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Wednesday, September 8, 2021

Understanding Herbicide Adjuvants

What You’ll Learn...

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

The Function of Adjuvants

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
  • 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.

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. 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® with 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. The user should pay particular attention to label instructions for each tank-mix product because label recommendations for adjuvants may differ for each product. Each herbicide manufacturer may have supplemental labels or fact sheets that provide additional guidance for the use of adjuvants for specific application situations, weed species, crops, or tank mixtures. There is a diverse array of adjuvant products and brands. The user must understand the composition and function of each product, while considering expected environmental conditions at the time of herbicide application, to properly match the adjuvant to individual herbicides or tank mixtures.

Types of Adjuvants

There are several adjuvants that can be used with herbicides such as surfactants, oil concentrates, ammonium N fertilizers, spreader-stickers, wetting agents, and penetrants.1,2,3 Nonionic surfactants (NIS) are good dispersing agents to help improve plant coverage and penetration of foliar-applied herbicides with low toxicity to crop. Oil concentrates help improve herbicide penetration into leaf surfaces and reduce surface tension. Crop oil concentrates (COC) are derived from petroleum. Methylated seed oils (MSO) function like other oil concentrates but are derived from seed oils.2 High surfactant oil concentrates (HSOC) are emulsifiable oil-based products containing 25-50% surfactant (wt/wt) in a minimum of 50% oil (wt/wt). HSOC oil concentrates may be MSO or COC based. COC, MSO, and HSOC, may increase the risk of crop injury more than surfactants.3 Ammonium N fertilizer products, used at recommended rates, can act as adjuvants to help improve the performance of certain herbicides especially under hard water conditions, drought conditions, cool temperatures, or in tank mixtures. Spray-grade ammonium sulfate (AMS) or urea ammonium nitrate (UAN) are common N fertilizer adjuvants. Blended adjuvants contain specific combinations of special purpose and/or activator adjuvants that serve multiple functions.2

Table 1. Adjuvant recommendations for Bayer herbicides.
Herbicide Adjuvant Recommendations
Buctril® M herbicide

No additional adjuvant required

*Vios G3® herbicide must be mixed with a labelled glyphosate or glufosinate herbicide and only used in the respective herbicide tolerant corn.

Converge® XT herbicide
Pardner® herbicide
Puma® Advance herbicide
Roundup Xtend® with VaporGrip® Technology
Thumper® herbicide
Vios G3® herbicide
XtendiMax® with VaporGrip® Technology herbicide
Infinity® herbicide

For control of cleavers at the 4 to 6- whorl growth stage, control of Canada fleabane, volunteer soybean, round-leaved mallow and suppression of giant ragweed and spreading atriplex, add ammonium sulphate (AMS).

AMS Rate:
99% solution: 500g/ha.
49% solution AMS: 1L/ha.
40% solution: 1.25L/ha

Infinity® FX herbicide

For control of Canada fleabane, volunteer soybean up to the 9th trifoliate leaf stage and suppression of giant ragweed and spreading atriplex, add AMS.

AMS Rate:
99% solution: 500g/ha.
49% solution: 1L/ha.
40% solution: 1.25L/ha

Laudis® herbicide Requires external surfactant (Hasten Spray Adjuvant) and nitrogen fertilizer source (28% UAN) to achieve optimum weed control. Use of a spray-grade liquid nitrogen fertilizer is recommended.
Luxxur® herbicide

When Luxxur® herbicide is applied alone, addition of an adjuvant may provide more consistent overall weed control, more consistent control of wild oat in areas of heavy infestation, or more consistent control of Japanese brome.

A labelled non-ionic surfactant Rate: 0.25% AMS (in Spring wheat ONLY). Rate:
99% solution: 500g/ha.
49% solution AMS: 1L/ha.
40% solution: 1.25L/ha.

Do not tank-mix with any other adjuvants, chemical additives or fertilizers unless recommended on the Luxxur® herbicide label. When tank mixing additive/adjuvant with Luxxur® herbicide, minor crop injury may be observed. These symptoms are temporary and do not impact crop yield.

