Spray Characterization to Optimize Insecticide Performance. Dow AgroSciences LLC Indianapolis, IN USA

Transcription

1 ILASS-Americas 29th Annual Conference on Liquid Atomization and Spray Systems, Atlanta, GA, May 2017 Spray Characterization to Optimize Insecticide Performance H. Jeon 1, D. Linscott 1, J. Schleier III 2, M. Rushton 2, L. E. Gomez 2, M. Somasi 1,* 1 Actives to Products Research and Development 2 Crop Protection Research and Development Dow AgroSciences LLC Indianapolis, IN USA Abstract Efficacy of crop protection products can be affected by a variety of variables chief among which is spray coverage on the target substrate. Generally speaking, increasing coverage for insecticides via fine droplet sprays leads to better efficacy and lower application rates. However, finer droplets are prone to physical drift through the air, which in turn could lead to off-target crop injury, in the case of herbicides, or runoff leading to a less-than-optimal environmental profile. Therefore, it is critical to characterize the spray tank mix to determine the effect of application conditions (nozzle type, height, pressure, wind, etc.) and the formulation composition (dynamic surface tension, evaporation time, contact angle, etc.) for optimal performance with minimal drift potential. In this work, a generic framework will be presented to understand the key parameters affecting product activity for an insecticide formulation. Under this framework, several agrochemical spray tank mixes were characterized by contact angle, droplet evaporation time, and spray droplet size spectrum in laboratory conditions. These data were then correlated with greenhouse efficacy trials on cotton aphids. Our studies showed that droplet contact angle and evaporation time have the greatest influence in controlling cotton aphids using the example formulation. On the other hand, efficacy was not influenced significantly by the use of low drift nozzles. The technique presented in this work will enable options to optimize efficacy via tank mix adjuvants in combination with specific application conditions to minimize spray drift. * Corresponding author: Madan Somasi, msomasi@dow.com, Actives to Products R&D, Dow AgroSciences LLC., 9330 Zionsville Road, Indianapolis, IN 46268

2 Introduction Efficacy of crop protection products can be affected by a variety of variables, chief among which is spray coverage on the target substrate [1]. Generally speaking, increasing coverage for insecticides via fine droplet sprays leads to better efficacy and lower application rates. However, finer droplets are prone to physical drift through the air, which in turn could lead to offtarget crop injury, in the case of herbicides, or runoff, leading to a less-than-optimal environmental profile. Therefore, it is critical to characterize the spray tank mix to determine the effect of application conditions (nozzle type [2], height, pressure, wind, etc.) and the formulation composition for optimal performance with minimal drift potential [3]. A systemic insecticide (hereafter referred to as active ingredient) that was developed to control sap-feeding insects was evaluated for the efficacy variation on its cotton aphid control as a function of application conditions. A suspension concentrate (SC) formulation containing the active ingredient was selected for this evaluation in foliar application conditions. This formulation will be referred to as GF-3513 in the remainder of this paper. This report includes a detailed study of the physical characteristics of the spray solution (density, viscosity, dynamic surface tension and spray droplet size statistics), the resulting efficacy in biological testing as well as the predicted downwind deposition of the spray to determine potential off-target movement or drift characteristics of the application system. Adjuvants Dyne-Amic (NIS) Hasten (MSO) Silwet L-77 (Organosilicone) Intake Adjuvant (Paraffinic Oil) Tween 20 (Polysorbate 20) Surfer (NIS) Materials and Methods Manufacturer Helena Chemical Company Wilbur-Ellis Company Helena Chemical Company Dow AgroSciences Canada Inc Min/Max Dilution Rate (%, vol/vol) 0.375/ / / /2.000 Croda 0.400/0.800 Dow AgroSciences Ltd (U.K.) 0.250/0.500 Table 1. List of adjuvants and their dilution rates for insecticides. Key adjuvants (additives used to enhance the effectiveness of the product) used with GF-3513 have been summarized in Table 1. Trade names and a short description in parentheses have been included. For example, Dyne-Amic is an adjuvant based on a non-ionic surfactant (NIS). Similarly, Hasten is a methylated seed oil (MSO)-based adjuvant. Spray droplet size spectra were measured for tank mixes of GF-3513 with six adjuvants at two different concentrations, which are listed in Table 1. Dilution rates of GF-3513 were determined corresponding to 100 ppm of the active ingredient with spray volume of 200 L/ha. Physical Characteristics of Spray Solution Physical characteristics of the spray solutions (GF with adjuvant listed in Table 1 in tap water), such as the contact angle, viscosity, density and dynamic surface tensions, were measured to understand physical characteristics of each spray solution, and their impacts on spray droplet sizes. Contact angle (a measure of the wettability of the spray solution) for insecticide solutions was measured by an optical tensiometer (Theta, Biolin Scientific AB, Sweden). A flat aluminum coupon, wrapped with fresh paraffinic film, was used as the deposition surface. A drop (~10 µl) was deposited on this surface using a micro pipette. The drop was allowed to equilibrate for a few seconds, and contact angle measurements were taken: the tensiometer takes the side view images of the deposited drop, detects the surface and calculates the contact angle via the built-in image process algorithm. The average value of the three measurements was reported. Figure 1 shows an example contact angle measurement. The equipment was initialized and calibrated per the manufacturer s recommendation before making any contact angle measurements. Figure 1. Example of a contact angle measurement. Viscosity of the spray solution was measured with a viscometer (DV2T, Brookfield AMETEK, Middleboro, MA USA). A density meter (DMA 4100, Anton Paar GmbH, Graz, Austria) was used to measure density of spray solutions. The density meter was rinsed

