulation could inhibit leaching of the active ingredient, it did not hinder the level of potency necessary for early weed control. EWRC crop safety ratings of chickpeas (Cicer arietinum L.) sown at application were higher for the controlled-release formulation 10 weeks after sowing, and subsequent harvest yields were 50% higher. It was inferred that this resulted from a favourable interaction between crop growth and the timing of the release of the active ingredient from the controlled-release formulation. Altogether, the controlled-release formulations displayed the necessary prerequisites for their further development for large-scale use under arable regimes.     

Evaluation of the bioefficacy and leaching of a controlled–release formulation of chlorsulfuron

A controlled–release formulation of chlorsulfuron (DT26B) and a conventional granular formulation were compared for their initial bioefficacy and leaching in laboratory and field experiments. Three alkaline soil types, representative of farm soils in SE Australia, were used for these experiments. Laboratory tests of initial bioefficacy using a Mallee sand (pH 7.2) were able to detect, within ED_05–95 limits, that approximately 50% of active ingredient remained as a non–available reserve in DT26B immediately after spraying, when compared with the granular formation. There was also an indication that the bioavailable component of active ingredient in DT26B would be sufficient for weed control. This was confirmed at field sites on a Kattyoong sand (pH 7.9) and a Wimmera Grey clay (pH 8.4), after using recommended application rates of chlorsulfuron during the 1994 winter growing season. The formulations produced only marginal differences in control of Lolium rigidum Gaud. The field leaching trials at these sites showed that there can be rapid leaching of chlorsulfuron with only small amounts of rainfall. Under these conditions, there was an overall trend of reduced leaching by DT26B at both trial sites, although these reductions were not significant when compared with the granular formation, A laboratory system designed to measure the mobility of herbicides is described. It was used to impose upon each formulation a greater level of leaching than in the field trials, using Mallee sand columns irrigated with 50 mm day^–1 under –50 kPa suction. This test revealed a negligible reduction in leaching of chlorsulfuron by DT26B as compared with the granular formulation. Therefore, although the controlled–release formulation DT26B demonstrated that it could provide a viable alternative for weed control under conventional spraying conditions in arable farming, the agricultural usage of DT26B for the purpose of reducing leaching could not be warranted at its current stage of development.     

Green nanoemulsion‐laden glyphosate isopropylamine formulation in suppressing creeping foxglove (A. gangetica), slender button weed (D. ocimifolia) and buffalo grass (P. conjugatum)

BACKGROUND: Pesticides are developed with carriers to improve their physicochemical properties and, accordingly, the bioefficacy of the applied formulation. For foliar‐applied herbicide, generally less than 0.1% of the active ingredient reaching the target site could reduce pesticide performance. Recently, a carrier of nanoemulsion consisting of oil, surfactant and water, with a particle size of less than 200 nm, has been shown to enhance drug permeability for skin penetration in pharmaceutical delivery systems. In the present work, the aim was to formulate a water‐soluble herbicide, glyphosate isopropylamine (IPA), using a green nanoemulsion system for a biological activity study against the weeds creeping foxglove, slender button weed and buffalo grass. RESULTS: The nanoemulsion formulations displayed a significantly lower spray deposition on creeping foxglove (2.9–3.5 ng cm^?2), slender button weed (2.6–2.9 ng cm^?2) and buffalo grass (1.8–2.4 ng cm^?2) than Roundup^® (3.7–5.1 ng cm^?2). The visible injury rates of weeds treated with the nanoemulsion formulations were statistically equivalent to those relating to Roundup^® at 14 days after treatment, with a control range of 86.67–96.67%. CONCLUSION: It was hypothesised that the significant difference in spray deposition with equal injury rates can be attributed to enhanced bioactivity of the nanoemulsion formulations. This initial discovery could be the platform for developing better penetration of agrochemical formulations in the future. Copyright © 2012 Society of Chemical Industry     

Slow release pirimicarb granular formulations: Measurements of release rate under field conditions

Various granular formulations based on a non-disintegrating granular carrier of the aphicide, pirimicarb, were tested for release rate under natural conditions by placing the granules in small bags made of a non-woven fabric in various soils and analysing the contents at monthly periods. There was complete release from the control formulation within 1 month. The other formulations contained slow release additives. These slowed down the release rate but half of the active ingredient was still released in the first month from the formulation with the slowest release rate. It appears that if very slow rates of release are required than a different type of granule is needed. Laboratory release rates bear some relationship to field results justifying the use of laboratory tests as a method for selecting a short list of formulations for testing in the field.     

