Adjuvant in Herbicide: Uses, Types & Tips

Adjuvant in Herbicides Overview

• Adjuvants in herbicides can help improve postemergence herbicide performance and modify spray solution characteristics.
• Herbicide product labels outline specific instructions for the use of adjuvants.
• Adjuvants in herbicides must be properly matched to each product formulation and tank mixture for optimum effectiveness and crop safety.

What is the function of adjuvants in herbicides?

Adjuvants play an important role in herbicide formulations and spray mixtures to help herbicide performance either by improving herbicide activity or ease of application. Herbicide labels are the most important source of information for adjuvant recommendations that cover diverse use situations and tank mixtures. Adjuvants are specific for each product as researched and developed by the herbicide manufacturers.

• Adjuvants include spreaders, stickers, wetting agents, penetrants, stabilizing agents, compatibility agents, buffering agents, anti-foam agents, and others. ¹

Since herbicide spray adjuvants impact how much herbicide enters the plant, they can impact weed control and crop safety; therefore, it is important to follow the label requirements for each herbicide.

What is the difference between activator adjuvants and utility modifiers?

• Adjuvants can be classified into two main groups: Activators and utility modifiers (or special purpose adjuvants).

• Activator adjuvants, such as surfactants, crop oil concentrates (COC), and nitrogen (N) are normally used to help improve the performance of herbicides by increasing herbicide retention or penetration on or into leaf surfaces, improving rainfastness, or to decrease photodegradation of herbicides.²

• Utility modifiers, such as buffering, antifoam, and drift control agents, typically modify the characteristics of the spray solution and product compatibility.

What are the Types of Adjuvants in Herbicides?

Adjuvants in herbicides play a critical role in improving herbicide performance, spray coverage, and crop safety. Selecting the right adjuvant depends on the herbicide formulation, tank mix, and environmental conditions. Below are the main types of adjuvants commonly used in agricultural applications.

Nonionic Surfactants (NIS)

Non-ionic surfactants are widely used herbicide adjuvants that improve plant coverage and herbicide penetration. They help herbicides spread evenly on leaf surfaces and enhance uptake while being generally low in crop toxicity. Non-ionic surfactants are suitable for most foliar-applied herbicides and are an essential component in achieving optimal weed control.

Methylated Seed Oil Surfactant (MSO) and Crop Oil Concentrates (COC)

Oil-based adjuvants like MSOs and COCs are designed to improve herbicide penetration into leaf surfaces by reducing surface tension.

• Crop Oil Concentrates (COC): Derived from petroleum, they enhance herbicide absorption and may increase weed control effectiveness.

• Methylated Seed Oils (MSO): Derived from seed oils, MSOs function similarly to COCs but are plant-based.

These adjuvants are particularly useful under adverse conditions such as drought or hard water. However, they may increase the risk of crop injury compared to surfactants, so proper rates and label instructions must be followed.

High Surfactant Oil Concentrates (HSOC)

HSOCs are emulsifiable oil-based adjuvants containing 25–50% surfactant in at least 50% oil. They combine the benefits of oil and surfactants, providing improved herbicide coverage and penetration. HSOCs can be based on either MSO or COC and may increase crop injury risk if not used according to product labels.

Ammonium Nitrogen Fertilizers

Certain nitrogen fertilizers can serve as adjuvants when applied at recommended rates, improving herbicide activity under challenging conditions. Common examples include:

• Spray-grade ammonium sulfate (AMS)

• Urea ammonium nitrate (UAN)

These fertilizers enhance herbicide uptake in hard water, cool temperatures, or drought-stressed crops, and can be particularly effective in tank mixtures.

Anti-Foaming Agents and Other Utility Modifiers

Utility modifier adjuvants alter the characteristics of the spray solution or improve tank mix compatibility. Examples include:

• Buffering agents: Maintain spray solution pH for optimal herbicide activity.

• Anti-foaming agents: Reduce foam formation during spraying.

• Drift control agents: Minimize spray drift in windy conditions.

While these adjuvants do not directly enhance herbicide activity, they can help with application consistency, crop safety, and tank mix stability.

Are adjuvants always required?

