Adjuvants 101: Understanding the “Extras” in Your Tank
So, you’re ready to make an application. It’s time to apply an herbicide, or maybe a pesticide, insecticide or fungicide, and you want to ensure you’re getting the most out of every droplet that leaves the sprayer.
Are you including an adjuvant in your tank mix? How do you know if you should?
An adjuvant is a non-pesticide product added to a spray tank mix that enhances the performance of the spray solution. They often improve spray mix characteristics – such as spreading, penetration or droplet size – or reduce any potential application problems from the spray mix itself, thus increasing effectiveness. Examples of adjuvants include surfactants, oils, buffers, and defoaming agents.
Spray adjuvants can be categorized into two groups: Activator adjuvants and special purpose adjuvants.
1. Activator Adjuvants
Activator adjuvants improve the action of a pesticide product. These improvements encourage absorption and efficacy. Surfactants, oils and nitrogen-based fertilizers all fall into this category.
Surfactants change the surface tension of a spray droplet. They make the area of pesticide coverage larger, increasing exposure to the chemical. These are useful when applying a pesticide to a plant with waxy or hairy leaves.
Some commonly used surfactants include:
Nonionic Surfactants: - Compatible with most pesticides - Help pesticide sprays penetrate plant cuticles - Are recommended for most pesticides that require a surfactant
Organo-silicone Surfactants: - Reduce surface tension, increase spreadability and improve rainfastness
Crop oils promote the penetration of a pesticide spray either through a plant's waxy cuticle. Two commonly used variations are:
Crop oil concentrates (COCs) have the penetration of an oil with the spread of a surfactant. COCs are often used with post-emergence herbicides.
Vegetable oil concentrates (VOCs), in many cases, have gone through a process called esterification, which results in a methylated seed oil (MSO). MSOs work similarly to COCs to increase penetration of the pesticide.
Adding ammonium sulfate (AMS) or urea-ammonium nitrate (UAN) to a spray mix has been shown to increase the efficacy of some herbicides. Many times, these are available in easier-to-mix liquid forms, which provide more consistent results.
2. Special Purpose Adjuvants
Special purpose adjuvants correct conditions that can affect the spray solution or application negatively. By controlling these factors, pesticide performance can be optimized. This group of adjuvants includes:
Most pesticides perform best in slightly acidic spray water with a pH of 4.0 to 6.5. Those in solutions above pH 7.0 are at greater risk of breaking down. Buffers lower the pH of spray water and help stabilize it at a constant level.
Hard water minerals can bind with active ingredients in some pesticides, decreasing pesticide performance. Water conditioners neutralize these minerals and protect the spray mix from this problem. Many conditioners will also include a buffer.
Some pesticides can create foam in spray tanks, often because of the use of a surfactant or the spray tank agitation system. This can be reduced by adding a defoaming agent.
Stickers increase the ability of particles to stick to a surface, decreasing the amount of pesticide that washes off during irrigation or rain. They can also reduce pesticide evaporation and slow degradation of pesticides by UV rays.
Drift Control Agents
Drift control agents improve the placement of pesticide sprays by increasing droplet size, a priority near sensitive sites or when conditions require caution.
When used with special equipment, these adjuvants produce foam to mark where a product was applied, helping avoid missed or overlapping areas.
Tank cleaners work with water and oil-soluble pesticides and are often recommended by pesticide labels.
But How Do You Know Which to Include in Your Mix?
Most pesticide labels will include a section to help you decide what type of adjuvants will help you get the most out of your application. They’ll utilize language such as “required,” recommended,” or “can be used” to help you understand which adjuvants are essential to your mix and which ones are optional.
For example, the label for Sharpen® herbicide indicates that for optimum burndown, an MSO plus an AMS or UAN must be used. It states that an NIS cannot be used as a substitute for the MSO; an AMS is specifically recommended when mixing with a glyphosate-based herbicide.
Before using any adjuvant, always read and follow the accompanying pesticide or other product label. Not all adjuvants are labelled for use in all states, and many adjuvants have crop specific recommendations as well. Violating these instructions is an illegal use of the pesticide and can result in crop damage or poor performance.
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1. Hock, Winand (2015) Spray Adjuvants; Retrieved from https://extension.psu.edu/spray-adjuvants
2. Witt, James M. (2012) Agricultural Spray Adjuvants Retrieved
Sharpen® is a registered trademark of BASF.
ALWAYS READ AND FOLLOW LABEL USE INSTRUCTIONS. It is a violation of federal and state/provincial law to use any pesticide product other than in accordance with its label. The distribution, sale and use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. It is your responsibility to confirm prior to purchase and use that a product is labeled for your specific purposes, including, but not limited to, your target crop or pest and its compatibility with other products in a tank mix. This information should not be used as a replacement for consulting the applicable product label. Consult the label for the most complete and up-to-date information about any referenced product. Readers must have a valid applicator license to use restricted use pesticides. Please consult your state department of agriculture for complete rules and regulations on the use of restricted use pesticides, as some products require specific record-keeping requirement.