Movement of metolachlor in soil: effect of new organo-clay formulations

The use of commercially available formulations of metolachlor has resulted in its leaching and migration to water sources. Formulations of metolachlor designed to reduce its leaching in soil have been prepared by adding the herbicide dissolved in an organic solvent or in water to organo-clay complexes. Best formulations were made when the organo-clay complex was formed by adsorbing the monovalent organic cations benzyltrimethylammonium (BTMA) or benzyltriethylammonium (BTEA) onto sodium montmorillonite (Mont) at 0.5 or 0.8 mole kg⁻¹ clay. Adsorption of metolachlor to organo-clays followed the sequence Mont-BTMA 0.5 > Mont-BTMA 0.8 > Mont-BTEA 0.8 > Mont-BTEA 0.5 > Mont. Fourier transform infrared (FTIR) analysis demonstrated the occurrence of shifts of several peaks of adsorbed metolachlor relative to the free herbicide, indicating the existence of strong interactions between metolachlor molecules and the organo-clay surface. Leaching studies employing organo-clay and commercial formulations were carried out under greenhouse and field conditions. Metolachlor applied as organo-clay formulations leached less than the commercial formulation. Organo-clay formulations prepared by adding the herbicide as a water solution showed less leaching in the soil profile than those made by using organic solvent. Under greenhouse conditions, the herbicidal activity of organo-clay formulations was similar to that of the commercial one. Under field conditions, leaching from Mont-BTMA 0.5-metolachlor was less than that from the commercial formulation, demonstrating the environmental and agricultural advantages of the organo-clay formulations of metolachlor. © 1999 Society of Chemical Industry     

Retention and degradation of metribuzin in sandy loam and clay soils of Lebanon

The retention and degradation of metribuzin herbicide were studied under two environmental conditions. Field studies were carried out on two soils, a sandy loam soil (soil A) and a clay soil (soil B). Metribuzin was applied with a jet sprayer at 1060 g a.i. ha^?1 and 1960 g a.i. ha^?1 on soils A and B respectively. Reconstituted soil columns were used to study the herbicide movement and metabolism in the two soils. Analyses of metribuzin and its metabolites were carried out using standardized methods. The results indicated a very weak capacity of adsorption of metribuzin in the two soils, and the weak adsorbed fraction is easily desorbed. Degradation and mobility of metribuzin in the field and laboratory soil columns were very intense and rapid. Soil A favoured reductive deamination whereas soil B favoured oxidative desulphuration and the respective metabolites deaminometribuzin and diketometribuzin yield the same product deaminodiketometribuzin. Both leaching by rainfall and degradation were important in the disappearance of metribuzin from the soils.     

复合改性粘土对除草剂2,4-D的控制释放作用研究

采用无机/有机复合改性粘土作制剂载体,探讨了其对阴离子型除草剂2,4-D的控制释放作用,目的在于延长2,4-D的持效期,同时减轻其污染。利用无机和有机改性的结合优势,复合改性粘土具有更强的吸附性能,能够显著延缓2,4-D在水中和土壤中的释放。分析其水中释放动力学数据得出,2,4-D释放50%所需时间(t50)长达73.8 h,远大于有机改性粘土作载体时的1 h。土壤层释放实验表明,当2,4-D载药量在20~80 mg/g之间时,复合改性粘土均能保持良好的控制释放效果。     

Herbicide Effects on Sugarcane Growth, Pythium Root Rot, and Pythium arrhenomanes

ABSTRACT Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.     

