Progression of Crop Protection Formulations from Conventional Through Micro-based to Nano Formulations

 Without the use of pesticides, there would be a 78% loss of fruit production, a 54% loss of vegetable production, and a 32% loss of cereal production.¹ As regulatory bodies and consumer pressures demand farmers to reduce environmental damage of agriculture, new strategies for formulations that include nanotechnology, microencapsulation, and improvements in traditional formulations are emerging quickly.

Nanopesticides: Nano Actives and Nanocarriers — Emerging Approach for Ag Formulations

The pharmaceutical industry has been utilizing nanotechnology for many years, and it has now been introduced into the agricultural sector. It is a technology where extremely small nanoparticles are involved. Nanoparticles are small molecules whose sizes range between 1-100 nm and possess many dynamic physical, chemical, thermal, optical, magnetic, and biological properties.

These particles have a large surface-to-volume ratio, and their physicochemical properties differ from the bulk materials. Many scientists believe that further reduction of active ingredients into the nano range or adopting new delivery technology of nanocarriers can significantly boost pesticidal efficacy and efficiency when compared with their conventional pesticide analogs for the following reasons:

1) Smaller sizes increase surface area, leading to more contact with targets;

2) Better and faster penetration/absorption into targets;

3) Less premature loss of pesticides prior to reaching targets.²

In nanoformulations, active ingredients can be used in nano sizes or nanocarriers can be utilized.

Controlled delivery of active ingredient molecules for fertilization and crop protection using nanoengineered nano-capsules (or nanocarriers) is currently the most representative application of nanotechnology in agriculture.³ Nanocarriers can be produced through attrition or synthesis, then target compounds can be embedded into the carrier.

Nanos in the Market

In the market, there are already multiple types of nanocarriers available including silicate, polyacrylate polymer, clay, and carbon tubes/graphene. Nanocarriers can deliver important metabolites or nutrients to a specific site at an appropriate time. One example of nanoherbicide is poly (epsiloncaprolactone) nanoparticles encapsulate atrazine, which showed strong control of the targeted species, reduced genotoxicity level, and could also significantly decrease the atrazine mobility in the soil.⁴

Several nanoparticles such as nickel ferrite nanoparticles and copper nanoparticles, have strong antifungal properties and are effectively used in disease management.

For viral infection treatment, chitosan nanoparticles, zinc oxide nanoparticles, and silica nanoparticles are shown to be highly effective while silver nanoparticles are extensively used for their antimicrobial property against a wide range of phytopathogens.⁵

Foliar application of nanofertilizers is the most efficient method that balances nutrient deficiencies and improves crop yield and quality, effectively decreasing the quantity of fertilizer used. Researchers have reported that nanoparticles greater than 10 nm can penetrate via stomata. These fertilizers are considered as smart delivery systems due to their high absorption capability and greater surface-to-volume ratio.⁶

Carbon nanoparticles such as graphene, graphene oxide, carbon dots, and fullerenes, are used for improved seed germination. Some other nanoparticles used in agriculture are zinc oxide, copper oxide nanoparticles, and magnetic nanoparticles. ⁷

Many companies across the globe are working to adopt nanotechnology in agriculture, some of which are start-ups, and a few of them have had commercial successes.

Vive Crop Protection, Inc., a Canadian-based company, focuses on precision delivery systems for crop protection products and fertilizers. The company’s core chemistry is nanotechnology based on acrylate co-polymers called Allosperse. Allosperse is a nanoparticle delivery platform used to help farmers achieve better value extraction by improving crop protection and fertilizer product utilization efficacy.  A known brand using this technology is AZterknot.

United States-based Aqua-Yield utilizes patented nanocarrier technology that binds fertilizer or crop protection molecules for better adhesion and penetration into targets. This technology, NanoPro and NanoN+, can be added to products as in-can adjuvants or used in a tank mix.

Nanotechnology is still in the very early stages of development, and only few companies, as listed above currently have products in the market.  It is also much more applicable to small, chemical molecules, than microbials, which sizes are usually 300-5,000 nm, so significantly above nanoparticles sizes of 1-100 nm.

Microencapsulation – Step above Traditional Formulations

In the recent years microencapsulation (CS) had been gaining in popularity. CS formulations are typically used for toxic and labile active ingredients, which are encapsulated by a polymeric shell material, not only to improve user safety by decreasing exposure, but also to improve pesticide efficacy by regulating the release rate and protecting sensitive active ingredients from various environmental factors, such as sunlight.

For example, there are many commercial CS products available on the market for pendimethalin, not only to improve the handling, but also to achieve better field efficacy by controlling the release rate. Famous brands are Alcance Sync^TEC from FMC and Stomp from BASF.