3 (Sympatec GmbH, Clausthal, Germany) in a custombuilt spray chamber. The spray droplet size spectrum of each tank mix was measured three times, and the sprayer was cleaned before switching tank mixes to eliminate carryover effects from the residues of the previous spray solution. Spray droplet size spectra statistics, driftable fines (droplet diameter less than 150 µm), Dv0.1 (which indicates 10% of the spray volume is comprised of droplets smaller than this value), volume median diameter (VMD, Dv0.5) and Dv0.9 (90% of spray volume has droplets smaller than this number) were calculated from the measurements. Greenhouse Biological Efficacy Trial The effects of adjuvants and spray droplet sizes on the biological efficacy were tested in a greenhouse study. Juvenile cotton plants (Gossypium hirsutum) were grown in a greenhouse at 26 º C and 50 % relative humidity. The cotton plants were exposed to 1000 watt artificial growth light for 16 hrs a day. Once the plants were matured for efficacy test, each plant was pruned to have similar amount of canopy. Spray solutions were prepared by tank mixing GF-3513 with each adjuvant mentioned previously to evaluate the adjuvant impact on efficacy, and each spray solution was sprayed at spray volume equivalent of 200 L/ha. In addition, each spray solution was also sprayed using all five nozzles to Figure 2. Equipment set for measuring droplet evaporation time. with distilled water and acetone between measurements, and all solution densities were measured at room temperature (20 C). A bubble pressure tensiometer (BP-2, KRŰSS GmbH, Hamburg, Germany) was used to measure dynamic surface tension. Dynamic surface tensions of the spray solutions were measured at room temperature for surface ages from 10 ms to 1000 ms. The evaporation time (an indicator of the relative uptake time for the active ingredient) of the spray solution drop was measured with an automated droplet image system (Figure 2) which consisted of a USB digital camera (DCC1645C, Thorlabs Inc. Newton, NJ, USA) connected to a laptop computer mounted on a lab stand. A custom designed computer program was written to capture the image of a deposited drop every second (example is shown in Figure 2). Paraffinic film wrapped aluminum substrate was used to deposit the drop. The ambient temperature and the relative humidity were also monitored throughout the experiment. Evaporation time was determined as the time point past which there were no changes in the captured images. Droplet Size Spectrum Measurement Tank mixes of the formulation GF-3513 with adjuvants were atomized using several common ag-nozzles. All the nozzles reported in this study were from Spraying Systems Co., Wheaton, IL, USA. The nozzles and the spray pressures were selected such as to obtain a wide range of droplet size spectra (very fine to very coarse) as per ASABE Standard S [4]. Details about the nozzles used can be found in Table 2. The droplet size spectrum for each spray solution was measured using a laser diffraction system, Sympatec HELOS Selected Adjuvants Tween 20 (0.27 %) (Polysorbate 20) Dyne-Amic (NIS, %) Silwet L-77 (0.025 %) (Organosilicone) Blend (0.25 %) (Silwet L-77 and Tween 20) Nozzles (Droplet Size Spectrum) TX6 at 414 kpa (Very Fine) XR8002 at 414 kpa (Fine) AIXR11002 at 414 kpa (Medium) DG9503EVS at 129 kpa (Coarse) AI11002 at 414 kpa (Very Coarse) Table 2. Adjuvant and nozzle selections for greenhouse efficacy study evaluate spray droplet size impact in the efficacy. Spray was applied approximately 20 cm above the cotton plants. Selected adjuvant and nozzle with spray conditions are summarized in Table 3. After spray applications, each plant was infested with 20 to 30 cotton aphids (Aphis gossypii). They were kept in a temperature-controlled greenhouse (at 26 º C), and the number of live aphids was recorded after seven days from the applications. All treatments were repeated twice.

