Adjuvants 101: Understanding What is in Your Sprayer Tank

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Adjuvants 101: Understanding What is in Your Sprayer Tank

Adjuvants 101: Understanding What is in Your Sprayer Tank

Share this Article

Adjuvants 101: Understanding What is in Your Sprayer Tank

Understanding what is in your sprayer tank before you begin spraying is the most important aspect in management of a pest. Preparation of the pesticide spray solution happens in the sprayer tank where the right amount of pesticide is measured and placed into the tank and thereafter the tank is filled with water.

Starting with the selection of the best pesticide product for the pest you want to control, the ensuing step is the careful dilution of the concentrated pesticide formulation with water prior to application. 

In many instances, applicators must address aspects that are specific to the pesticide or application characteristics. To address those concerns, the applicator needs to add something extra in the sprayer tank. 

What is that “extra” ingredient in your tank?

Most applicators often add an adjuvant to the sprayer tank during the mixing process to address a situation related to the pesticide or application site.

An adjuvant is a chemical substance that is added to the sprayer tank that contains the pesticide you want to apply. The purpose of adding an adjuvant is to:

  1. Modify the activity of the pesticide, e.g., improve the emulsifying, dispersing, wetting, or other property of the liquid pesticidal spray.
  2. Modify the application characteristics, e.g., help prevent pesticide spray drift, condition water, and improve compatibility of mixtures

Importance of Using Adjuvants

  • Helps provide good coverage and retention of pesticide spray on target pests.
  • Modifies the rate of evaporation of pesticide spray to ensure uptake by the targeted pest.
  • Helps retain pesticide spray on target pests in conditions where there is heavy dew, rainfall, or when sprinkler irrigation is used.
  • Enhances penetration and translocation of pesticide which results in improved performance.
  • Adjusts pH of spray solution to overcome mildly alkaline conditions found in some water and on pest surfaces.
  • Enhances coverage of target pests for improved control.
  • Enables the compatibility of mixtures of pesticides with liquid fertilizers, for example, in simultaneous applications.
  • Ensures safety to the crop by making pesticides less phytotoxic to the crop.
  • Reduces drift by thickening the spray solution to increase viscosity of spray droplets which ensure that the pesticide hits the intended target pest.

Classifying Adjuvants

There are a variety of adjuvants and pesticide products available for all types of pest infestation scenarios. A clear understanding of adjuvant and pesticide interactions is necessary for the correct choices to be made that will maximize pest control.

For starters, adjuvants are divided into three broad categories: 

  • Activator adjuvants
  • Spray modifying adjuvants
  • Utility modifying adjuvants

Why should you use an activator adjuvant?

  • Activator adjuvants increase the biological activity beyond what you would get when the pesticide is used alone.
  • Activator adjuvants are particularly useful when applying herbicides.
  • There are five types of activator adjuvants. These are:

  1. Surfactants
  2. Vegetable oils
  3. Crop oils
  4. Crop oil concentrates
  5. Methylated seed oils


  • The term ‘surfactant’ is derived from a surface acting agent.
  • Surfactants improve the surface-modifying properties of liquids, e.g., emulsifying, dispersing, spreading, and wetting.
  • Surfactants are classified as anionic, cationic, ampholytic, and nonionic.
    • Nonionic surfactants are the most often used and chemically inactive when mixed with pesticides.

Vegetable oils

  • Vegetable oils are used as an additive or complete carrier that can be substituted for petroleum-based oil concentrate additives.
  • Vegetable oils can provide enhanced weed control in low humidity and high temperature environments.

Crop oils

  • Crop oils are either mineral or vegetable oils that contain 1 – 2% surfactant.
  • The function of crop oils is similar to surfactants.

Crop oil concentrates

  • Crop oil concentrates are mineral or vegetable oils that contain up to 20% surfactant.
  • Crop oil concentrates enable pesticides to penetrate pest surfaces, while prolonging drying time to facilitate maximum uptake of the pesticide.

Methylated seed oils

  • Methylated seed oils enhance the ability of pesticides to mix with water while promoting penetration of pesticide into target pests.

Why should you use a spray modifying adjuvant?

