How Adjuvants Boost Pesticide Effectiveness

Photo: James Baltz / Unsplash

Manufacturers of pesticide formulations know well that the active ingredient alone is not enough. Even with precise dosing, low efficacy, waste, or crop damage can occur—often due to poor interaction with the target surface. Adjuvants, though frequently overlooked, play a key role in optimizing the physicochemical properties of sprays. From reducing surface tension to improving weather resistance, their proper selection can make the difference between average and top-tier performance. In this article, we focus on the specific mechanisms by which adjuvants work and provide practical tips on how to use them in production.

What are adjuvants and why are they key to pesticide efficacy

Adjuvants are auxiliary substances added to pesticide formulations or application mixtures to improve their physicochemical properties and thereby enhance the efficacy of active ingredients. Their role is to optimize processes such as wetting, penetration, adhesion, or resistance to rain wash-off. Typically, these are surfactants, oils, solvents, humectants, or adhesives that act synergistically with the active components of pesticides. Without adjuvants, many pesticides would not achieve the desired effect, especially under unfavorable conditions such as low humidity, high temperature, or the presence of waxy layers on the leaves of target plants.

In practice, adjuvants address specific problems commonly faced by pesticide manufacturers and farmers. For example, non-ionic surfactants reduce the surface tension of spray droplets, enabling more even coverage of the leaf surface and better penetration of the active ingredient. Mineral or vegetable oils, in turn, increase resistance to evaporation and improve the uptake of systemic pesticides. The correct selection and dosage of an adjuvant can reduce the required amount of active ingredient by 20–30%, bringing both economic and ecological benefits.

How to select the right adjuvant for a specific pesticide formulation

The selection of a suitable adjuvant depends on several factors, including the type of pesticide (herbicide, insecticide, fungicide), the target organism, application conditions, and the properties of the formulation itself. For example, for contact herbicides that act on the leaf surface, adjuvants that enhance adhesion and wetting, such as silicone surfactants, are ideal. Conversely, for systemic pesticides that must penetrate plant tissues, oil-based adjuvants or penetration agents that facilitate passage through cell membranes are more appropriate.

It is also important to consider the compatibility of the adjuvant with the active ingredient and other formulation components. Some adjuvants may cause phase separation, precipitation, or degradation of the active ingredient, leading to reduced efficacy or even damage to application equipment. Therefore, before final selection, it is essential to conduct laboratory stability tests of the mixture and verify its application properties, for example, through wetting tests on model surfaces or rainfastness tests according to standard methods.

Photo: James Baltz / Unsplash

Practical recommendations for adjuvant dosing and mixing

The dosage of adjuvants is guided by the manufacturer's instructions and the results of previous tests, but the general rule is that less is often more. Adding too high a concentration of adjuvant can lead to phytotoxicity, unnecessary waste of raw materials, or even antagonism with the active ingredient. Typical dosages range from 0.1–2% by volume in the spray mixture, with the exact value depending on the type of adjuvant and the target crop. For example, oil-based adjuvants are often recommended at a concentration of 0.5–1%, while silicone surfactants require only 0.05–0.2%.

When mixing adjuvants with pesticides, it is crucial to follow the correct order of adding components to the sprayer tank. Generally, it is recommended to first fill the tank halfway with water, then add the adjuvant and mix thoroughly. Next, add the pesticide and finally top up with water to the desired volume. This procedure minimizes the risk of sediment or foam formation. For some adjuvants, particularly oil-based ones, it is advisable to use a pre-mixed concentrate to ensure homogeneous distribution throughout the mixture.

How Adjuvants Contribute to the Sustainability and Economics of Pesticide Use

The use of adjuvants brings significant economic and ecological benefits. By increasing the efficacy of pesticides, they allow for a reduction in the total amount of active ingredients applied, leading to lower plant protection costs and reduced environmental impact. For example, evaporation-reducing adjuvants enable pesticide application even at higher temperatures, where rapid loss of the active ingredient would otherwise occur. This extends the application window and reduces the need for repeated spraying.

Another aspect is compatibility with integrated pest management principles and regulations such as REACH and CLP. Modern adjuvants are designed to minimize risks to non-target organisms and the environment. For example, biodegradable surfactants or plant oil-based adjuvants replace traditional synthetic substances with higher ecotoxicity. For pesticide manufacturers, this means the ability to offer formulations with a better ecological profile, which is a significant competitive advantage in the current sustainability trend.

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How adjuvants affect the physicochemical properties of spray liquids

Adjuvants play a key role in optimizing the physico-chemical properties of spray liquids, which directly affects the efficacy of pesticide application. The most important parameters include surface tension, viscosity, pH, and emulsion stability. For example, surfactants reduce the surface tension of water, enabling better wetting of the leaf surface and even distribution of droplets. This is particularly important for hydrophobic surfaces, such as the waxy leaves of certain crops, where without an adjuvant, the liquid would run off, leading to loss of the active ingredient.

Another critical factor is the viscosity of the mixture. Too low a viscosity leads to the formation of fine droplets, which are prone to wind drift, while high viscosity can cause nozzle clogging and uneven application. Adjuvants such as thickeners or rheology modifiers help achieve the optimal consistency. For systemic pesticides, the ability of the adjuvant to facilitate the penetration of the active ingredient through the plant cuticle is also important, which is ensured, for example, by penetration agents based on oils or esters.

Compatibility of Adjuvants with Different Types of Pesticide Formulations

The selection of an adjuvant must take into account the type of pesticide formulation to avoid undesirable interactions that could reduce efficacy or cause phytotoxicity. For soluble concentrates (SL), adjuvants based on non-ionic surfactants are often used to improve wetting and penetration. Conversely, for suspension concentrates (SC) or emulsifiable concentrates (EC), the stability of the suspension or emulsion is key, so adjuvants with dispersing or emulsifying properties are chosen.

Special attention is required for formulations containing sensitive active ingredients, such as certain sulfonylurea-based herbicides or growth regulators. Incorrectly selected adjuvants can cause chemical degradation of the active ingredient or increase the risk of crop damage in these products. For example, strongly alkaline adjuvants may accelerate the hydrolysis of some pesticides, while acidic adjuvants can destabilize emulsions. We always recommend conducting small-scale compatibility tests according to standard laboratory procedures before combining products.

How Adjuvants Address Specific Challenges in Field Conditions

In practice, adjuvants often determine the success of an application under challenging field conditions, such as high temperatures, low air humidity, or the presence of dust on leaves. For example, in dry areas, adjuvants with retention properties are effective, as they prevent rapid water evaporation from droplets and prolong contact time with the target surface. For applications in high temperatures, adjuvants with thermostable components are suitable, as they do not lose effectiveness even at temperatures above 30 °C.

Another challenge is the application on crops with dense foliage or on difficult-to-wet surfaces, such as the leaves of cereals or brassica crops. Here, adjuvants with adhesive properties are used, which increase droplet adhesion and prevent runoff. For systemic pesticides, it is also important that the adjuvant supports rapid penetration of the active ingredient into plant tissues, which is ensured, for example, by oil-based adjuvants with a high content of fatty acid esters. The selection of the adjuvant should always be tailored to the specific application conditions and the target crop.

Need advice on selecting raw materials?

Every agrochemical raw material requires an individual approach. GCG Group provides detailed technical and safety data sheets for each product, and our experts are happy to assist you in selecting suitable adjuvants or optimizing your formulation according to specific requirements. Contact us – or browse our catalog of over 1,300 products right away.