4 Cotton aphid control efficacy data was analyzed with JMP Pro (Ver , SAS Institute Inc., Cary, NC, USA) to understand effects of spray droplet size spectrum and adjuvant in terms of efficacy improvement. AGDISP simulation for predicting spray drift As stated before, biological efficacy needs to be optimized by minimizing off target movement or drift. The drift potential of each of the sprays (formulation-adjuvant-nozzle combination) was modeled using AGDISP (Agricultural Dispersal Ver. 8.26, Continuum Dynamics Inc., Ewing, NJ, USA) spray modeling software, originally developed by the USDA Forest Service to accurately predict the spray deposit over and downwind of the application area. Conditions used to run the modeling software are in Table 3. The four key outputs of the model are Application Efficiency: the measure of how much active material lands on the intended application area. Downwind Deposition: the amount of active ingredient that lands between the edge of the application area and the maximum downwind distance (794 m). Airborne Drift: the amount of active ingredient that remains upward beyond the maximum downwind distance. Carrier Evaporated: the measure of how much spray volume evaporates. Parameters Application Method Meteorology condition Surface Spray Material Application Atmospheric Stability Swath Input/Section Ground Application, Flat fan (Hollow cone is unavailable) at 60 psi and releasing height of 3 ft Single height, 5 mph of wind speed, -90 degree of wind direction, temperature of 23.9 C and RH of 50% Upslope and side slope angle was zero. Canopy height of 1 ft. No changes in surface detail. Water (with Active Fraction of and Sum of Active Fraction and adjuvant fraction was used as Non-volatile fraction) at liter per hectare (20 gallon per acre). DSD (Droplet Size Distribution) was manually imported to modelling software using spray chamber measurements of GF-3513 Overcast. Swath width of 60 ft. Table 3. Application and environment conditions used in AGDISP for running spray deposit simulations Results and Discussion Physical Characteristics of Spray Solution The physical properties of the spray solution described in the Materials and Methods section such as evaporation time, contact angle, viscosity, and density, are summarized in Table 4. In addition, dynamic surface tension at surface age of 1000 ms (hereafter static surface tension due to long surface age) has been included. The adjuvant used along with the formulation to prepare each spray solution is listed in the first column of the table. From the data, one can note that the density of all the solutions is close to that of water. Similarly, the viscosity of the spray solutions is generally similar to that of water and variations are minimal (~3 6 mpa.s). Dynamic surface tension measurements are shown in Figure 3. All the adjuvants reduce the surface tension of the spray solution relative to water. This is expected due to their surfactancy. In addition, the surface tension is a function of the surface age, with the earlier ages (10 ms) corresponding to droplet formation times and later ages (1000 ms) closer to the equilibrium surface tension values. Static surface tensions of the spray solutions were functions of the adjuvant used and demonstrated significant variation (20 47 mn/m). Surface tension of the solutions correlates well with contact angle and evaporation time with limited data set: spray solution with higher surface tension results in higher contact angle and slower evaporation time (Figure 4). Spray solution containing Silwet L-77 proved to be the best spreader with a contact angle too low to measure and a fast evaporation time. On the other hand, solutions with Hasten had the largest surface tension and contact angle with a corresponding slowest evaporation time. Droplet Size Spectrum Measurement Spray droplet measurements were conducted for all different GF-3513/adjuvant mixes at both the low and the high use rates using all five nozzles described previously. Table 5 shows the summary of a typical set of spray droplet measurements from a single nozzle (TX6) for all combinations of GF-3513 and adjuvants. Data using water alone is also shown for comparison. As expected, the TX6 nozzle, a hollow cone nozzle intended for maximizing spray coverage, produces a large fraction of driftable fines (60 to 85%), and the corresponding VMDs are also generally small (95 to 130 μm). The droplet size is influenced by the type of adjuvant used as well. Intake (1 %, v/v) and Surfer (0.5%, v/v) with GF resulted in largest and smallest VMD of μm and 94.7 μm, respectively. Although they have some variations, droplet size spectra from all tank mixes with this given nozzle are classified as very fine droplet spectrum which is same as the manufacturer s classification with water for TX6. Similarly, the effect of changing nozzles can be seen in Figure 6, where the solid line depicts the VMD of GF- 2513/Tween20 (0.27v/v%) spray solution mix for all five nozzles tested. From the figure, it can be seen that the effect of the nozzle can be substantial on the VMD (~100 μm using TX6 to ~400 μm using AI11002).

