Stepan Company: Naturally Derived Adjuvants for Effective Drone Application

Date:04-27-2022

Shrikant Aherkar
Lead Scientist, Stepan Agricultural Solutions – Asia Pacific

Conventional spraying methods, like using a manual knapsack sprayer, is common in Asia due to fragmented land ownership, diverse cropping patterns and labor availability. Asia accounts for 80% of smallholder farmers worldwide with China, India and Southeast Asia accounting for approximately 388 million farms¹. Many of these smallholder farmers use manual sprayers on their fields, which poses significant challenges to the farmer including, speed (manual spraying covers approximately one hectare per 12 hours), imprecise application and potential health hazards. In addition, farm labor is becoming scarce and expensive. In response, many farmers are turning to newer application methods.

The application of pesticides using drones has become popular in Asia, particularly in China², due to cheaper application cost compared to manual spray, better efficiency (covering the same area 30 times faster than manual spray), improved operator safety, less water consumption and almost comparable efficiency against the manual spray³. As a developing technology, drone application can have several challenges including drift to off-target surfaces, stability of the spray dilution at higher concentrations, compatibility of multiple pesticide formulations in a single spray and clogging of the nozzle.

Adjuvants for Drone Application

Tank mix adjuvants can help control drift and improve application properties like wetting, spreading and penetration, while additionally accounting for the lower water level and higher formulation loading needed for drone applications that can negatively affect physicochemical properties. Stepan Agricultural Solutions elected to focus on tank mix adjuvants based on the potential of tank mixes developed for conventional application to be modified for drone application through the use of adjuvants. This approach saves agrochemical formulators from needing to develop separate formulations for drone application, which also negates the need to have new registrations or meet other related regulatory requirements.

Our initial product offerings in this area include STEPGROW^® MP-ADJ and STEPGROW DSD. The former is a versatile multi-functional adjuvant proven to improve drift reduction, wetting, spreading and deposition properties. STEPGROW MP-ADJ is the ideal choice for formulators looking to improve performance at a lower dosage.

STEPGROW DSD is methyl ester-based adjuvant designed to solve issues with drift, sticking and deposition. Methyl ester-based adjuvants are commonly used in the industry and formulators looking for better drift reduction at the same application rate and similar chemistry would do well with STEPGROW DSD.

To ensure that we meet the formulation needs for drone application, Stepan conducted lab and field testing to assess the performance of these two adjuvants in real world applications.

Testing Method

Stepan’s study evaluated our tank mix solutions along the parameters of compatibility, stability, drift, droplet size distribution, foam, spreading, contact angle, surface tension and field trial performance. A market Tebuconazole 430 g/l SC formulation was used as the control. STEPGROW^® DSD and STEPGROW MP-ADJ were compared to the parameters noted in Table 1 against the control and market benchmarks. Drone applications were run using a dilution rate of 225 ml Tebuconazole 430 g/l SC in 15l water. STEPGROW MP-ADJ and its benchmark were tested between 0.1% (15 ml) and 0.2% (30 ml) rate, whereas STEPGROW DSD and its benchmark were tested at 1% (150 ml) dosage.

Formulation and Adjuvants:

· Tebuconazole 430 g/l SC

· Industry market benchmarks

· STEPGROW DSD (naturally derived methyl ester-based adjuvant)

· STEPGROW MP-ADJ (alcohol ethoxylate and natural oil-based extract adjuvant)

Table 1. Parameters tested for drone adjuvant study

Sr. No.	Parameters	Method / Instrument
1	Dispersibility	Visual observation
2	Stability (24 Hours)	Visual observation
3	Cold storage stability (-15⁰C)	Visual observation
4	Particle / droplet size	Bettersize 2000S (laser particle size analyzer)
5	pH tolerance (pH 3 – 9)	pH meter
6	Foam control	CIPAC MT 47.2
7	Droplet size distribution	Bettersize 2000S (laser particle size analyzer)
8	Surface tension	Du Nouy method - surface tensiometer
9	Contact angle	Data-physics model # OCA 20
10	Crop safety / phytotoxicity	Visual observation
11	Efficacy in the field	Crop and pesticide related China local methods

