Milan Brankov1*
Milena Simić1
Jelena Vukadinović1
Miloš Zarić2
Alexandros Tataridas3
Sofija Božinović1
Vesna Dragičević1- 1Research Department, Maize Research Institute “Zemun Polje”, Belgrade, Serbia
- 2West Central Research, Extension and Education Center, University of Nebraska-Lincoln, North Platte, NE, United States
- 3Centre for Functional Ecology (CFE), University of Coimbra, Coimbra, Portugal
Adjuvants are agrochemicals or natural substances, commonly mixed with pesticides to increase their efficacy or reduce off-target movement by modifying the physical properties of the spray solution, such as surface tension, droplet size, and spreadability, which ultimately improve pesticide adhesion and coverage on target surfaces. Adjuvant use across Europe remains less widespread compared to regions like the USA, where adjuvants are often recommended or required with certain herbicide applications. This paper highlights the potential benefits of incorporating adjuvants with herbicides in weed control, particularly as a strategy to reduce overall herbicide use. Findings from dose-response research on available adjuvants suggest they may enable the application of lower herbicide rates than typically recommended, without sacrificing effectiveness, thereby contributing to the goal of reducing herbicide use by 50% by 2030 in Europe. Furthermore, literature findings indicate that adjuvants significantly improve weed control by enhancing the performance of active ingredients, with efficacy increases of up to 50% compared to using herbicides alone. The integration of adjuvants into herbicide tank mixtures offers considerable promise, especially for managing herbicide-resistant weeds and achieving effective weed control.
1 Introduction
The viability and future of agriculture is threatened globally by climate change and pressing factors such as the spread of invasive weeds and the expansion of herbicide resistance weeds. Crop yields are more prone to decline, and crop production is more challenging than ever, especially on degraded soils and among smallholder farmers. For decades farmers, in particular in Global North, have depended heavily on synthetic herbicides and chemical inputs to “feed” a production model that is no longer attractive or even profitable, that of industrial agriculture. Furthermore, a lack of new herbicide active ingredients on the market along with the rapid spreading of herbicide resistant weeds recently, made imperative the pursuit of new solutions to reduce the dependency on chemical weed control and strategies that work with nature, and not against it, to reduce the weed pressure. In Europe, the European Commission has required the reduction of the use of pesticides (including herbicides) by 50% by 2030 (Tataridas et al., 2022), in order to reduce the negative impacts of their use on soil health, biodiversity, and human health. Currently, there is a growing movement in Europe towards more sustainable and environmentally friendly farming practices to alleviate the effects of decades of harmful practices such as excessive use of pesticides, extensive soil disturbance and monocropping. Although very challenging, there are several options on how to reduce the herbicide load. This perspective article will not list already existing and well-documented strategies and practices that lead to herbicide reduction and eventually elimination (e.g., cover crops, mechanical means, biological agents, crop diversification, new technologies etc.). Instead, it will explore and highlight the role of adjuvants in herbicide reduction as a tool to assist the transition of conventional farming systems towards agroecology (Figure 1). Adding adjuvants into the tank and mixing them with herbicides can help in obtaining higher efficacy on the weeds, even when herbicides are applied in reduced rates or in unsuitable conditions.
Figure 1. The significance of adjuvants in agroecological weed management.
The potential to use lower herbicide rates with the help of adjuvants was recognized two decades ago. Adjuvants are agrochemicals or natural substances commonly used to improve pesticide efficacy and reduce particle drift by altering the physical properties of the spray solution. Adjuvants can be classified based on their composition and functional properties as surfactants, oils, solvents, polymers, salts, diluents, humectants, and water conditioners (Hazen, 2000). Some of them, like surfactants, can increase the spreading and wetting area of droplets on the leaves of plants (Buffington and McDonald, 2006). Likewise, some adjuvants increase herbicide penetration and adsorption through cuticles and improve the homogeneity of spray coverage, particularly on waxy and leaf surfaces with trichomes (Xu et al., 2010). Oils, especially methylated seed oils are adjuvants as well, mixed with an emulsifier to allow for dispersion in water (Bunting et al., 2004). Furthermore, polymers as adjuvants enhance droplets spreading and change their evaporation dynamics (Katzman et al., 2023). Literature reports using lower herbicide rates together with adjuvants, where results did not differ from the same treatments containing the same herbicide at full rate without adjuvants (Brankov et al., 2023b).
