Pesticide Formulations: 5 Critical Mistakes in Mixing and Application That Reduce Effectiveness

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Pesticide formulations are designed to provide maximum efficacy in crop protection, but even minor errors in their preparation or application can lead to a significant reduction in performance. Incorrect mixing, failure to observe recommended ratios, or unsuitable application conditions can cause active ingredients to fail to penetrate the target organism or even degrade before they begin to act. In this article, we focus on five common mistakes that can affect the results of your work and provide advice on how to effectively prevent them.

1. Incorrect dilution of concentrates: Why precision determines efficacy

Pesticide formulations are designed to achieve optimal efficacy at a precisely defined concentration. One of the most common mistakes is failing to adhere to the recommended dilution, whether due to negligence or an attempt to save costs. Too low a concentration of the active ingredient leads to insufficient control of pests, weeds, or pathogens, while too high a concentration can cause phytotoxicity—damage to the treated crops. For example, with systemic herbicides, an excessive dose may slow growth or induce leaf deformations, which paradoxically reduces yield.

When diluting, it is crucial to use calibrated measuring containers and follow the manufacturer’s instructions. Water used as a diluent should have a neutral pH (ideally 6–7) and a low salt content, as these can affect the stability of the emulsion or dispersion. For EC-type formulations (emulsifiable concentrates), it is important to add the concentrate to the water while stirring continuously, rather than the other way around, to avoid the formation of insoluble clumps. Always check the homogeneity of the mixture—if separation or cloudiness occurs, the mixture should be remixed or prepared anew.

2. Ignoring Adjuvant Compatibility: When Additives Do More Harm Than Good

Adjuvants, such as wetting agents, penetrants, or adhesives, can significantly enhance the efficacy of pesticides by improving leaf coverage, accelerating absorption, or reducing evaporation. However, incorrect combinations with the main active ingredient may lead to chemical reactions that reduce the stability of the mixture or even inactivate the active substance. For example, anionic surfactants can react with cationic herbicides (e.g., paraquat) to form insoluble complexes, completely eliminating their effectiveness.

Always verify the compatibility of adjuvants with the pesticide before mixing, according to technical data sheets or consult your supplier. A compatibility test can be performed simply: mix a small amount of pesticide and adjuvant in a test tube with water and observe whether separation, cloudiness, or precipitate formation occurs. If so, the combination is not suitable. Also, pay attention to the order of adding components – adjuvants are usually added after diluting the pesticide to minimize the risk of undesirable reactions.

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3. Improper storage conditions: How temperature and humidity damage formulations

Pesticide formulations are sensitive to extreme temperatures, humidity, and light, which can accelerate the degradation of active ingredients. For example, emulsifiable concentrates (EC) crystallize at temperatures below 0 °C, leading to irreversible damage. Conversely, high temperatures (above 30 °C) can cause solvent evaporation or decomposition of sensitive components, such as pyrethroids. Humidity, on the other hand, threatens powder formulations (WP), which may clump or lose their dispersibility.

Store pesticides in a dry, well-ventilated area with temperatures between 5–25 °C, away from direct sunlight and heat sources. Original packaging should remain intact to prevent contamination or evaporation. For liquid formulations, regularly check for separation or color changes—this may indicate degradation. If pesticides must be stored under unsuitable conditions (e.g., in the field), use insulated containers and limit storage time to a minimum.

4. Poor Application Technique: Why Even a Correctly Mixed Pesticide Fails

The effectiveness of a pesticide depends not only on the correct formulation but also on the application technique. A common mistake is using the wrong type of nozzle, which does not provide the optimal droplet size. Droplets that are too large bounce off leaves or run off onto the ground, while droplets that are too small are carried away by the wind and do not reach the target. For example, with contact herbicides, even coverage of the leaf surface is key, whereas systemic pesticides require fewer droplets but with a longer retention time on the surface.

