Adjuvants 101: Agricultural Surfactants Yesterday, Today, and Tomorrow

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Adjuvants 101: Agricultural Surfactants Yesterday, Today, and Tomorrow

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Agricultural surfactants are chemical products that are commonly used today to improve performance, yet 70 years ago they were hardly mentioned.

A surfactant, orSURFace ACTing AgeNT, is a type of adjuvant that is designed to improve the dispersing/emulsifying, absorbing, spreading, wetting, sticking, and penetrating properties of a pesticide spray mixture.

An adjuvant is an ingredient that aids or modifies the action of the principal active ingredient.

Agricultural surfactants – yesterday

18th and 19th century

  • Additives such as resins, tar, flour, molasses, and sugar were used to improve the adherence and biological performance of a pesticide active ingredient on the target pest.
  • The first agricultural surfactant was a soap solution that was combined with kerosene and used to kill insects. Soap solution was also combined with arsenical solutions to increase toxicity to weeds.
  • Oil soaps derived from animals, fish, and whales were used to enhance pesticide performance.
  • Sugars and glues were considered to be “stickers” as adjuvant research continued.
    • Stickers are chemical substances that cause the spray droplet to adhere to the target surface. Stickers decrease wash-off during rainfall and enhance initial deposition and retention of the spray.

20th century

  • The modern era of synthetic pesticides began in the 1930s and an initial breakthrough occurred in the 1940s with the introduction of 2,4-D herbicide.
  • Soaps and minerals were replaced by nonionic surfactants.
    • Nonionic surfactants are a type of compound that has no electrical charge and can be readily mixed with any agrichemical.
  • Nitrogen fertilizers, e.g., ammonium sulfate and urea ammonium nitrate were used to enhance herbicidal activity.
  • Glycerin was introduced as a humectant.
    • A humectant keeps the spray deposit moist and in true solution, and therefore extends the time that it is available for absorption.
  • Crop oil concentrates, which reduce the amount of pesticide active ingredient and spray volume applied, were developed.
  • Organosilicone-based surfactants with excellent wetting, spreading, and penetrating properties were developed.

Agricultural surfactants – Today

Agricultural surfactants are classified as activator adjuvants.

  • Activator adjuvants modify some pesticidal spray characteristics, including particle size, viscosity, and evaporation rate to increase pesticide spread, absorption, and rain fastness, and decrease photodegradation.

Further classification of agricultural surfactants

Agricultural surfactants are further classified based on their electrical charge properties as follows:

  • Produce no electrical charge:
    • Nonionic surfactant.
    • Mix readily with any pesticide.
    • Most commonly used agricultural surfactant.
  • Produce a positive charge:
    • Cationic surfactant.
    • Not often used in agriculture
  • Produce a negative charge:
    • Anionic surfactant.
    • Rarely used in agriculture.
    • Commonly used in cosmetics, household cleaners, and domestic detergents.
  • Produce both a positive and negative charge:
    • Ampholytic (amphoteric) surfactant.
    • Rarely used in agriculture.

Agricultural surfactants are used in a variety of compositions to aid pesticide function on targeted pests.These surfactant-containing products are wetting agents and oils.

Wetting agents

  • Wetting agents increase the ability of water to displace air or liquids from the leaf surface, allowing it to be wet by the herbicide. Wetting agents help spread the solution more evenly over the leaf.

Oils

  • Oils increase the retention time of a solution on target pests, which allows pesticide uptake to increase. Oils mostly contain emulsifiers to allow them to mix with water. Oils are basically mineral oils with different contents of surfactant in each formulation (3%–20%) and are further classified as:
  • Crop oils– emulsifiable petroleum oil-based products containing up to 5% surfactant and the remainder is oil.
  • Crop oil concentrates– are emulsifiable petroleum oil-based products most commonly used in agriculture. They contain 5%–20% surfactant and a minimum of 80% oil and are commonly used with herbicide spray applications.
  • Vegetable oils – The base in the formulation is oil from sunflower, soybean, oilseed rape, peanut, or corn, which is combined with surfactants of different content.
    • Vegetable oil concentrates –are emulsifiable vegetable oil products containing 5%–20% surfactant and a minimum of 80% vegetable oil.
    • Modified vegetable oil –oil extracted from seeds that have been chemically modified. Methylated seed oil (MSO) is a modified vegetable oil.
  • Modified vegetable oil concentrate– anemulsifiable, chemically modified vegetable oil product containing 5%–20% surfactant.

Agricultural surfactants – Tomorrow

The global agricultural surfactant market is projected to continue growing for the foreseeable future and the demand that they are environmentally safe products will likely increase. Environmental concerns from the overuse of pesticides will be a driving force for the continued use of agricultural surfactants. The challenge will be for scientists to formulate novel green or environmentally friendly compounds that maintain crop protection.

Concomitantly, the demand for alternative agricultural surfactants based on renewable sources will continue to rise. This will require new surfactants to be based on natural products, such as vegetable oils, lecithin, sugars, amino acids, and others.

Further reading

 

References

Castro, M.J.L., C. Ojeda, and A.F. Cirelli. 2013. Surfactants in Agriculture. Green Materials for Energy and Depollution. Pp. 287-234. (Accessed, August 29, 2022).

Pacanoski, Z., 2015. Herbicides and adjuvants. Herbicides, Physiology of Action, and Safety; Price, A., Kelton, J., Sarunaite, L., Eds, pp.125-147. (Accessed, August 29, 2022).

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