Solvay's tank mix adjuvant solutions to address emerging and growing trends: Regulations, sustainability, and precision farming

By Denis Bendejacq, Jiamin Wu, Sasha Zavgorodnya, Rachel Li

Tank mixes have long been an integral part of Agricultural practices, evolving over the years to include more and more functionalities. The formats commercially available go from water-based to oil-based dispersions, emulsions or solutions of functional polymers, surfactants and oils. Their value proposition always boils down to making the life of farmers easier, by delivering them with easy-to-use products amenable to their daily operations, whilst providing several attributes in one fell swoop. Drift control, on-target anti-rebound were among the first functionalities to find their way into tank mixes, together with built-in water conditioning and penetration aids to, respectively, ensure the tank-stability of active ingredients, as well as improve their on-target efficacy. From the first launch, in 1996, of natural-based AgRho^® DR2000 – derived guar gum, a versatile natural polysaccharide with remarkable drift reducing and anti-rebound properties - to that, in 2007, of the first emulsion drift reducing agent now used on more than 50+M acres in the US, Solvay has kept on expanding its offer to tackle the many challenges farmers encounter. In the following, we focus on three important needs and trends the Agricultural market is currently facing, and detail how these redefine the design of innovations in the tank mix segment.

Dicamba: Reduction of drift and volatilization. The late 2020 EPA ruling on the use of Dicamba in the United States has imposed anti-volatility agents to be added to the tank in certain proportions to prevent unintended damage to neighboring crops. Buffering agents, such as Potassium Acetate, have shown their ability to considerably limit Dicamba volatility by controlling the pH in the final tank above 5, forcing Dicamba in a form that is far less volatile than it acidic form. The idea to incorporate anti-volatility into the make-up of already existing anti-drift tank mixes, to further ease farmers’ operations quickly gained momentum. Year 2021 has seen numerous products arrive on the market keen on delivering the lowest possible use rate that would successfully pass drift and volatility approval testing by the 3 major Dicamba manufacturers. Other tank mix features may seem secondary in comparison to drift and volatility control that ensure compliance with strict regulation. However, some of these features, such as the resistance to the shear imposed by pump recirculation, remain key to the safe and efficacious use of Dicamba by farmers, especially when the anti-drift technology used is a high molecular weight polymer, such as synthetic poly(acrylamide) or natural guar gum. Poly(acrylamide) provides an control over drift at lower use rates, but is well known to degrade under mixing and recirculation. It is a good candidate to design affordable tank mix adjuvants that disperse easily enough to obtain stable and homogeneous tank formulations, in spite of a necessarily low recirculation (if any at all). Guar gum and its derivative, on the other hand, show superior drift control even after prolonged recirculation, which makes it well suited for complex, multicomponent tank formulations often kept under continuous recirculation, to ensure homogeneous dispersion of all AIs, adjuvants and fertilizers until they are sprayed. Launched in 2021, AgRho^® TripleFx offers an advantageous balance between superior shear resistance as shown in Figure 1, and a reduction of spray drift and Dicamba volatility. It is now approved for use in combination with the 3 major Dicamba manufacturers, in compliance with EPA’s ruling.

Figure 1. Percentage of reduction in driftable fines (fraction smaller than 150 µm) vs number of recirculation cycles through micropump FASCO (type  U62B1, flow rate 3.8 L/min). Composition of the formulation tested 1.4% XtendiMax, 2.27% PowerMax, TripleFx 1.75% v/v. Nozzle: AI11003, pressure: 40 psi.

The race toward tank mixes with increasingly lower use rates has already pushed Solvay’s scientists to explore new options for the design of 2^nd-generation Dicamba-approved tank mixes. These will come to market by the fall of 2022. Regardless of their drift technology, these new prototypes, with additional functionalities, should be beneficial for farmers operations.

