Agricultural Adjuvants – A Formulator’s Perspective

Agricultural adjuvants are materials used to enhance the activity and efficacy of pesticide sprays such as herbicides, insecticides and fungicides to control or eliminate unwanted pests. Agricultural adjuvants do not function as active substances like pesticides, instead they reinforce or amplify their pesticidal effect.  
 

Adjuvants can be classified into two major categories: activator and utility adjuvants, the former class dominates over the latter in terms of market share. Activator adjuvants generally modify properties of the spray mixture to help the pesticide penetrate or protect the target organism. The most typical activator adjuvants are surfactants (a major leader), emulsifiers, oils and ammonium salts (fertilizers). Utility adjuvants include water conditioners, drift control, compatibility agents, acidifier/buffers and antifoams. Functionally speaking, each of these adjuvants modifies physical properties of the liquid sprays. 
 

Utility adjuvants may affect spreading, penetration, droplet size and other characteristics critical to the performance of the pesticide spray mixture. Among the pesticide markets, adjuvants for the herbicide segment have the most growth opportunities.
 

Major players
 

Worldwide there are scores of agro-adjuvant manufacturers and suppliers. The leading companies engaged in innovations include:  Adjuvant Plus Inc. (Canada), Akzonoble N.V. (Netherlands), Brandt Consolidated (U.S.), Clariant International Ltd. (Switzerland), Lamberti SpA (Italy), Momentive Performance Materials (U.S), Solvay SA (Belgium), Dow Corning (U.S.), Croda Chemicals (India), Tanatex Chemicals BV (Netherlands), Helena Chemical Company (U.S.), and others. Their adjuvant products and services cover both activator and utility categories.  

 

Adjuvants and pesticide performance
 

Adjuvants as part of the pesticide application package can be included as an in-can (built-in) component by the formulator or added separately when a spray mixture is prepared by the applicator in the field. The latter case is the so-called tank mixing adjuvant.  In-can adjuvants can be rather effective and perform well under control, however space limitations occasionally require some needed adjuvants to be added separately through tank mixing to boost the field performance of the pesticide formulation.

Unique characteristics of adjuvants involve the complex mechanism associated with the pesticide spray. Using herbicide adjuvants as an example, there will typically be interactions between the leaf surface structure, spray droplet size, and the adjuvant molecules when the herbicide is applied to the plant. 

 

Despite the fact that many scientific investigations have been carried out over decades to understand the interplay of the spray system of interest, no simple mechanism has been uncovered. It is quite pesticide and crop plant specific. 

 

One noted example is the interaction between glyphosate herbicide and adjuvant surfactants. In most cases, common surfactant adjuvants added to glyphosate spray solution dropped the surface tension and droplet contact angles. As a result, spray deposition, spray retention and leaf wetting increased, leading directly to increased herbicide uptake and enhanced glyphosate activity. 

 

There are other cases where adjuvant effects on glyphosate treatments were more species specific. Increased spray delivery does not always translate to increased control of certain weeds. Possible reasons for the decreased effectiveness from glyphosate treatments in the field involve the hydrophobic cuticle waxes, poor droplet spreading, longer drying time and antagonism among certain adjuvants. As a result it is essential for applicators to follow strict instructions on the formulation label so adjuvants are not misused or mismatched with the prospective herbicide. 

 

 

Restrictions in how adjuvants are used vary between countries. In Europe, adjuvants for tank mixing use is regulated under legislative control (REACH), article 58 (2), though there is derogation for member states until the program is fully implemented. In Canada, the Pest Management Regulatory Agency (PMRA) regulates adjuvants. Agricultural tank adjuvants are largely unregulated in the United States, except for a few isolated cases. 

 

Obviously, in-can adjuvants in any pesticide’s co-formulation is regulated as usual, but groups within the private adjuvants industry, such as the American Society for Testing and Materials International (ASTM) and Council of Producers & Distributors of Agrotechnology (CPDA), have made efforts to self-regulate adjuvant products in the US. All these efforts are an attempt to standardize or voluntarily certify adjuvants in the mix tank.

 

 

The current trend in adjuvant technology development is to move alongside agrochemicals as world population continues to grow and demand for food and fiber supplies increases. The outlook for adjuvant development is quite bright as adjuvant manufacturers strive for new products to help their agrochemical and farm customers. The industrial trend is moving toward new adjuvant molecules and formulations with multi-components and multi-functionality in a single package, if possible, while trying to utilize green chemistry which is eco-friendly and safer to the personnel involved. Two noted examples are Synergen® OS under the EcoTain® platform from Clariant, and Atplus™ UCL 1007 from Croda.  Synergen OS features a methylated seed oil with a tailored polyglycerol ester as an effective herbicide penetrant. Atplus UCL 1007 features a surfactant-urea complex pair working as a dry tank-mix adjuvant with excellent water solubility.