  • Spray modifying adjuvants are used to modify the spray solution in the tank, on the way to the target pest, or on the target pest itself.
  • There are four types of spray modifying adjuvants. These are:

  1. Spreaders
  2. Stickers
  3. Foaming agents
  4. Thickening agents


  • Spreaders are added to an aqueous spray solution to increase the surface area of the spray droplet on the target.
  • Spreaders are similar to nonionic surfactants.


  • Stickers are added to an aqueous spray solution to cause the spray droplet to adhere to the target surface.
  • The primary function of stickers is to decrease wash-off during rainfall or when irrigating using sprinklers and enhance initial deposition and retention of the spray.

Foaming agents

  • Foaming agents are primarily used to mark spray swath widths.
  • Foaming agents can also be used to enhance herbicide action and to reduce spray drift.

Thickening agents

  • Thickening agents are used to increase the viscosity of the spray solution.
  • The use of thickening agents is essential if you need to reduce pesticide spray drift from the target area.

Why should you use a spray utility modifier?

  • A utility modifier is a type of adjuvant that is used to widen the range of conditions under which a given pesticide formulation is useful.
  • There are four types of utility modifiers. These are:

  1. Antifoam agents
  2. Compatibility agents
  3. Buffering agents
  4. Water conditioning agents

Antifoam agents

  • Antifoam agents are added to the spray solution to decrease or prevent the buildup of foam when the pesticide spray solution is agitated or sprayed.

Compatibility agents

  • Compatibility agents are added to the spray solution to help maintain the mixture of two or more ingredients that would otherwise separate when mixed together.
  • Compatibility agents are commonly used when applying pesticides in combination with liquid nitrogen and fertilizer.

Buffering agents

  • Buffering agents are added to the spray solution to increase the dispersion and/or solubility of a pesticide.
  • Buffering agents are typically used in areas of extremely acidic or alkaline water. The buffering agent will either lower or raise the pH of the spray solution and maintain it at a predetermined level.

Water conditioning agents

  • Water conditioning agents help prevent water antagonism.
    • Water antagonism occurs when a high concentration of double positive charged cations, e.g., Ca++, Mg++, and Fe++, occur in water. When this occurs, the water is referred to as ‘hard water’ and the cations interfere with the performance of many pesticides. 
    • In particular, pesticides that have been formulated in the salt form are impacted the most by hard water and the result is poor pest control.
  • Water conditioning agents react with hard water cations before they can tie up the pesticide.
  • A commonly used water conditioning agent is a product that contains ammonium salts.
    • When added to water, the ammonium salts will dissociate into NH+ ions and negatively charged chelating ions that will seek out and attach to the Ca++, Mg++, and Fe++ ions.
    • The attachment to the positively charged ions prevents them from attaching to the pesticide.
    • The NH+ ions attach to the pesticide but will not interfere with absorption or activity of the pesticide.

Understanding what is in your sprayer tank will:

  • Ensure that you have the best pesticide spray mixture that will control your target pest. 
  • Save you time and money.

Important points to remember:

  1. Select the most appropriate pesticide product and formulation for the pest you are targeting.
  2. Carefully read the pesticide label and look for recommendations for the use of adjuvants with the pesticide.
  3. Determine if the conditions surrounding the application of the pesticide warrants the use of an activator adjuvant, a spray modifying adjuvant, and/or a utility modifying adjuvant.
  4. Select the most appropriate adjuvant product that will ensure that the pesticide spray is delivered to the intended target and provides the desired level of pest control.
  5. Follow the proper guidelines for mixing pesticide and additives in the sprayer tank. 
    • This is an important step that helps ensure that the different chemicals mix well and that the pesticide is not compromised in any way.
    • For more details on proper tank mixing, read The ABCs of Tank Mixing Pesticides

Further Reading on Adjuvants:

Brewer International ( has been a leader in land and water chemistry since the 1980’s and for over 40 years has proudly served it’s national and regional distributors. 

Our products are used widely across the United States in agriculture, aquatics, forestry, rights of way, and land management. 

Our customers trust our dedication to quality ingredients, tried and true formulas, and positive outcomes

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