Agrochemical Adjuvants: How They Influence Pesticide Efficacy and What You Need to Know

Photo: Arjun MJ / Unsplash

Pesticides are the foundation of modern crop protection, but their effectiveness often depends on auxiliary substances—agrochemical adjuvants. These components improve wetting, penetration, or stability of the spray liquid, enabling a reduction in the dosage of active ingredients while maintaining the same efficacy. However, in practice, we frequently encounter mistakes in their selection or combination, which lead to lower efficiency, waste, or even crop damage. What types of adjuvants exist, how do they work, and what should you watch out for when using them?

What Are Agrochemical Adjuvants and Why Are They Used?

Agrochemical adjuvants are special substances added to pesticide formulations or application mixtures to improve their efficacy, stability, or application properties. Unlike the active ingredients in pesticides themselves, they do not have a pesticidal effect on their own but optimize the way the pesticide acts on the target organism. Their primary role is to compensate for the shortcomings of the pesticide itself, such as poor wetting, low penetration into plant tissues, or instability in aqueous environments. Typical examples include surfactants, oils, humectants, adhesives, or foaming agents, which are combined according to the specific needs of the application.

The use of adjuvants offers several key benefits. They increase the coverage and retention of the spray liquid on leaves, which is crucial especially for waxy or hairy surfaces where droplets would otherwise run off or bounce off. They also improve the penetration of active ingredients into plants, thereby enhancing their systemic effect. Adjuvants can also stabilize emulsions or suspensions, prevent evaporation, or improve spray distribution under unfavorable weather conditions. A properly selected adjuvant can thus reduce the required amount of pesticide by 20–30%, bringing both economic and ecological benefits.

How to choose the right adjuvant for a specific application?

The selection of a suitable adjuvant depends on several factors, including the type of pesticide, target crop, application conditions, and desired effect. The basic criterion is compatibility with the active ingredient—some adjuvants, for example, may cause phytotoxicity in sensitive crops or reduce emulsion stability. For herbicides, oil-based adjuvants are often used to enhance penetration through the waxy cuticle of weeds, while for fungicides and insecticides, surfactants that improve wetting and distribution on leaves are preferred.

Another important parameter is the surface tension of the spray liquid. Standard water has a surface tension of around 72 mN/m, which is too high for effective wetting of plant surfaces. Surfactant-based adjuvants reduce this tension to 30–40 mN/m, thereby enabling better droplet spread. For crops with dense pubescence or a waxy coating (e.g., cereals, brassicas), adjuvants with a higher oil or silicone surfactant content are recommended to ensure better adhesion. It is always advisable to conduct a preliminary compatibility and efficacy test on a small area.

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How do adjuvants affect safety and legislative requirements?

Although adjuvants are not active ingredients in pesticides, they are subject to strict legislative requirements, particularly the REACH and CLP/GHS regulations. Manufacturers and distributors must ensure that adjuvants meet the requirements for registration, classification, and labelling of hazardous substances. This includes assessing toxicity, ecotoxicity, and bioaccumulation potential. Some adjuvants, particularly those based on organic solvents or strong surfactants, may be classified as irritants or harmful to health, which requires appropriate protective measures during handling.

When combining adjuvants with pesticides, it is necessary to verify that no undesirable interactions occur that could increase the risk of phytotoxicity or reduce efficacy. For example, some oil-based adjuvants may enhance the penetration of pesticides into plants, which may be desirable for herbicides but undesirable for sensitive crops. It is also important to follow the recommended dosage, as excessive amounts of adjuvant can lead to crop damage or soil contamination. Always follow the manufacturer's instructions and applicable regulations for the safe use of chemicals in agriculture.

Practical tips for working with adjuvants in field conditions

When applying adjuvants in the field, it is crucial to follow several basic rules to ensure their maximum effectiveness and minimise risks. Before application, it is advisable to perform a small-scale compatibility test of the mixture, especially when combining multiple products. The spray liquid should be prepared immediately before use to avoid degradation or separation of components. The water temperature for preparing the mixture should be between 10–25 °C, as water that is too cold or too hot can affect the solubility and stability of adjuvants.

