Optimization of Biological Applications with High-Performance Momentive Adjuvants for Tank-mixes and In-can Formulations

Biological solutions have emerged as a promising alternative to traditional agrochemicals, but they still face common challenges such as achieving sufficient spray deposition, coverage, and resistance to wash-off. The use of Silwet™ and AgroSpred™ adjuvants from Momentive's portfolio notably enhances the efficacy of biological spray mixtures. These organosilicone based adjuvants significantly enhance deposition and coverage while reducing the necessity for high spray volumes. This approach enables the treatment of more hectares per tank, ensuring a more reliable and sustainable application for challenging crops. Momentive adjuvants exhibit compatibility with biofertilizers, biostimulants, biochemicals, and a wide array of microbial agents used in crop protection and/or nutrition, making them ideal partners for biologicals.

How Momentive adjuvants work and their benefits for biologicals

The role of an adjuvant can be explained in three simple steps: stick, spread, and penetrate. Based on organosilicone chemistry, Silwet adjuvants offer superior levels of deposition, spreading, and resistance to wash-off via stomatal penetration, or by protective film formation (Figure 1). These significantly boost the efficiency of biologicals, surpassing what is typically achieved with conventional adjuvants.

Figure 1: Key benefits of Momentive’s adjuvants for all types of biologicals.

Superior Deposition: The role of the dynamic surface tension

Dynamic surface tension (DST) plays a crucial role in the adhesion of spray droplets to leaf surfaces ^{[1; 2]}. Generally, a lower DST improves droplet adhesion by reducing the risk of bounce-off and droplet shattering, ensuring more reliable spray applications, thereby minimizing waste (Figure 2).

Figure 2: The effect of Silwet adjuvants on dynamic surface tension (DST) minimizes the risk of bounce-off and droplet shattering, ensuring better adhesion of spray droplets to leaf surfaces.

Figure 3 demonstrates that adding Silwet 408 (A) or Silwet Optim (B) together with Pseudomonas chlororaphis significantly reduces the dynamic surface tension (DST) of the spray solution.

Figure 3: Effect of two Silwet adjuvants on dynamic surface tension of Pseudomonas chlororaphis tank-mixes - (A) Silwet 408 and (B) Silwet Optim.

Optimal coverage: Super-spreading

Momentive's organosilicone super-spreaders enhance spray coverage on difficult to wet foliar surfaces (Figure 4). 

Figure 4: Super-spreading within ca. 30 seconds. When compared to conventional adjuvants (left), Silwet adjuvants can offer up to 10 times more spreading (right).

Just as with agrochemicals, it is essential to evaluate the impact of biological formulations on spreading. Figure 5 illustrates how a Pseudomonas chlororaphis (P.c.) formulation affects the spreading of Silwet 408 and Silwet Optim. Silwet 408 + P.c. behaves similarly to Silwet 408 alone (A), while Silwet Optim + P.c. exhibits reduced spreading compared to Silwet Optim alone (B), though still higher than the biological alone. This highlights the importance of testing tank-mix combinations to achieve the desired coverage.

Figure 5: (A) Effect of adjuvants at different concentrations (% v/v) on spreading (30s) of Pseudomonas chlororaphis (Pc.) - (A) Silwet 408 and (B) Silwet Optim. Pc. contained no less than 1x106 CFU/g of product (use rate was 0.46 wt%).

Likewise, as seen in Figure 6, all Momentive adjuvants significantly improved spreading on crop leaves compared to biological solutions alone. 

Figure 6: Performance of Momentive’s organosilicone super-spreaders (100 μL) with selected biologicals on grape leaves. Biological formulations were used at their recommended dose. Pictures were taken ca.30 seconds post-application, with spreading areas contoured for clarity.

Resistance to wash-off: stomatal infiltration or film formation

Silwet adjuvants minimize the risk of treatment loss due to rain or irrigation shortly after application by facilitating enhanced stomatal penetration of systemic biologicals (Figure 7) or the formation of a protective film for contact biologicals (Figure 8). These key benefits help minimize treatment waste, ensuring the optimal effectiveness of biological agents, which ultimately leads to improved yield and crop quality.

Figure 7: Silwet adjuvants enable rapid uptake of systemic bio-pesticides through stomatal infiltration, ensuring effective protection against wash-off when needed. The concentration of Silwet adjuvants in the tank-mix solution can control this process.

Figure 8: Effect of Silwet STIK-2 film former adjuvant (0.2%) on wash-off resistance of Pseudomonas chlororaphis spray solution (1%) after a 9mm rain on cabbage leaf. This trial utilized a 1% UV-blue dye to demonstrate the efficacy of the adjuvant post rain. The high resistance to wash-off is highlighted by the fluorescence observed on the leaf treated with Silwet STIK-2, even after the rain.

Explore Momentive’s adjuvants toolbox for biologicals

Momentive offers an excellent portfolio of high-quality adjuvants for biocontrol spray applications, including specialized uses such as soil treatments ^[3] and ultra-low volume applications like drone spraying (Table 1). Momentive adjuvants, such as Silwet super-spreaders, can boost the performance of biologicals beyond what conventional adjuvants can achieve, whether in tank-mix or in-can situations. They also support sustainability and regenerative farming with organic listed and biodegradable products. Choose Momentive adjuvants to deliver the best results for your biological solutions.

Table 1: Momentive’s Adjuvant Offerings for Biologicals.

(1) Biodegradability after 28 days - OECD 301B

(2) In-can for pH range of 6.5-7.5. In-can dose rates range from 5 to 20% wt/v.