5 Adjuvants Dyne-Amic (NIS, %) Hasten (MSO, %) Silwet L-77 (Organosilicone, 0.05% v/v) Intake Adjuvant (Paraffinic Oil, 1.0 %) Tween 20 (Polysorbate 20, 0.4 %) Surfer (NIS, 0.5 %) Evaporation time (s) Contact Angle (degree) Viscosity (mpa s) Density (g/cm3) Static Surface Tension (mn/m)** * *Contact angle cannot be measured due to its nature of spreading over depositing area upon deposition. ** Dynamic surface tension at the surface age of 1000 ms. Table 4. Droplet evaporation time, contact angle, viscosity, density and dynamic surface tensions of spray solutions containing GF-3513with each adjuvant listed in the first column GF-3513+Dyne-Amic GF-3513+Silwet L-77 GF-3513+Intake GF-3513+Hasten GF-3513+Surfer Water GF-3513+Tween Surface Age (ms) Figure 3. Dynamic surface tension of spray solution at surface ages from 10 ms to 1000 ms Evaporation time (s) y = x R² = Contact Angle (Degree) y = 1.675x R² = Figure 4. Influence of surface tension in evaporation time and contact angle of spray solution. Solid line in both the plots is the linear trendline.

6 Droplet size (in µm) spectra of GF-3513 spray solutions containing the adjuvant Hasten Silwet L-77 Dyne-Amic Intake Tween 20 Surfer (0.156 v/v%) (0.05 v/v%) (0.625 v/v%) (1.0 v/v%) (0.4 v/v%) (0.5 v/v%) Droplet Size Spectrum of DI water (µm) Dv Dv0.5 (VMD) Dv Driftable fines (%) Table 5. Spray droplet size spectra of GF-3513 with key adjuvants while atomizing with TX6 nozzle at kpa (60 psi). Data with spraying water alone is shown for comparison. Volume Median Diameter (Dv0.5, um) Surfact age of 10 ms 90 y = x R² = Figure 5. Relationship between spray droplet statistics and dynamic surface tension at different surface ages. Solid line in both plots is the linear trendline. Volume Median Diameter (Dv0.5, um) Surfact age of 1000 ms y = x R² = The effect of the dynamic surface tension on the droplet size spectrum can be seen in Figure 5. From the figure it appears that VMD seems to have a slight dependence on earlier surface age (10 ms) dynamic surface tension. As the surface age increases, this correlation appears to vanish. These results imply the static surface tension may not be a good indicator of predicting spray droplet sizes, as the droplet interfaces form very quickly in these spray systems. Due to instrument limitations, no data could be collected at lower than 10 ms surface age. Greenhouse Biological Efficacy Trial Spray efficacy performance was evaluated and aphid control was evaluated at 7 days after application (7DAA). This data has been plotted as a bar graph in Figure 6. In addition to the spray data, this Figure also contains representative VMD data (plotted as a solid line with markers) for GF-3513/Tween 20 spray mix for the various nozzles used in the study. Statistical analysis of the data revealed that the differences of the efficacy at 7DAA were not significantly influenced by spray nozzles (or spray droplet size spectrum). Rather, efficacy improves markedly when adjuvants are used along with GF-3513 in the spray solution. This result shows that for this particular active ingredient, uptake by the plant is the critical aspect of insecticide performance rather than coverage alone, and specific adjuvants appear to work better than other adjuvants or without adjuvant.

