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Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
Microbio Tank-Mix Adjuvant Overview from Lamberti
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Microbio Tank-Mix Adjuvant Overview from Lamberti

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Microemulsion, alkyl poly glucoside, tank-mix, adjuvant

Microemulsion, alkyl poly glucoside, tank-mix, adjuvant

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  • 1. MICROBIO: A NOVEL MICROEMULSION AS AN EFFICIENT TANK-MIX ADJUVANT FOR HERBICIDE TREATMENTS Alberto Colombo, Gianfranco Paganini and Peter Bohus Agro-Chemistry Laboratory; Cesalpinia Chemicals (Lamberti Group); Via Piave, 18 - 21041 Albizzate (VA), Italy SUMMARY A new microemulsion adjuvant for tank mix application containing: fatty acid esters from transesterification of vegetable oils, anionic ester of alkylpolyglucoside and ethoxylated fatty alcohols was developed. Physico-chemical properties were optimized to improve stability, synergism amongst components and compatibility with various pesticide formulations. Surface tension and particle size were measured; rheological characterisation of the adjuvant was carried out to verify microemulsion physical status and stability. This adjuvant mixture was designed to quickly wet and spread droplets on the leaf in order to get a uniform spray deposit over foliage surface. Wettability and spreading on specific surfaces were also determined. Biological efficacy in weed control of various tank-mix blends of the adjuvant with commercial herbicide formulations was studied. Three herbicide/weed combinations of Microbio as tank mix adjuvant were examined: one water soluble herbicide (Bentazone Na salt) applied on black nightshade; two water insoluble actives (Nicosulfuron and Quizalofop-P-ethyl) applied on wild oat. Key words: microemulsion, alkylpolyglucoside, tank-mix. INTRODUCTION Fatty acid esters from transesterification of vegetable oils, alkylpolyglucosides and ethoxylated fatty alcohols have individually been widely used as tank-mix or built-in adjuvants for herbicides. They are valuable because of the following properties: improvement of biological efficacy of active ingredients, excellent versatility and ease of use in combination with various formulations of actives, application technologies and crop varieties. In addition, they can replace adjuvants which are harmful to the environment, such as nonylphenol ethoxylates or fatty amine ethoxylates. Recently, a new class of anionic esters of alkylpolyglucoside have been described as novel tank-mix adjuvants (1,2), which appear to have good potential as adjuvants in agro-chemistry. Microemulsion is a highly effective physical form of agrochemical delivery system, which combines stability of complex formulations, performance and easy handling. We have developed a stable microemulsion (Microbio® from Cesalpinia Chemicals SpA, Italy) containing a citric ester of alkylpolyglucoside, fatty acid esters from transesterification of a vegetable oil and an ethoxylated fatty alcohol, which proved to be a higly effective adjuvant with different herbicide actives.
  • 2. METHODS AND MATERIALS Wettability and Surface Tension Analysis of static surface tension (EST) was performed using a Sigma 70 tensiometer (KSV Instrument Ltd) on the adjuvant mix diluted in water at different concentrations at 25°C (ISO 304, ISO 4311). Wetting power of aqueous spray was evaluated at 25°C by determining the sinking time of a cotton diskette, using an internal method based on DIN 53901. Spreading Dynamic contact angle, as a function of time, was studied using a Rycobel PG-X goniometer at different concentrations of Microbio on a glass plate (ASTM D-724). Particle Size Analysis Was carried out using a N4 Plus Nanosizer (Coulter) at 20°C with the following parameters: refractometric index (n=1.433), density (d=0.98 kg/dm3 ) and viscosity (η=40 mPa.s), which are characteristic of Microbio. Scanning was performed at different angles with 360 sec run time. Rheological Characterisation Rheological profile was studied with Advanced Rheometer 2000 (TA Instruments), using a double gap geometry. Viscosity of Microbio was measured as a function of temperature (from 0° to 70°C) and shear rate (from 1 s-1 to 400 s-1 ). Rheograms of shear stress vs shear rate (under steady state flow) and of ln η vs T-1 were obtained. Biological Efficacy Trials (carried out by SurfaPlus bv, Wageningen, NL) Plant material Black nightshade (Solanum nigrum L.; Bayer code SOLNI) and wild oat (Avena fatua L.; Bayer code AVEFA) were grown in a growth chamber under 14 hrs of light, at 18/12 (±0.5)°C (day/night) temperature, and in 70/80 (±5)% (day/night) relative humidity. Light was provided by high-pressure mercury lamps and fluorescent tubes to give 70 W/m2 (PAR) at leaf level. The plants were grown in 11 cm diameter plastic pots filled with a mixture of sand and humic potting soil (3) (1:2 by volume). The pots were placed on a sub-irrigation matting, which was wetted daily with a half-strength nutrient solution. After emergence, the black nightshade and wild oat plants were thinned to one and five plant(s) per pot, respectively. Black nightshade was treated at the four-leaf stage and wild oat was treated at the 2-3 leaf stage. Herbicide application Treatment solutions were applied with an air-pressured laboratory track sprayer having 1.2 mm nozzles fitted with a perforated (0.6 mm) whirling pin and delivering 200 L/ha at 303 kPa. The adjuvants Microbio and Hasten® (emulsifiable esterified rapeseed oil from Victorian Chemicals) were added at 0.25% (v/v). Herbicide formulations used were: Bentazone (Basagran® from BASF); Nicosulfuron (Milagro® from Syngenta); Quizalofop-p-ethyl (Targa Prestige® from Bayer). Measurement of herbicide performance The fresh weight of the aerial parts of black nightshade and wild oat was determined as a parameter of herbicide performance.