Preparation of controlled-release formulations of 14C-labelled thiobencarb herbicide and study of their environmental behaviour

Controlled-release formulations of ¹⁴C-labelled thiobencarb herbicide were prepared in calcium alginate using kaolin as an inexpensive filler. The rates of release of the herbicide from these and from a commercial granular formulation were studied in static distilled water contained in open and closed vessels. The rate of release of the herbicide was much higher from the commercial formulation than from the controlled-release formulations. Increasing the proportion of kaolin to calcium alginate in controlled-release formulations reduced the rate of release of the herbicide. There was a significant loss of thiobencarb-related radioactivity from the water solution when the vessels containing the solutions were left uncovered and exposed to light. The loss of the herbicide seemed to be due to degradation and evaporation.     

Prognose-Modell zur Erfassung des Rückstandsverhaltens von Metribuzin und Methabenzthiazuron im Boden und deren Auswirkungen auf Folgekulturen

A predictive model for the assessment of metribuzin and methabenzthiazuron residues in soil and their effects on succeeding crops Aus der simulierten Abbaukurve lassen sich somit für jeden beliebigen Zeitraum nach Applikation eines Herbizids die maximalen pflanzenverfügbaren Wirkstoffanteile ableiten, aus denen die Auswirkungen auf mögliche Folgekulturen prognostiziert wurden. Die relative Empfindlichkeit (im Bereich der ED₅₀) der untersuchten Kulturpflanzen in Hydroponik war bei Metribuzin: Möhre < Bohne = Salat < Erbse = Spinat und bei MBT: Bohne = Erbse = Salat < Spinat = Möhre. Weiterhin konnte gezeigt werden, dass unter Labor- und Freilandbedingungen evtl. auftretende Schäden in fast allen Fällen in den gleichen Aktivitäskategorien lagen. The degradation of the herbicides metribuzin and methabenzthiazuron (MBT) was simulated under outdoor conditions in a sandy soil by a computer model based on the dominating influence of temperature and moisture on degradation, which is measured in preceding laboratory experiments. Depending on the conditions of incubation (10–30°C, 20–90% water holding capacity) the half-life of metribuzin was 11–60 days and of MBT 42 > 1200 days. Knowing the plant available soil water, the fraction of a total herbicide residue potentially available to plants can be calculated from the distribution coefficient (K_d-value). In the soil under investigation, for metribuzin 77% and for MBT 16% of the total residue was available to plants. Thus, the maximum residue available to plants can be calculated from the simulated degradation curve for any period after the application of a herbicide and in combination with a predictive model the effect on succeeding crops can be predicted. The specific susceptibility of the crops in question has to be established in preceding hydroponic culture experiments. The relative susceptibility (about ED₅₀) of the plants in hydroponic-culture was earrot相似文献   

The influence of soil properties on the rates of degradation of metamitron,metazachlor and metribuzin

The rates of degradation of metamitron, metazachlor and metribuzin were measured in 12 mineral soils and the first order rate constants were compared with soil properties by regression analysis. Rates of metamitron degradation were best described by a multiple regression involving the silt content of the soil and the fraction of the total herbicide content which was available in the soil solution. Metazachlor degradation was best described by a multiple regression involving the sand content of the soil, the availability of the herbicide in the soil solution and soil microbial respiration. There was evidence that metribuzin degradation in any one soil was closely related to microbial activity, and rate constants per unit microbial respiration were derived for each soil. These rate constants were best described by a multiple regression involving the Freundlich adsorption constant and the sand content of the soils. The best regression equations for each herbicide were tested against observed degradation rates in an additional group of six soils. The calculated rates compared favourably with those observed for both metamitron and metazachlor, but with metribuzin, there was good agreement with one soil only.     