Depending on the nature of the polymeric shell material, some of them can even provide adhesion properties to stay on the spray target better, thus reducing rolling down and pesticide loss due to rain wash.

Although CS formulations have much improved efficacy in comparison to other conventional formulations, the particle size of the encapsulated active ingredients are still in the micron sizes, which negatively impacts their penetration into the plants.

 Traditional Formulations – Getting More Efficient and Safer

The goal of pesticide formulation is to enhance the effectiveness of the pesticide’s active ingredients while minimizing the environmental consequence and ensuring safety for both farmers and consumers. These formulations can be dry (e.g., wettable powders (WP) and water dispersible granules (WDG) or liquid (e.g., suspension concentrate (SC) and emulsifiable concentrate (EC)).

There is a general perception that WPs are easy to produce, but are dusty, while WDGs have fewer dust problems, but are more challenging to produce and can have issues with granule disintegration.

Liquid formulations, on the other hand, are typically easier to apply and often contain built in adjuvancy through addition of adjuvants.

In the past decade, SCs have gained popularity overcoming many challenges, including crystal growth formation, active ingredient degradation, and shelf-life instability. ECs are still extremely popular in many regions due to their ease of production and application. However, as leaves burn in hotter climates and regulatory scrutiny to moves away from volatile solvents, there is pressure for manufacturers to move toward other formulations.

One fundamental issue for traditional pesticide’s formulations is the extremely low efficacy. According to Zhao, et al.,⁸ less than 0.1% applied conventional pesticide is utilized by target crops/insects due to spray drift, rolling down, dust drift, leaching and pesticide degradation.

Significant effort had been made over the last years to improve quality and efficacy of traditional formulations, including safer and more efficient inerts to increase actives loading, plant adhesion and penetration as well as increased safety to environment and applicators.

There had been slow but steady reduction in the use of WP and EC formulations, with more focus on the SC (water based) and WDG (granular to reduce dusting). As inerts often create over 90% of the formulation, with the new microplastics ruling in Europe, there is visible trend toward biobased and biodegradable inerts to reduce environmental impact.

More progress should be expected in the coming years, with even faster development of more efficient formulation technologies with inerts, which provide better performance of active ingredients, significantly reduced use rates, improved efficacy, and increased safety, as the agricultural industry progresses toward even more advanced technologies like microencapsulation and nanotechnology.  •

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Photo of Mariola Kopcinski courtesty of Ingevity
Photo of Guigui Wan courtesy of Ingevity and Chengshuai
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References:

1. Tudi, M., Daniel Ruan, H., Wang, L., Lyu, J., Sadler, R., Connell, D., … & Phung, D. T. (2021). Agriculture development, pesticide application and its impact on the environment.International journal of environmental research and public health, 18(3), 1112.

2. Wang, D., Saleh, N. B., Byro, A., Zepp, R., Sahle-Demessie, E., Luxton, T. P., … & Su, C. (2022). Nano-enabled pesticides for sustainable agriculture and global food security. Nature nanotechnology, 17(4), 347-360.

3. Prasad, R., Bhattacharyya, A., & Nguyen, Q. D. (2017). Nanotechnology in sustainable agriculture: recent developments, challenges, and perspectives. Frontiers in microbiology, 8, 1014.

4. Takeshita, V., de Sousa, B. T., Preisler, A. C., Carvalho, L. B., Santo Pereira, A. D. E., Tornisielo, V. L., … & Fraceto, L. F. (2021). Foliar absorption and field herbicidal studies of atrazine-loaded polymeric nanoparticles.Journal of Hazardous Materials, 418, 126350.

5. Panáček, A., Kolář, M., Večeřová, R., Prucek, R., Soukupová, J., Kryštof, V., … & Kvítek, L. (2009). Antifungal activity of silver nanoparticles against Candida spp. Biomaterials, 30(31), 6333-6340.

6. Hong, J., Wang, C., Wagner, D. C., Gardea-Torresdey, J. L., He, F., & Rico, C. M. (2021). Foliar application of nanoparticles: mechanisms of absorption, transfer, and multiple impacts.Environmental Science: Nano, 8(5), 1196-1210.

7. Baz, H., Creech, M., Chen, J., Gong, H., Bradford, K., & Huo, H. (2020). Water-soluble carbon nanoparticles improve seed germination and post-germination growth of lettuce under salinity stress.Agronomy, 10(8), 1192.

8. Zhao, X., Cui, H., Wang, Y., Sun, C., Cui, B., & Zeng, Z. (2017). Development strategies and prospects of nano-based smart pesticide formulation. Journal of agricultural and food chemistry, 66(26), 6504-6512.