STEPGROW^® DSD, A Low-Foam and Spreading Drone Tank-Mix Adjuvant for Solid Formulation Pesticides

Jason Chen

Market Manager, Stepan Agricultural Solutions – Asia Pacific

The Challenges of Spray Solid Pesticide Formulations Through Drones

Drone applications continue to gain popularity in the agriculture industry based on the ability of this advanced technology to provide enhanced safety, precision application and improved efficiency.¹ The successful adaption of liquid formulations for use in drone applications has also proceeded rapidly to meet the needs of growers. Conversely, the adaption of solid pesticide formulations has not proceeded as rapidly due to a range of formulation limitations. From the grower perspective, this is not ideal, as wettable powder (WP) and water dispersible granules (WG) remain irreplaceable in some fruit, vegetable and field crop applications.

When looking at solid formulations in drone applications, a range of potential limitations include:

• High-foam

• Lack of solubility/poor dispersibility

• Compatibility issues with other pesticides and fertilizers

• Particles may clog spray nozzles

• Limited wetting/spreading properties to achieve desired distribution
  

The Risk of High-Foam Level

High-foam level is highly important but is an easily overlooked risk to effective application. High-foam may overflow from the application system and result in environmental pollution, wastage or costly pesticide, equipment damage and potential chemical exposure during the preparation and loading process. It can also reduce pesticide dispersibility, affecting the continuous spraying, and ultimately reducing the efficacy, of the application.

Stepan Agricultural Solutions developed a novel tank mix adjuvant, STEPGROW^® DSD. Supported by years of laboratory development and field trials, this product is a natural oil-based adjuvant that finds utility as a tank-mix and in-can adjuvant. Studies have demonstrated excellent drift control, spreading and deposition properties when compared against alternative adjuvants in drone pesticidal applications. The recommended use rate is 0.5–1.0% (v/v) when used as a tank-mix adjuvant.

Additional benefits of STEPGROW DSD include the ability to improve pesticide compatibility as well as outstanding control of foam levels in the tank.

Laboratory Studies Comparison

To demonstrate that STEPGROW DSD is a suitable solution for use with solid pesticide formulations when sprayed by drones, Stepan screened several mainstream pesticides and compared their foam level, surface tension and compatibility against market benchmark spray and organic silicon adjuvants. Selected pesticide dosages and water volume were based on recommended drone application practices.

Chlorantraniliprole 35% Water Dispersible Granules

Chlorantraniliprole is a systemic insecticide that delivers rapid activity, high insecticidal potency and long-lasting control against most chewing pests on rice, fruits and vegetables crops when used at low dosages. Surface tension analysis of the Chlorantriliprole 35% WG determined a value of 70.5 mN/m, which is high and may suggest that the product alone may not effectively spread and be retained on the rice leaves.

As illustrated below, addition of tank mix adjuvants effectively reduce the surface tension to improve the performance properties of the formulation. All tested tank-mix adjuvants reduce the surface tension below the rice leaves surface tension (36.7 mN/m) and achieve desired wetting and retention properties. The laboratory tests are based on 75g of Chlorantraniliprole 35% WG in 15L of water.

Analysis of foam height shows product differentiation with STEPGROW DSD at both 0.5% and 1.0%. In both cases, the foam remains very low throughout the testing compared to untreated control application (UTC) and competitive alternatives (see Figures 1 and 2).

Figure 1. Foam level and surface tension tests of Chlorantraniliprole 35% WG.

Figure 2.  The initial foam levels of Chlorantraniliprole 35% WG.

Diflubenzuron 25% Wettable Powders

Diflubenzuron is a widely used insecticide to selectively control caterpillars and weevil larvae in forest and field crops. Laboratory studies have shown STEPGROW DSD, when tested at two different dosage levels of 0.5% and 0.1%, exhibited very low initial foam levels compared to the market benchmark and organic silicon adjuvants. An additional tank-mix adjuvant is required as the surface tension of Diflubenzuron 25% WP alone is 40.4 mN/m. All tested tank-mix adjuvants can reduce surface tension and achieve desired wetting and retention properties (see Figure 3). Laboratory tests are based on 135 g of Diflubenzuron 25% WP in 15 L of water.