As herbicides are registered for application at specific recommended rates, any deviation causes much discussion, especially among scientists. The reason for this might be found that exposure to sub-lethal doses of herbicide may directly lead to resistance evolution in weeds (Gressel, 2011). As documented earlier, in drift simulation studies, several weeds may develop lower susceptibility to some herbicides (Vieira et al., 2020). If weeds are exposed to those doses and survive, they will likely establish target site insensitivity. Management of those weeds might be even more complicated as they can resist wider spectra of herbicide groups (Vieira et al., 2020).
This paper sought to highlight the effects of mixing herbicides with adjuvants on weed control and to emphasize adjuvants as an often-underestimated tool for increasing herbicide efficacy and ultimately reducing the need for unnecessary sprayings.
2 Adjuvants: concept and characterization
As written in the latest Shaner (2014) published by the Weed Science Society of America (WSSA), there is a need to assign common names for adjuvants to reduce confusion when they are mentioned. The nomenclature task is difficult, as many existing adjuvants are mixtures of different constituents. To date, WSSA uses the chemical names of adjuvants used by EPA (Environmental Protection Agency) or FDA (Food and Drug Administration). Adjuvant recommendations are specific for each herbicide product, based on research and developed by the herbicide manufacturers, trying to address different regional and/or environmental needs. Some herbicides are generally formulated with sufficient adjuvants and may not require additional adjuvants. However, other herbicides have specific adjuvant recommendations that must be added to the spraying mixture. Herbicide glyphosate is a good example. There are variabilities between glyphosate products in the type of glyphosate salt in the formulation, as well as in the additives added in the product, which can improve handling, safety and solubility of products (Leaper and Holloway, 2000).
Since adjuvants do not have any pesticide properties, they are not required to be registered by the EPA. A similar situation is across the EU, where adjuvants fall within the scope of Regulation (EC) No 1107/2009. No specific requirements (including data necessities, notification, evaluation, assessment, and decision-making procedures) for the authorization of adjuvants have been set at the EU level. Therefore, the potential of adjuvants to increase herbicide efficacy is high. Owing to the need to solve problems in weed control and increase herbicide efficacy, the manufacturing industry constantly develops various adjuvants and provides recommendations for their integration across various tank mixtures.
3 Positive effects of mixing adjuvants with herbicides in the tank
It is generally known that adjuvants could improve the efficacy of herbicide-active ingredients. As adjuvant changes in the physical properties of herbicide solutions, they might increase penetration and adsorption into the plant. Sobiech et al. (2020) (Sobiech et al., 2020) reported that added MSO (methylated seed oil) adjuvant could mitigate the adverse effects of the low pH of herbicide sulcotrione. Combining the adjuvant and reduced rate of sulcotrione affected barnyardgrass the same way as the full recommended rate of sulcotrione without the adjuvant. Moraes et al., 2021 (Moraes et al., 2021) showed that adjuvants have the potential to overcome the antagonistic interaction between herbicides, taking into account that it is dependent on the weed species. In their study, addition of a NIS (non-ionic surfactant) adjuvant to glyphosate plus lactofen tank-mixture increased common lambsquaters control. Pratt et al. (2003) (Pratt et al., 2003) reported that using tap water glyphosate solution containing 2% of AMS (ammonium-sulfate) adjuvant increased velvetleaf control (up to 53% compared to glyphosate solution alone). Idziak et al., 2023 (Idziak et al., 2023) indicated that high efficacy of herbicides could be achieved even by using reduced rates of herbicides while needed to add certain adjuvants into the tank. In their study, effective control of Echinocloa crus-galli was achieved using reduced rate of nicosulfuron, when adding MSO adjuvant. Using lower herbicide rates to obtain satisfactory weed control was also confirmed by Brankov et al. (2023b). In their study, they used ED50 values of tested herbicides while adding MSO and NIS adjuvants delivered 98 and 99% of biomass reduction in Echinochloa crus-galli, which is an increase in herbicide efficacy up to 38%. In another study, the use of various herbicides with the NIS adjuvants to control weedy sunflowers was significantly increased, especially when half of the recommended rates were used for glyphosate and nicosulfuron. In the study with nicosulfuron, Brankov et al. (2023a) reported that using NIS adjuvant in field conditions significantly increased efficacy, allowing the use of nozzle-producing coarse droplets. Significantly reduced surface tension and contact angle was achieved with three sulfonylurea herbicides by adding five bio-ionic liquids as adjuvants (Marcinkowska et al., 2018) (Table 1).