Each herbicide product has adjuvant requirements that are specified on the product label. The label will provide guidance and adjuvant options to address tank mixtures, environmental conditions, or weed species characteristics. Some herbicide products, such as Roundup WeatherMAX® Transorb® II Technology liquid herbicide, are formulated with sufficient adjuvants in the herbicide formulation and may not need additional adjuvants added to the spray mixture. Some products have specific recommendations for spray adjuvants that the user must add to the spray mixture.

What environmental factors affect adjuvant performance?

The effectiveness of herbicide adjuvants can vary depending on environmental conditions at the time of application. Growers should consider weather, water quality, and crop stage to ensure optimal herbicide performance and crop safety.

Key environmental factors include:

1. Temperature

• High temperatures can increase herbicide volatilization, reducing efficacy.

• Some adjuvants, particularly oil-based products (COC, MSO, HSOC), can help improve herbicide uptake under cooler conditions by enhancing leaf penetration.

• Western Canada: Cooler spring temperatures may reduce herbicide activity, so growers often rely on oil-based adjuvants or ammonium fertilizers to boost uptake.

• Eastern Canada: Warmer early-season conditions usually require less aggressive adjuvants, but high heat can increase crop stress, making careful adjuvant selection important.

2. Humidity

• Low humidity can increase droplet evaporation and reduce herbicide retention on leaves.

• Surfactants and stickers help maintain spray coverage and droplet adhesion in dry conditions.

• In humid conditions, herbicides may run off leaves more easily, so proper adjuvant selection helps reduce wash-off and improve absorption.

3. Rainfall

• Rain within a few hours of application can wash herbicides off leaves, reducing efficacy.

• Rainfast adjuvants, such as certain surfactants or crop oils, can help improve herbicide retention during light rainfall.

4. Wind

• Windy conditions can cause spray drift, reducing herbicide deposition on target plants and increasing off-target risk.

• Drift control adjuvants help minimize this risk, particularly when applying post-emergence herbicides.

  
  

5. Water Quality

• Hard water with high calcium or magnesium can reduce herbicide activity.

• Water-conditioning adjuvants (e.g., ammonium sulfate) bind minerals and improve herbicide uptake.

• Western Canada: Hard water is more common in prairie regions, making water-conditioning adjuvants more frequently needed.

• Eastern Canada: Water tends to be softer, so growers may rely more on surfactants and oil-based adjuvants than mineral-binding agents.

6. Crop and Weed Stage

• Younger, actively growing weeds often absorb herbicides more readily.

• Some adjuvants are more effective at particular weed growth stages or for certain weed species. Explore growth stages for corn, soybean, canola and cereals.

• Labels provide guidance on matching adjuvants to both crop and weed conditions for optimal control.

  
  

Tip for Growers: Always consult the herbicide label to select the adjuvant that is most appropriate for your region, crop, and current environmental conditions.

How Do I Know Which Adjuvant to Use?

Conclusion

Herbicide adjuvants play a critical role in improving spray coverage, uptake, and overall weed control while maintaining crop safety. Understanding the types of adjuvants (such as surfactants, crop oils, and ammonium nitrogen fertilizers) and how environmental conditions affect their performance can help you make informed decisions for your fields.

Explore Bayer’s range of herbicide products and the Spray Forecasting Tool to find solutions tailored for your crops and adjuvant needs, ensuring effective and safe weed management.

^{For additional information, contact your local Bayer representative.}

^Sources

^{1 Jordan, T, Johnson, B., and Nice, G. 2011. Adjuvants used with herbicides: Factors to consider. Purdue University. https://extension.entm.purdue.edu/pestcrop/2011/issue25/index.html#adjuvant.}

^{2 Curran, W.S. and Lingenfelter, D.D. 2009. Adjuvants for enhancing herbicide performance. Agronomy Facts 37. Penn State Extension. https://extension.psu.edu/.}

^{3 Hartzler, R. 2013. (Re) learning to accept herbicide injury to crops. Iowa State University, https://www.extension.iastate.edu/.}

^{Hartzler, B. 2001. Role of spray adjuvants with postemergence herbicides. Iowa State University Weed Science Online https://crops.extension.iastate.edu/encyclopedia/role-spray-adjuvants-postemergence-herbicides.}

^{Web sources verified 29/6/21.}

^{Legal Statements}

^{ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.}

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