Sustainability: Optimized use of Active Ingredients. While the safe use of Dicamba has been the focus of the Americas for the last few years, sustainability is becoming a growing and valuable point of differentiation for tank mix adjuvants. While it encompasses a number of environmental and societal aspects, sustainability is honing more and more in on the responsible and efficacious use by the Agricultural industry of all types of synthetic herbicides, among which glufosinate. As the use of this active continues to grow, it will faces more challenging situations where its efficacy can be improved by designing new classes of tank mix adjuvants for bioactivation. While glufosinate penetrates cuticles, the byproducts of its action, toxic to the leaf tissues, destroy them before the active can reach the vein system. As a result, translocation to other parts of the plant is poor, and high use rates, combined with fine sprays, are needed to ensure maximum coverage. Although built-in surfactant adjuvant combinations (such as sodium laureth sulfate in BASF’s Liberty^®) have shown to significantly improve the potency of glufosinate on grasses and weeds under normal environmental conditions, the combos fall short in arid conditions where water - essential to the efficacy of these classes of surfactant bioactivator - is missing and leaves adapt to form even thicker cuticles. Solvay’s scientists have designed a new type of additive that markedly improves the penetration and performance of glufosinate in dry and hot conditions on grasses (cf. Figure 2a) and, remarkably, on broad-leave plants somewhat taller than typically recommended for the use of Liberty. The solution therefore widens the window of application beyond the point where the herbicide alone will not control tall plants. It provides a long-lasting effect, preventing recovery of the plants at longer times (cf. Figure 2b). Two options are currently in development, one as a direct tank mix adjuvant for users of formulated glufosinate like Liberty^®, and the other, as a built-in option for manufacturers of glufosinate products in search of new innovative options that help push the limits of use of this already important herbicide. While they explore the reapplication of these solutions to other hydrophilic herbicides in challenging environments, Solvay’s scientists are now turning to the challenge of improving the responsible and efficacious use of hydrophobic actives, fungicides, in particular.

Figure 2. (a) Photographs of velvetleaf taken 14 days after: (left) no treatment; (center) treatment with 29 fl oz. Liberty^® (center); (right) 29 fl oz. Liberty^® added with 0.5% v/v of our new-generation adjuvant. Plants were grown in a greenhouse in arid conditions, at a temperature of 30°C and a relative humidity of 30%. (b) Percentage of injury to velvetleaf as a function of the number of days, from the day of application.

The continuous rise of UAV. Drones keep on expanding beyond their initial niche as solutions for high-value crops, or for locations difficult to access. They are becoming more affordable, bigger in size, capacity and autonomy, while showing promising connectivity with real-time monitoring tools and remote control. Their rise as a tool for both precision agriculture and large-scale crops has not only led to new challenges, but also created an entirely new value chain with actors specializing in equipment, digital tools, detection and tracing. For small drones designed to be fully autonomous and rely solely on their own embarked tank, the limitations in how much water, active ingredients and adjuvants can be transported at any given time, impose the use of tank mix adjuvants efficacious at use rates smaller than conventional tank mixes, in the range 0.3-0.5 % v/v, if not less. These tank mixes should be as multifunctional as needed, delivering several benefits in spite of their lower use rate. In 2018, Solvay first launched AgRho^® Aeromate 320 in China, a tank mix specifically designed for aerial applications. In spite of use rates as low as 0.3 % v/v, it proved efficient not only for drift control (by increasing the average droplet size), but also for anti-rebound and wetting (cf. Figure 3, left). Tested on paddy fields with drones, AgRho^® Aeromate 320 also showed improvement in formulation deposition in the vertical direction, regardless of the height (cf. Figure 2, right), which should, in turn, improve efficacy.
Small-embarked tanks imply formulating more concentrated mixtures, sometimes leading with heightened issues in physical instability and incompatibility between AIs and adjuvants, as well as, eventually, clogging of nozzles. Drones equipped with a constant feed of formulation from a mobile formulation tank are explored as a solution, with a potential for longer autonomy, but issues of stability and compatibility will remain, imposing constant recirculation to ensure dispersion and homogeneity necessary to prevent clogging. Whether embarked or not, the need for adjuvants that improve compatibility will undoubtedly be a strong driver for the aerial segment, which Solvay’s scientists are actively working on.

Figure 3. Left: Anti-rebound and wetting efficacy of Drone tank mix AgRho^® Aeromate 320 (0.3 % v/v) and conventional tank mix AgRho^® Starguar (1% v/v), vs. water as a control (high-speed videography of a drop size ~ 2 mm landing on a flowering dogwood tree leaf). Right: superior deposition along the vertical direction of AgRho^® Aeromate 320  vs a blank control. Drone brand: Dajiang MG-1; Nozzle Teejet Flat fan XR11001; pressure 3 bars; Height: 1.5m. Crop: paddy, sprayed with a Indoxacarb 15% + Methoxyfenozide 25% SC, spray dosage: 1L/mu, temperature:  28℃, wind speed: 2-3m/s.

In summary, while tank mixes will likely remain ingredients of choice among rapidly evolving agricultural practices, Solvay’s scientist will constantly adapt their research efforts, and methods, to create innovations that best answer farmers’ needs in compliance with increasingly complex regulations. As part of Solvay’s broad commitment to sustainability, the company vows to deliver on the numerous technical challenges that will undoubtedly emerge from the growth of precision and connected agriculture, and the demand for a responsible use of active molecules.

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

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