Each parameter signifies the specific application conditions. Dispersibility and 24-hour stability are important to check the compatibility of the adjuvant. In most of the cases, no significant negative effect was observed. All dilutions successfully passed through the 38µ sieve within 2 minutes as per the dispersibility test. For the 24-hour stability test, STEPGROW MP-ADJ and its market benchmark demonstrated similar performance, whereas STEPGROW DSD outperformed its market benchmark. pH tolerance under acidic and basic conditions was observed in all the spray dilutions.

The critical parameters in this study were the droplet size and droplet size distribution.

Test Results

Illustrated in Figures 1 and 2 are the improved performance of STEPGROW MP-ADJ and STEPGROW DSD for droplet size and distribution compared to industry benchmarks. Droplet size increased significantly against control and market benchmarks. The droplet size distribution was also tested using water sensitive papers at three different levels — upper, middle and lower — in the paddy during the drone application field trials. These results also supported the lab data of improved performance using STEPGROW DSD.

Figure 1. Droplet size and droplet size distribution lab study for STEPGROW MP-ADJ

Figure 2. Droplet size and droplet size distribution lab study for STEPGROW DSD

Both adjuvants effectively reduced the surface tension and contact angle of the spray dilution (Figure 3). Along with the comparative studies in the lab, field trials were also conducted on rice paddies with no negative effect being observed in the initial results. Further field studies are in progress.

Figure 3. Contact Angle Lab Study

Further standalone studies focused on crop safety were conducted using STEPGROW MP-ADJ on sensitive crops. Testing on strawberry, okra, cucumber and tomato demonstrated the product to be safe across all crops noted, regardless of stage of growth, when used as recommended.

The table below summarizes the results of all the parameters tested, based on the comparative data gathered, and highlights the improved effectiveness that can be achieved for drone spray applications using STEPGROW MP-ADJ and STEPGROW DSD.

With Tebuconazole 430 g/l SC (225 ml/ 15L)	Alcohol ethoxylate and natural oil-based extract adjuvant			Methyl ester-based adjuvant
	STEPGROW MP-ADJ		Market Benchmark	STEPGROW DSD	Oleic Acid Methyl Ester	Market Benchmark
Test Rate	0.1%	0.2%	0.1%	1.0%	1.0%	1.0%
Compatibility	Excellent	Excellent	Excellent	Excellent	Excellent	Excellent
Drift Control	Excellent	Good	Insufficient	Excellent	Excellent	Good
Wetting	Good	Excellent	Moderate	Good	Good	Moderate
Spreading	Excellent	Excellent	Good	Excellent	Good	Good
Crop Safety	Excellent	Excellent	Good	Excellent	Excellent	Excellent

Stepan Agricultural Solutions is cultivating excellence. Our in-house formulations experts and global manufacturing network are dedicated to helping the agricultural industry address its agrochemical needs. We are committed to providing innovative products that have outstanding performance and unique sustainability benefits. We deliver a complete line of products including, but not limited to, adjuvants, dispersants, green solvents, emulsifiers and specialty blends. Our Stepan Agricultural Innovation Center in Winder, U.S., demonstrates our commitment to liquid and dry formulation design, strategic partnerships, education and sustainable agriculture. In addition, our global R&D teams continue to expand our technological capabilities for organic farming, biologicals and microplastics alternatives.

REFERENCES

1. Working with Smallholders. IFC Sustainable Business Advisory.

2. https://news.agropages.com/News/NewsDetail---38284.html
   

3. https://m.ofweek.com/im/2021-08/ART-201930-8420-30519163.html
   

This article will be published in AgroPages '2022 Formulation & Adjuvant Technology ' magazine to be published this May.

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