Olympus® herbicide Must be applied in a tank mixture with glyphosate. Glyphosate may be present as isopropylamine, dimethylamine, monoammonium, diammonium, trimesium or potassium salt.
Olympus® liquid herbicide

To be used in conjunction with liquid nitrogen fertilizer (28% UAN) at a rate of 2.5L/ha. Use of a spray-grade liquid nitrogen fertilizer is recommended.

For control of weeds present and control of later flushes of broadleaf weeds and/or annual grasses Option® 2.23 OD herbicide must be tank mixed- see label for tank-mixes.

R/T 540® herbicide, Roundup Transorb® HC herbicide, Roundup WeatherMAX® herbicide At rates of 0.83L/ha or higher extra surfactant is generally not recommended.
Sencor® 480 herbicide, Sencor® 75 DF herbicide

Do not tank-mix with liquid fertilizers, oils, oil concentrates, or surfactants when applying postemergence because severe crop injury may occur.

In no and minimum tillage systems under adverse conditions for improved burndown of small emerged annual weeds:

Crop oil concentrate (Assist): 1% v/v
Non-ionic surfactant at 0.1% v/v
Crop oil, 28-0-0, or 10-34-0 at 5% v/v for tank mixtures with herbicides Dual Magnum® herbicide or Dual II Magnum® herbicide +/- Roundup® Herbicide

Tundra® herbicide

For control of cleavers at the 4- to 6-whorl growth stage, control of Canada fleabane, and suppression of giant ragweed and spreading atriplex, add AMS.

AMS Rate:
99% solution: 500g/ha.
49% solution AMS: 1L/ha.
40% solution: 1.25L/ha

Varro® herbicide

When Varro® herbicide is applied alone, addition of an adjuvant may provide more consistent overall weed control, more consistent control of wild oat in areas of heavy infestation, or more consistent control of Japanese brome.

A labelled non-ionic surfactant Rate: 0.25%
AMS (in Spring wheat ONLY). Rate:
99% solution: 500g/ha.
49% solution AMS: 1L/ha.
40% solution: 1.25L/ha.

Do not tank-mix with any other adjuvants, chemical additives or fertilizers unless recommended on the Varro® herbicide label. When tank mixing additive/adjuvant with Varro® herbicide, minor crop injury may be observed. These symptoms are temporary and do not impact crop yield.

Velocity m3 herbicide For more consistent control of wild oat in areas of heavy infestation, more consistent control of Japanese brome, control of ALS-resistant cleavers at the 4- to 6-whorl growth stage, control of Canada fleabane up to 10cm in height/diameter, suppression of giant ragweed at the 1 to 6-leaf stage and spreading atriplex at the 1 to 10-leaf stage add AMS.

AMS Rate:
99% solution: 500g/ha.
49% solution AMS: 1L/ha.
40% solution: 1.25L/ha.

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.

Tank mixtures: The applicable labeling for each product must be in the possession of the user at the time of application. Follow applicable use instructions, including application rates, precautions and restrictions of each product used in the tank mixture. Bayer has not tested all tank mix product formulations for compatibility or performance other than specifically listed by brand name. Always predetermine the compatibility of tank mixtures by mixing small proportional quantities in advance. Bayer, Bayer Cross, Buctril®, Converge®, Infinity®, Luxxur®, Olympus®, Option®, Pardner®, Puma®, R/T 540®, Roundup Transorb®, Roundup WeatherMAX®, Roundup Xtend®, Sencor®, Thumper®, Tundra®, VaporGrip®, Varro®, Vios® and XtendiMax® are registered trademarks of Bayer Group. Used under license. Velocity is a trademark of Bayer Group or its licensor. Used Under license. Liberty® is a registered trademark of BASF. All other trademarks are the property of their respective owners. Bayer CropScience Inc. is a member of CropLife Canada. ©2021 Bayer Group. All rights reserved. 1034_S3_CA