  • 3. Experimental design and data analysis Experiments were conducted with four replicates per experiment, according to a completely randomized design. The data of the adjuvant tests were subjected to analysis of variance using the Genstat statistical package (Release 6.1; Rothamsted Experimental Station). The means of each treatment were compared according to Fisher’s LSD (0.05). LSD (0.05) is the Least Significant Difference between mean values at the 5% level. RESULTS AND DISCUSSION Wettability and Surface Tension Aqueous spray of Microbio show better wetting properties than a corresponding emulsifiable vegetable oil. A lower surface tension and sinking time with the microemulsion system were obtained (Table 1 and 2). Table 1: Static surface tension of aqueous solutions at 25°C Surface tension (mN/m) 0.2% Surface tension (mN/m) 0.5% Microbio 31.1 29.3 Emulsifiable vegetable oil 33.5 31.5 Ethoxylated Alcohol 27.0 26.7 Alkylpoly Glucoside Ester 25.8 25.5 Table 2: Sinking time of a cotton diskette in 0.25% w/w of aqueous spray at 25°C Water Microbio Ethoxylated alcohol Emulsifiable vegetable oil Alkylpoly Glucoside Ester Ethox. NF Time (sec) > 300 110 5 182 25 5 Spreading Spreading of aqueous dilutions of Microbio was determined in comparison to a solution of ethoxylated fatty alcohol, as a function of time (Table 3). Fig. 1: Contact angle determination vs time In agreement with the effect of surfactants on surface tension and contact angle reported in the literature (4), it can be seen in Fig. 1 that, within the range considered, the higher the concentration of Microbio (curves group marked A), the lower the contact angle measured. This finding is analogous to the behaviour typical spreading adjuvants (curves group marked B).
  • 4. Particle Size Analysis Particle size analysis (Table 3) suggests a droplets distribution of Microbio (detected only at high deviation angles) that falls within the microemulsion range (5). Table 3: Particle size of Microbio measured at 25°C (expressed in nm) Angle Medium diameter Standard deviation 21.3° Not detectable --- 64.6° 31.0 13.2 90.0° 25.7 11.7 Rheological Characterisation The flow curve of Microbio (Fig. 2) indicates a Newtonian behaviour (a general feature of low viscosity microemulsions) (6). From the linear curve of Fig. 2, viscosity was found to be independent of shear rate and equal to 44.8 mPa.s. Fig. 2: Flow curve of Microbio at 25°C Thermodynamical parameters were calculated from a rheogram of ln η vs T-1 (Fig. 3) using equation 1 (6): (eq. 1) With eq. 1, values of ∆H and ∆S were calculated, from which ∆G was obtained, as reported in Table 4. The thermodynamic parameters derived from rheological studies suggest an intrinsic stability of Microbio, as reported in literature for similar system (6). y = 0,0438x + 0,0113 y = -3E-06x + 0,0448 1,00E-03 1,00E-02 1,00E-01 1,00E+00 1,00E+01 1,00E+02 0,1 1 10 100 1000 Shear rate (1/s) ShearStress(Pa) shear stress viscosity shear stress interpolation viscosity interpolation ( ) RT H R S V hN hNR S RT H hNhN RTG ∆ +    ∆ −=     = ∆ − ∆     =∆    =∆ lnln ln ln RT Gln η ηυ ηυηυ