Figure 3. Foam level and surface tension tests of Diflubenzuron 25% WP.

Imidacloprid 70% Water Dispersible Granules

Imidacloprid is a systemic insecticide that provides excellent control and longer protection against a variety of sucking pests on rice, cotton, fruits and vegetables crops. An additional tank-mix adjuvant is required for Imidacloprid 70% WG due to its extremely high-surface tension at 71.1 mN/m. All tested tank-mix adjuvants can reduce surface tension and achieve desired wetting and retention properties (see Figure 4). Laboratory tests are based on 60 g of Imidacloprid 70% WG in 15 L of water.

STEPGROW DSD showed lower initial foam levels compared to the market benchmark and organic silicon adjuvants. Competitive adjuvants retained higher and persistent foam levels for 30 minutes after tank-mixing.

Figure 4. Foam level and surface tension tests of Imidacloprid 70% WG.

Mancozeb 75% Wettable Powder

Mancozeb is a broad-spectrum contact fungicide on many crops against wide varieties of disease complexes. STEPGROW DSD at two different dose levels of 0.5% and 1.0% showed lower initial foam levels and are comparable with the market benchmark at 1.0%. In addition, the organic silicon adjuvants remained persistent at higher foam levels after tank-mixing. Mancozeb 75% WP alone may not be able to spread on the rice leaves and provides full protection properly as its surface tension is 36.9 mN/m. All tested tank-mix adjuvants can reduce its surface tension and achieve desired wetting and retention properties (see Figure 5). Laboratory tests are based on 2,250 g of Mancozeb 75% WP in 15 L of water.

Figure 5. Foam level and surface tension tests of Mancozeb 75% WP.

Tricyclazole 75% Water Dispersible Granules

Tricyclazole is a highly systemic fungicide used to control blast incidence that occurs at various growth stages of rice crops. STEPGROW DSD at two different dose levels of 0.5% and 1.0% showed lower foam levels that were better and/or comparable to the market benchmark. Alternatively, foam level for the UTC and organic silicone adjuvant treatments remained persistently high, even after 30 minutes.

Tricyclazole 75% WG and all tank-mix adjuvant treatments performed within a low-surface tension range of 25.2–32.4 mN/m (see Figure 6). Laboratory tests are based on a use rate of 375 g of Tricyclazole 75% WG in 15 L of water.

Figure 6. Foam level and surface tension tests of Tricyclazole 75% WG.

Compatibility and Dispersibility Evaluations

All tests showed that STEPGROW DSD, the market benchmark and organic silicon adjuvants either maintained or enhanced the solution compatibility for the tested solid pesticide formulations. The one exception noted is all tested tank-mix adjuvants provided manageable compatibility performance when sprayed with the Mancozeb 75% WP through drone applications as Mancozeb 75% WP has a high-loading at 15% w/v.

In addition, all adjuvant tank-mixed pesticides showed excellent dispersibility with no visible particles, agglomeration or flocculation during the assessments.

Drift Control Capability

Based on our previous studies on liquid pesticide formulations, STEPGROW DSD contributed to drift control by enhancing the Tebuconazole 430 SC droplet size and distribution compared to UTC and market benchmark (See Figure 7). Data for the solid pesticide formulations are still being generated.

Figure 7. The droplet size distribution of Tebuconazole 430 g/L SC with different tank-mix adjuvants.

The use of STEPGROW DSD as a tank-mix adjuvant for drone application of solid pesticide formulations exhibits good foam control, reduces surface tension and enhances compatibility and dispersibility. STEPGROW DSD is a powerful solution for applicators when used at a dosage of 0.5–1.0% (v/v).

Stepan Agricultural Solutions is dedicated to cultivating innovative and sustainable solutions to help formulators and growers address their formulation concerns. We actively look to cultivate strategic partnerships based on creative problem solving and customized solutions.

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Reference:

¹The Role of Drone Technology in Sustainable Agriculture, Global Ag Tech Initiative, May 25, 2021