Table 1. Examples of positive effects of adding of adjuvants on herbicide efficacy.
4 Some antagonistic effects of mixing adjuvants and herbicides on weeds and crops
Adding adjuvants may not always increase herbicide efficacy; in some cases, it could reduce it. Literature reports suggest that certain adjuvants can reduce weed control efficacy when tank-mixed with herbicides. Brankov et al. (2024b) reported that using AMS with nicosulfuron led to 20-30% reduced efficacy on the Chenopodium album. Cases of adding AMS to glufosinate lead to reduced efficacy in Abutilon theophrasti, also reported by Maschhoff et al., 2000 (Maschhoff et al., 2000). Furthermore, in control Cyperus rotundus, adding NIS and COC (crop oil concentrate) surfactants to glufosinate ammonium reduced the efficacy, again (Devendra et al., 2004). Presented evidence showed that, in some cases, adding adjuvants into the tank can be problematic and even negatively influence weed control (Table 2).
Table 2. Examples of negative (antagonistic) effects of addingof adjuvants on herbicide efficacy.
5 Negative effects of adjuvants on crops
In cases when adjuvants decrease weed efficacy, consequence are present in yield loss. However, in some cases adding adjuvants directly influence crops, making injuries due to increased herbicide intake by the crop. Listed are some evidences. Evaluating bentazone efficacy adding adjuvants on green pea, adding the adjuvant NIS (Sylgard 309) adjuvant combined with bentazone resulted in highest injury on green pea (Al-Khatib et al., 1995). Richardson et al., 2014 (Richardson et al., 2004) reported injuries on cotton following applications with CGA 362622 adding the COC adjuvant. In soybeans, adding NIS or COC adjuvant induced injuries with AC 263222 in post applications (Wixson and Shaw, 1991). In potatoes, mixing metribuzin and rimsulfuron caused higher injuries when adding MSO or COC, while lower injuries occurred when mixing it with NIS adjuvant (Hutchinson et al., 2004) (Table 3).
Table 3. Examples of negative effects of adding of adjuvants on herbicide selectivity.
6 Conclusions
The fundamental advantage of using adjuvants is reflected in the possible reduced use rates of herbicides. This short review highlights various effects of adding adjuvants into the tank with herbicides. In many cases, adding adjuvants increased herbicide efficacy compared to the sole active ingredient, even with lower herbicide rates than recommended. Combinations of weed management practices (e.g., cover crops, grazing, mechanical means etc.) are needed to ensure that herbicides with adjuvants remain the last option to manage noxious weeds and secure a sufficient yield. Thus, adjuvants could be an agroecological tool to reduce herbicide usage while not sacrificing overall product performance. Having increased efficacy directly means increasing crop yields and, presumably, profit. However, caution is required when using lower rates than labeled, as it could directly lead to herbicide resistance occurrence in weeds. Up to now, adjuvant use across the EU is less widespread than in the US. Therefore, increasing their status as environmentally friendly agrochemicals throughout Europe’s agroecological regions would be crucial as one of several tools in reducing rates of herbicides. Consequently, more European research is required to integrate various controlled or in-field conditions with different herbicide rates and a more comprehensive range of crops and weeds to confirm the broader insight, provide details, and give recommendations for adjuvant use across diverse environments. That information could be valuable for farmers (especially conventional ones) and advisors since combined use of herbicides in lower rates and adjuvants might theoretically result in a satisfactory weed control. This is in full agreement with the goals of Green Deal and agroecology approaches. Up to now, adjuvant use across the EU is not so popular like in the US.