During application, it is important to ensure even coverage of the target area and adjust the pressure and nozzle size according to the adjuvant type. For example, silicone surfactants require lower pressure and finer droplets for optimal spreading, while oil-based adjuvants can be applied with coarser droplets. After application, it is necessary to thoroughly clean the application equipment to prevent cross-contamination or nozzle clogging. Last but not least, weather conditions should be monitored—adjuvants are most effective at temperatures of 15–25 °C and without strong wind, which could cause spray drift.

Photo: Dibakar Roy / Unsplash

How Adjuvants Improve Pesticide Penetration and Retention on Leaves

The effectiveness of pesticides depends not only on the active ingredient but also on how well the product adheres to the plant surface and penetrates its tissue. Adjuvants play a key role in optimizing these processes. Surfactants reduce the surface tension of spray droplets, thereby improving leaf wetting—especially on waxy or hairy surfaces where droplets would otherwise run off. For example, in cereals or brassica crops, adding a suitable surfactant can increase spray retention by 30–50%, which directly correlates with higher efficacy of herbicides or fungicides.

For the penetration of active substances into plant tissues, oil-type adjuvants (e.g., mineral or methylated vegetable oils) or penetrants are essential. These substances disrupt the cuticular waxes on leaves and facilitate the entry of pesticides into cells. In practice, this means that when applying systemic products (e.g., glyphosate), an adjuvant can reduce the required dose of the active ingredient by 10–20% without losing efficacy. However, it is important to adhere to recommended concentrations—excessively high doses of oil-based adjuvants can cause phytotoxicity, particularly in sensitive crops such as rapeseed or sunflower.

The Impact of Adjuvants on Spray Resistance to Weather Conditions

One of the common challenges in field conditions is the wash-off of spray by rain shortly after application. Adhesive or film-forming adjuvants can significantly increase the resistance of the product to precipitation. These substances form a protective film on the leaf surface, preventing the wash-off of the active ingredient even in rain within 1–2 hours after application. For example, with contact fungicides (e.g., against potato blight), the use of an adhesive adjuvant can reduce efficacy losses by up to 40% in the event of rain within 6 hours after spraying.

Another factor is the evaporation of water from the spray liquid, which can lead to crystallization of the active substance on the leaf surface and reduce its availability. Adjuvants with retention properties (e.g., humectants) bind moisture and extend the period during which the product remains in its active form. This is particularly important during applications at high temperatures (above 25 °C) or low air humidity. However, when using these adjuvants, it is necessary to ensure compatibility with other components of the mixture—some humectants may interact with ionic surfactants and cause flocculation or reduced efficacy.

How Adjuvants Affect Spray Distribution and Drift Minimization

Uniform spray distribution and drift minimization are key to effective and environmentally friendly pesticide application. Adjuvants such as adhesives or viscosity modifiers can improve droplet size spectrum and reduce the proportion of fine droplets (below 100 μm), which are most prone to drift. For example, adding a polymer-based adjuvant can increase the proportion of medium-sized droplets (200–400 μm) by up to 30%, leading to better coverage of the target area and reduced risk of contamination of surrounding crops or water sources.

For applications in windy conditions, adjuvants with high density or viscosity are suitable, as they stabilize droplets and prevent their dispersion. However, these substances may increase pressure in the spraying system, so it is necessary to adjust nozzle settings and working pressure accordingly. In practice, it is recommended to test the compatibility of the adjuvant with the specific spraying equipment before large-scale application. It is also important to follow the recommended dosage—excessive concentration of a viscous adjuvant can lead to nozzle clogging and uneven coverage.

Need advice on selecting adjuvants?

Every agrochemical formulation requires an individual approach. GCG Group provides detailed technical and safety data sheets for all supplied raw materials and advises on selecting the optimal adjuvants for your specific application. Contact us – or browse our catalogue of over 1,300 products.