Effects of tillage, application time and rate on metribuzin dissipation

Metribuzin efficacy and dissipation were determined in two silty clay loam soils following preplant (PP), pre-emergence (PRE) and split (PP+PRE) application to tilled and no-till soybeans in rotation with corn at Clay Center and Lincoln, Nebraska. A similar experiment was conducted in tilled and no-till soybeans in rotation with wheat at Lincoln. Corn and wheat residue in no-till plots reduced the amount of metribuzin that reached the soil by approximately 54 and 89%, respectively. No differences in weed control or soybean yield were observed between tillage treatments or time of metribuzin application in the corn-soybean rotation. However, both weed control and yield were reduced in the wheat-soybean rotation. Most of the metribuzin remained at the 0–5 cm depth, and dissipation was exponential. The mean metribuzin half-life at the 0–5 cm depth across locations, tillage treatments, application time and rates was 11 days. The metribuzin half-life was 4–19 days following PP application and 3–17 days following PRE application. The metribuzin concentration did not exceed 65 μg kg_?1 at the 5–10 cm or 10–20 cm depths in any treatment, indicating that little metribuzin had leached from the surface soil after PP or PRE application. The finding of a higher metribuzin concentration at 5-20 cm depth in tilled plots than in no-till could be attributed to higher initial soil concentrations in the absence of crop residue.     

Measurement and simulation of the movement and degradation of atrazine and metribuzin in a fallow soil

The movement and persistence of atrazine and metribuzin, in a sandy loam soil following application in spring, was simulated using two models. The first model, based on the physical laws describing water and solute movement and using measured values of soil hydraulic properties, underestimated herbicide mobility in the soil and predicted too rapid drying of the deeper soil layers. The accuracy of the simulations was improved by empirically reducing the measured hydraulic conductivities by a factor of 4. This probably reflects the difficulties of obtaining reliable measurements of soil hydraulic properties. A second and simpler model, which simulated water and herbicide movement using mobile and immobile water categories, accurately predicted soil water contents. It tended to underestimate herbicide movement at short times after application, and to overestimate movement later in the experiments. A comparison of different methods of simulating herbicide degradation showed that prediction of degradation rates in the field from laboratory data can be unsatisfactory with some compounds.     

复合改性粘土对除草剂2,4-D的控制释放作用研究

采用无机/有机复合改性粘土作制剂载体,探讨了其对阴离子型除草剂2,4-D的控制释放作用,目的在于延长2,4-D的持效期,同时减轻其污染.利用无机和有机改性的结合优势,复合改性粘土具有更强的吸附性能,能够显著延缓2,4-D在水中和土壤中的释放.分析其水中释放动力学数据得出,2,4-D释放50%所需时间(t_(50))长达73.8 h,远大于有机改性粘土作载体时的1 h.土壤层释放实验表明,当2,4-D载药量在20～80 mg/g之间时,复合改性粘土均能保持良好的控制释放效果.     

Influence of formulation on triticonazole solubilisation and sorption in a soil–water system

The effect of agronomic doses of three suspension concentrate formulations and two anionic surfactant adjuvants on the solubilisation and sorption characteristics of triticonazole fungicide in a loamy clay soil was investigated. Soil sorption of [¹⁴C]triticonazole alone, in the formulations, and in the presence of increasing doses of formulation additives was measured using the classical batch equilibration technique. Triticonazole solubilisation in water‐formulation systems was also evaluated using a batch procedure, and sorption of the formulation aqueous phases on soil was examined. Solubilisation of triticonazole in the formulation systems occurred in excess of the solubility in water (S_w). This was attributed to triticonazole association with surfactant monomers. Sorption isotherms of triticonazole with diluted surfactants and other formulation additives were similar to that of triticonazole alone. We concluded that in soil‐formulation systems, triticonazole solubilisation in excess of the S_w may increase the amount available in soil solution for plant absorption. However, triticonazole molecules preferentially associated with the soil surfaces, and the presence of diluted amounts of the formulation adjuvants would not significantly affect the soil sorption process. © 2000 Society of Chemical Industry