Data availability statement
The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.
Author contributions
MB: Conceptualization, Writing – original draft, Writing – review & editing. MS: Conceptualization, Writing – original draft, Writing – review & editing. JV: Methodology, Supervision, Writing – original draft, Writing – review & editing. MZ: Supervision, Writing – original draft, Writing – review & editing. AT: Supervision, Writing – original draft, Writing – review & editing. SB: Validation, Writing – original draft, Writing – review & editing. VD: Conceptualization, Methodology, Supervision, Validation, Writing – original draft, Writing – review & editing.
Funding
The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Funded by the European Union under Grant Agreement No. 101083589. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or REA. Neither the European Union nor the granting authority can be held responsible for them.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declare that no Generative AI was used in the creation of this manuscript.
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References
Al-Khatib K., Kadir S., Libbey C. (1995). Effect of adjuvants on bentazon efficacy in green pea (Pisum sativum). Weed Technol. 9, 426–431. doi: 10.1017/S0890037X00023630
Brankov M., Simić M., Piskackova T., Zarić M., Rajković M., Pavlović N., et al. (2024a). A post-emergence herbicide program for weedy sunflower (Helianthus annuus L.) control in maize. Phytoparasitica 52, 12. doi: 10.1007/s12600-024-01126-w
Brankov M., Simić M., Samuelson S. L., Nikolić D., Čamdžija Z., Mandić V., et al. (2024b). Nicosulfuron weed control in maize as influenced by adjuvants: original vs. Generic herbicide. J. Crop Health 76, 1117–1124. doi: 10.1007/s10343-024-01014-7
Brankov M., Simić M., Ulber L., Tolimir M., Chachalis D., Dragičević V. (2023a). Effects of nozzle type and adjuvant selection on common lambsquarters (Chenopodium album) and johnsongrass (Sorghum halepense) control using nicosulfuron in corn. Weed Technol. 37, 156–164. doi: 10.1017/wet.2023.16
Brankov M., Vieira B. C., Alves G. S., Zaric M., Vukoja B., Houston T., et al. (2023b). Adjuvant and nozzle effects on weed control using mesotrione and rimsulfuron plus thifensulfuron-methyl. Crop Prot. 167, 106209. doi: 10.1016/j.cropro.2023.106209
Buffington E. J., McDonald S. K. (2006). 301 adjuvants & Surfactants 2. Available at: https://webdoc.agsci.colostate.edu/cepep/FactSheets/301Adjuvants&Surfactants.pdf.
Bunting J. A., Sprague C. L., Riechers D. E. (2004). Proper adjuvant selection for foramsulfuron activity. Crop Prot. 23, 361–366. doi: 10.1016/j.cropro.2003.08.022
Devendra R., Umamahesh V., Prasad T. V. R., Prasad T. G., Asha S. T. (2004). Influence of surfactants on efficacy of different herbicides in control of cyperus rotundus and oxalis latifolia. Curr. Sci. 86, 1148–1151.