  • 5. Fig 3: rheogram of ln η vs T-1 Tab. 4 Biological Efficacy Tests As detailed in Methods (see above), Microbio was tested on Black nightshade (Solanum nigrum L.) and Wild oat (Avena fatua) in combination with three herbicide active ingredients: Bentazone (Basagran from BASF); Nicosulfuron (Milagro from Syngenta); Quizalofop-P-ethyl (Targa Prestige from Bayer). Our new adjuvant was compared at the same concentration of 0.25% (v/v) in water to a well known commercial adjuvant (Hasten, from Victorian Chemicals, Australia). Results are reported in Fig. 4 (A, B, C). Fig. 4, A Fig. 4, A shows the effect on Black nightshade at two dosages of Bentazone. (20 and 40 g/ha). Microbio and Hasten have a dramatic effect on herbicide efficacy at the lower sub-optimal dosage of 20 g/ha. Fig. 4, B shows the effect on Wild oat at two dosages of Quizalofop-P-ethyl (2 and 6 g/ha). Microbio shows a slight better effect on herbicide efficacy than Hasten at the lower sub-optimal dosage of 2 g/ha. Infuence of adjuvants on bentazone efficacy (SOLNI) 0 5 10 15 20 25 Untreated Bentazone 20g/ha(BE- 20) BE-20+ Microbio BE-20+ Hasten Bentazone 40/ha(BE- 40) BE-40+ Microbio BE-40+ Hasten FW 16 DAT (g) LSD(0.05)=2.31 Sample controlled variable ∆∆∆∆H ∆∆∆∆ S ∆∆∆∆G (298K) (kJ/mol) (J/K*mol) (kJ/mol) Microbio Shear Stress 35.6 -61.5 53.9 Evaluation of ∆∆∆∆ H e ∆∆∆∆ S y = 4281,1x - 17,414 -4,5 -4 -3,5 -3 -2,5 -2 - 1,5 -1 -0,5 0 0,00305 0,0031 0,00315 0,0032 0,00325 0,0033 0,00335 0,0034 0,00345 0,0035 0,00355 1/T (K -1 ) ln(viscosity) viscosity measures interpolation
  • 6. Fig. 4, B Fig. 4, C Fig. 4, C shows the effect on wild oat at two dosages of Nicosulfuron (5 and 15 g/ha). Microbio shows a similar effect on herbicide efficacy as Hasten at the lower sub- optimal dosage of 5 g/ha. CONCLUSIONS We have developed a mixture containing three components, each one displaying individual adjuvant activity in combination with herbicides. Therefore, a carefully balanced microemulsion of the three ingredients shows excellent stability, synergism amongst components and compatibility with various pesticide formulations. Rheological profile and thermodynamic parameters confirm the microemulsion physical status of the mixture, which appears to also have good spreading and wetting properties. These properties should translate in ease of use and effectiveness in actual field applications, Biological efficacy trials in weed control with various tank-mix combinations of the adjuvant with different herbicide active ingredients applied on Black nightshade or Wild oat, at a constant concentration of 0.25% (w/w) in water, showed that at all hebicide dosages tested, Microbio showed either an equal or better efficacy than a reference commercial adjuvant. Our novel microemulsion adjuvant combines the advantages of eco-friendly components with long term storage stability, easy handling and good biological efficacy. Infuence of adjuvants on nicosulfuron efficacy (AVEFA) 0 5 10 15 20 25 Untreated Nicosulfuron 5g/ha(NIC- 5) NIC-5+ Microbio NIC-5+ Hasten Nicosulfuron 15g/ha(NIC- 15) NIC-15+ Microbio NIC-15+ Hasten FW 21 DAT (g) LSD(0.05)=2.58 Infuenceof adjuvantsonquizalofop-P-ethyl efficacy(AVEFA) 0 5 10 15 20 25 Untreated Quizalofop-P-ethyl2g/ha (QUIZ-2) QUIZ-2+Microbio QUIZ-2+Hasten Quizalofop-P-ethyl6g/ha (QUIZ-6) QUIZ-6+Microbio QUIZ-6+Hasten FW21 DAT(g) LSD(0.05)=2.78
  • 7. REFERENCES 1. Bohus, P., Colombo, A.; 2004. Proceedings of 7th International Symposium on Adjuvants for Agrochemicals, Cape Town, SA pp 301 – 306 2. European Patents n° EP 510564 3. Soil no. 12, Colent b.v. , Lent, The Netherlands 4. Singh, M., Orsenigo, J.R., Shah, D.O.; 1984. JAOCS vol 61 n°3 pp 596 - 599 5. Tadros, T. F.; 2005. Applied Surfactants; Wiley-VCH; Weinheim pp 309 – 311 6. Acharya, A., Ghosal, S.K., Moulik, S.P., Subramanian, N. et al.; 2005. Chem. Pharm. Bull. vol 53(12) pp 1530 –1535. Acknowledgements We wish to thank Dr. Hans de Ruiter for very helpful suggestions and collaboration.

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