(3) In-can stability: Silwet HS-312 (pH 3-12) and Silwet HS-604 (pH 4-10). In-can dose rates range from 5 to 20% wt/v.

Compatibility with a wide range of biological solutions

Understanding the compatibility between adjuvants and biologicals is crucial. Silwet adjuvants underwent compatibility testing with multiple microbial products (fungal and bacterial), determining the biological index (BI) for fungi, spore germination for endomycorrhiza (Germ.) and colony forming units (CFU) for bacteria. Overall results indicated a broad range of compatibility of microbes with several Silwet adjuvants (Table 2). 

Table 2: Compatibility studies of Silwet adjuvants with microbial pesticides and biofertilizers.

Classif. (Classification): Toxic (T); moderately toxic (MT); greater than 66 – compatible (C).  

BI (Biological index) values: 0 to 39 – toxic (T); 40 to 66 – moderately toxic (MT); greater than 66 – compatible (C).  

CFU (Colony-Forming Unit) values: 0 to 1.1x10⁵ CFU/g – toxic (T); 1.1x10⁵ to 1.1x10⁷ CFU/g – moderately toxic (MT); 1.1x10⁷ to 9.9x10⁹ CFU/g – compatible (C).  

Germ. (Germination) is measured and compared to a control treatment that was not treated with Silwet adjuvant. NS represents no significant difference from the control, which translates into compatibility.  

*With Silwet Power, the endomycorrhiza was exposed to a concentration of 0.1% v/v. All tests with Silwet Power were conducted at a concentration of 0.05% v/v.

n.t. - Not tested.

Momentive has also conducted a long-term compatibility study on two co-formulants, Silwet HS-604 and Silwet HS-312, designed specifically for in-can applications with a wider pH range. The aim was to assess their impact on the viability of two common biological control agents, Bacillus subtilis and Bacillus pumilus, contained in a distinct commercial liquid formulation. The results demonstrated that both adjuvants were compatible with the SC formulations containing Bacillus species for up to six months. Bacterial concentrations remained consistent from 0 hours to 6 months (Figure 9), indicating sustained viability over the study period.

Figure 9: Histogram of bacterial counts under all tested conditions after 0 hours, 24 hours, 2 weeks, 1 month, 3 months, and 6 months of incubation at 20°C. Both commercial SC formulations had an average pH of 5. Silwet HS-604 and Silwet HS-312 were tested at concentrations of 0.5% and 5% v/v. Bacterial concentration is expressed in CFU/mL.

Field case studies

The efficacy of combining Silwet and AgroSpred adjuvants with various biological products was tested to explore their potential enhancements in yield, disease management, and pest control (Figure 10). Overall, treatments containing the adjuvants gave an increase in microbial efficacy relative to the standard treatments. Additionally, the spray volume was reduced by 25% (400 to 300 L/ha; Figure 10A) and by 40% (500 to 300 L/ha; Figure 10B) for treatments using Momentive adjuvants.

Figure 10: Four efficacy trials showing the enhanced efficacy of microbial-based biologicals with Silwet and/or AgroSpred adjuvants. DAT/DA= days after treatment/application. RF= Microbial pesticide alone. Different letters indicate significant differences at 5%. Note: In the tomato (A) and pepper (B) trials, Momentive adjuvants allowed for a reduction in water spray volume by 25% and 40%, respectively, compared to RF.

Concluding remarks

Momentive adjuvants significantly improve the efficiency of various biological types by:

• Demonstrating compatibility with a diverse range of biofertilizers, microbial pesticides, and biochemicals, whether in tank-mix or in-can scenarios;

• Enhancing deposition and spray coverage by reducing surface tension beyond typical surfactants;

• Enabling a reduction in water spray volume while improving application effectiveness;

• Enhancing penetration, as needed, and improving resistance to wash-off through film formation, allowing for less reapplications after rain, resulting in a more flexible spray scheduling;

• Offering biodegradable options and listings for organic farming (such as OMRI, Ecocert, and Kiwa) products.

Overall, Silwet adjuvants play a crucial role in optimizing the performance of biologicals for foliar and/or soil applications, whether through conventional spray methods or drone application, thereby contributing to a more environmentally friendly and sustainable agriculture.

To learn more about how Silwet and AgroSpred adjuvants can improve your biocontrol products, just scan the QR code below to re-watch our recent webinar on biologicals.

Leading the Future: Momentive's Innovative Support for Agricultural Solutions

Momentive's dedication to innovation ensures its agricultural solutions remain at the forefront, as it is continuously expanding its compatibility data on various biological types and developing new solutions. This includes not only adjuvants as shown in this article, but also high-performance antifoam solutions. These are crucial in fermentation processes commonly used with microbial-based biologicals and aid in controlling foam issues during both the manufacturing process and field applications. For free samples, technical data sheets, or further information, please contact your local Momentive representative or reach out to us at commercial.services@momentive.com.

REFERENCES

¹. Stevens, P.J.G., Kimberley, M.O., Murphy, D.S., & Policello, G.A. (1993). Adhesion of spray droplets to foliage: The role of dynamic surface tension and advantages of organosilicone surfactants. Pesticide Science, 38, 237-245.

². Gaskin, R.E., Elliott, G.S., & Munro, J.P. (2000). Adjuvant technology to reduce spray application volumes on potatoes. Brighton Crop Protection Conference - Pests and Diseases, 2, 687-692.

³. Langendorf, B., et al.; (2024) Advancing Sustainable and Regenerative Agriculture with Momentive's Soil Adjuvants. AgroPages: [web document] AgroPages-Advancing Sustainable and Regenerative Agriculture with Momentive's Soil Adjuvants-Agricultural news

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