Before application, calibrate the sprayer according to the manufacturer's recommendations and select a nozzle suitable for the formulation type and target organism. For water-dilutable formulations (e.g., SC, SL), use nozzles with fine to medium dispersion, while for suspensions (WG), coarser dispersion nozzles are more appropriate to prevent clogging. Additionally, ensure the correct pressure and speed of movement—excessively high pressure increases evaporation and losses, whereas low pressure leads to uneven coverage. Apply in calm or light wind conditions (up to 3 m/s) and avoid extreme temperatures (above 25 °C), which increase evaporation.

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5. Neglecting water pH and its impact on the stability of active substances

Water used for diluting pesticide formulations is never chemically neutral – its pH ranges from acidic to alkaline and significantly affects the stability and efficacy of active ingredients. Many active substances, particularly from the organophosphate group or certain sulfonylurea-based herbicides, rapidly hydrolyze in alkaline conditions. This leads to their degradation before application, reducing the product's efficacy by up to 30–50%. Conversely, overly acidic pH can cause precipitation of some substances or increase their toxicity to non-target organisms.

Before each mixing, it is therefore essential to measure the water's pH using simple test strips or a digital pH meter. The ideal range for most pesticide formulations is between 5.5 and 7.0. If the pH is outside this range, it can be adjusted by adding acidic (e.g., citric acid) or alkaline (e.g., sodium bicarbonate) buffers. These substances are commonly available as specialized adjuvants, and their dosage must be carefully followed according to the manufacturer's recommendations to avoid undesirable interactions with the active ingredient.

6. Inadequate Mixing and Sedimentation: How to Prevent Uneven Distribution of the Active Ingredient

Pesticide formulations, especially suspension concentrates (SC) or emulsifiable concentrates (EC), tend to separate during storage or after dilution with water. Heavier particles settle at the bottom of the container, while lighter components remain on the surface. If the mixture is not thoroughly mixed before application, the active ingredient is unevenly distributed in the application equipment. As a result, some areas of the treated crop receive an underdose, while others receive an excessive concentration, which can lead to phytotoxicity or insufficient efficacy.

For proper mixing, it is crucial to follow several principles: Before opening the container with the concentrate, it should be thoroughly shaken to release any sediments. After adding it to water, the mixture must be vigorously stirred for at least 2–3 minutes, ideally using a mechanical mixer or circulation in the application equipment. For larger tanks, it is advisable to continuously stir the mixture during application to prevent re-sedimentation. For suspensions, it is also important to monitor viscosity – overly thick mixtures should be diluted with water to the recommended consistency; otherwise, there is a risk of nozzle clogging.

7. Exceeding the storage time of diluted mixtures: Why freshness determines the result

Many pesticide users underestimate the fact that diluted mixtures have limited stability, and storing them for longer than 24–48 hours can significantly reduce their effectiveness. Once the concentrate is diluted with water, chemical and physical processes begin that lead to the degradation of active substances. For example, some glyphosate-based herbicides lose their effectiveness after just 12 hours if stored in metal containers, where catalytic decomposition occurs. Similarly, copper-containing fungicides may form insoluble complexes in diluted form, which settle at the bottom of the container.

Diluted mixtures should always be prepared just before application and in quantities that can be used within one working day. If it is necessary to store the mixture longer, several precautions should be followed: Use containers made of inert materials (e.g., plastic canisters certified for chemicals), store at a temperature of 10–25 °C, and protect from direct sunlight. It is also important to regularly check the mixture for the presence of sediments or color changes, which indicate degradation. In case of doubt, it is always better to prepare a new mixture rather than risk ineffective application.

Do you need a consultation on your agrochemical raw materials?

Every pesticide formulation requires a specific approach – from storage to application. GCG Group provides detailed safety and technical data sheets for every raw material supplied, and our experts are happy to advise you on the selection and optimization of processes for your specific needs. Contact us – or browse our catalog of over 1,300 products right away.