Gressel J. (2011). Low pesticide rates may hasten the evolution of resistance by increasing mutation frequencies. Pest Manage. Sci. 67, 253–257. doi: 10.1002/ps.2071
Hazen J. L. (2000). Adjuvants—Terminology, classification, and chemistry. Weed Technol. 14, 773–784. doi: 10.1614/0890-037X(2000)014[0773:ATCAC]2.0.CO;2
Hutchinson P. J. S., Eberlein C. V., Tonks D. J. (2004). Broadleaf weed control and potato crop safety with postemergence rimsulfuron, metribuzin, and adjuvant combinations. Weed Technol. 18, 750–756. doi: 10.1614/WT-03-172R1
Idziak R., Sobczak A., Waligora H., Szulc P. (2023). Impact of multifunctional adjuvants on efficacy of sulfonylurea herbicide applied in maize (Zea mays L.). Plants 12, 1118. doi: 10.3390/plants12051118
Katzman D., Zivan O., Dubowski Y. (2023). Assessing the influence of polymer-based anti-drift adjuvants on the photolysis, volatilization, and secondary drift of pesticides after application. Atmosphere 14, 1627. doi: 10.3390/atmos14111627
Leaper C., Holloway P. J. (2000). Adjuvants and glyphosate activity. Pest Manage. Sci. 56, 313–319. doi: 10.1002/(SICI)1526-4998(200004)56:4<313::AID-PS147>3.0.CO;2-3
Marcinkowska K., Praczyk T., Łęgosz B., Biedziak A., Pernak J. (2018). Bio-ionic Liquids as Adjuvants for Sulfonylurea Herbicides. Weed Science. 66 (3), 404–14. doi: 10.1017/wsc.2017.85
Maschhoff J. R., Hart S. E., Baldwin J. L. (2000). Effect of ammonium sulfate on the efficacy, absorption, and translocation of glufosinate. Weed Sci. 48, 2–6. doi: 10.1614/0043-1745(2000)048[0002:EOASOT]2.0.CO;2
Moraes J. G., Butts T. R., M. Anunciato V., Luck J. D., Hoffmann W. C., Antuniassi U. R., et al. (2021). Nozzle selection and adjuvant impact on the efficacy of glyphosate and PPO-inhibiting herbicide tank-mixtures. Agronomy 11, 754. doi: 10.3390/agronomy11040754
Polli E. G., Alves G. S., de Oliveira J. V., Kruger G. R. (2021). Physical–chemical properties, droplet size, and efficacy of dicamba plus glyphosate tank mixture influenced by adjuvants. Agronomy 11, 1321. doi: 10.3390/agronomy11071321
Pratt D., Kells J. J., Penner D. (2003). Substitutes for ammonium sulfate as additives with glyphosate and glufosinate1. wete 17, 576–581. doi: 10.1614/0890-037X(2003)017[0576:SFASAA]2.0.CO;2
Richardson R. J., Wilson H. P., Armel G. R., Hines T. E. (2004). Influence of adjuvants on cotton (Gossypium hirsutum) response to postemergence applications of CGA 362622. Weed Technol. 18, 9–15. doi: 10.1614/WT-02-058
Sobiech Ł., Grzanka M., Skrzypczak G., Idziak R., Włodarczak S., Ochowiak M. (2020). Effect of adjuvants and pH adjuster on the efficacy of sulcotrione herbicide. Agronomy 10, 530. doi: 10.3390/agronomy10040530
Tataridas A., Kanatas P., Chatzigeorgiou A., Zannopoulos S., Travlos I. (2022). Sustainable crop and weed management in the era of the EU green deal: A survival guide. Agronomy 12, 589. doi: 10.3390/agronomy12030589
Vieira B. C., Luck J. D., Amundsen K. L., Werle R., Gaines T. A., Kruger G. R. (2020). Herbicide drift exposure leads to reduced herbicide sensitivity in amaranthus spp. Sci. Rep. 10, 2146. doi: 10.1038/s41598-020-59126-9
Wixson M. B., Shaw D. R. (1991). Effect of adjuvants on weed control and soybean (Glycine max) tolerance with AC 263,222. Weed Technol. 5, 817–822. doi: 10.1017/S0890037X00033911
Keywords: adjuvants, herbicides, tank mix, sustainable agriculture, agroecology
Citation: Brankov M, Simić M, Vukadinović J, Zarić M, Tataridas A, Božinović S and Dragičević V (2025) Could adjuvants serve as an agroecological tool? Front. Agron. 6:1523208. doi: 10.3389/fagro.2024.1523208
Received: 05 November 2024; Accepted: 09 December 2024;
Published: 14 January 2025.
Edited by:
Simerjeet Kaur, Punjab Agricultural University, IndiaReviewed by:
Miroslav Jursík, Czech University of Life Sciences Prague, CzechiaCopyright © 2025 Brankov, Simić, Vukadinović, Zarić, Tataridas, Božinović and Dragičević. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Milan Brankov, bWJyYW5rb3ZAbXJpenAucnM=