7 AGDISP Simulation for Predicting Spray Drift Deposit AGDISP spray deposit prediction and numeric measures for application quality, e.g., downwind deposit, airborne drift, carrier evaporation and application efficacy for GF-3513 with the adjuvants Tween 20 are summarized in Table 6. The corresponding VMD is also Conclusions A framework has been presented for evaluating new agrochemical formulations for efficacy and drift potential. It includes measuring various physical properties of the spray solution comprising the formulation and other tank mix partners such as adjuvants. Part of the physical GF-3513 alone GF Tween 20 (0.27%) GF Dyne-Amic (0.375%) GF Silwet L-77 (0.025%) GF Blend VMDs of GF-3513 with Tween 20 (0.27%) Insect Control (%) Volume Median Diameter (um) 0.0 TX6 XR8002 AIXR11002 DG9503EVS AI11002 Spray Nozzles Figure 6. Cotton aphid control efficacy of insecticide with adjuvant 7 days after application. 0.0 included in this table for reference. The data is qualitatively similar to AGDISP predictions for other spray solutions. From the table, it can be noted that the application efficiency (% of active ingredient hitting intended area) improves with increasing VMD. Similarly, the downwind deposition and airborne drift are inversely proportional to the droplet size. In this particular case, % carrier evaporated appears to have a strong dependence on the nozzle type (67% for TX6 down to 4% for AI11002). This data can then be used in conjunction with the efficacy data from Figure 6 to recommend a nozzle type for optimum efficacy while minimizing off-target movement of the active ingredient. For example, in this case one could potentially recommend the AIXR11002 to provide adequate coverage for quick knockdown control while keeping the drift and downwind deposition to a reasonable level. property data (density and viscosity) is required as input to the measurement of the dynamic surface tension. This is an important interfacial property to describe the droplet formation during the atomization process of spraying. Other parameters of interest are the evaporation time and the contact angle. While the evaporation time gives an indirect estimate of the time available for the active ingredient to penetrate the target substrate, the contact angle is a good surrogate for wettability characteristics of the spray solution. Droplet size spectrum and biological efficacy in the greenhouse were measured, while the potential spray drift of the spray solution was estimated using the AGDISP modelling tool. A developmental insecticide formulation (GF-3513) was used to exemplify the methodology. Six different adjuvants based on various chemistries and five commonly used agrochemical spray nozzles were utilized in this study. The evaporation time and the contact angle were shown to be dependent strongly on the dynamic tension of the longest surface age, which approaches the equilibrium surface tension. The droplet size spectrum

8 Key measures Application Efficiency (%) Downwind Deposition (%) Airborne Drift (%) Carrier Evaporated (%) TX6 XR800 2 Nozzle AIXR DG9503 EVS AI VMD (µm) ASABE, Droplet Size Classification by Droplet Spectra. S572.1 (2009). 5. Teske, M. E. and Curbishley, T. B., AGDISP Version 8.25 User Manual, Continuum Dynamics, Inc (2011). 6. Matthews, G.A., Pesticide Application Methods, 3 rd Ed., Wiley-Blackwell, New York (2000) Table 6. Simulated key measures from different spray was found to have a weak correlation with the dynamic surface tension of the smallest surface age measured. Biological efficacy (7DAA) was found to be a stronger function of the adjuvant used than the droplet size spectrum of the spray solution. Typically, use of an adjuvant to aid in uptake of the active ingredient into the plant helped in increasing the efficacy than using GF-3513 alone. Within the adjuvants tested, Silwet L-77 seemed to lag the others in this particular system because of the small evaporation time associated with its use. As a result, the active ingredient does not have adequate time for complete uptake with Silwet L-77. Finally, AGDISP modeling predictions of the downwind deposition demonstrated the benefit of using low drift nozzles. As the efficacy of the formulation was shown to be not a strong function of the droplet size in this example, this analysis provides the option of using a medium to a coarse spray system to provide adequate control without the need of a very fine spray for maximizing coverage. It should be noted that this might not be true for other formulations where better coverage is imperative for desired performance. Other techniques such as lowering boom height or managing spray volume [6] could also lead to lower drift, but it may not be desirable due to equipment safety or uniform coverage concerns, respectively. The outcome of this work needs to be validated further in larger scale field trials in the future. Similarly, analogous studies should be conducted with other agrochemical formulations based on herbicide and fungicide active ingredients with different modes of action for completeness. References 1. Ishfaque, M., Ashfaq, M. and Sayyed, A.H., Pak. Journal of Biological Sciences, 8: (2005) 2. Derksen, R.C., Zhu, H., Fox, R.D., Brazee, R.D., Krause, C.R., Trans. ASABE, 50: (2007) 3. Campos, H.B.N., Ferreira, M.C., Costa, L.L., Decaro Júnior, S.T. and Lasmar, O., Int. Journal of Ag Research, 9(4): , (2014)

9