Understanding adjuvants and surfactants for improved pest management in ornamental crop production – Part I
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EmailUnderstanding what adjuvants are and when to use them can improve pest management in ornamental crop production.
Pesticides are substances, either man-made or naturally occurring, that growers use to protect their crops. Their job is to manage pests like insects, weeds, fungi or even rodents that can harm plants. There are different types of pesticides depending on what they target, like insecticides for bugs, herbicides for weeds (Photo 1), and fungicides for fungi. They are categorized based on formulation and toxicity and play a vital role in protecting crops. However, adding adjuvants to pesticide mixtures may improve their performance. Understanding how adjuvants, especially surfactants, work can help growers make more effective, safer and economical pesticide applications.
In this article series, we will discuss details about adjuvants and surfactants, how they are different from each other, their application timings and types.
What are adjuvants?
According to Tu, M., & Randall, J. M. (2003) “Weed control methods handbook the nature conservancy,” adjuvants are chemical substances added to pesticide formulations or spray tanks to improve how the pesticide works. They do not have any direct pest control activity themselves, but they can:
- Improve the effectiveness of the pesticide
- Make it easier to mix with other products
- Change the way the spray behaves on plants
- Increase safety or reduce unintended effects
In other words, adjuvants help tailor pesticide applications to meet specific field needs, improve performance or adapt to local conditions.
When are adjuvants used?
Most pesticides already contain the necessary adjuvants included by the manufacturer. However, in certain situations, such as when dealing with tough environmental conditions, stubborn pests or tank-mixing different products, applicators may need to add extra adjuvants to the spray mixture.
It’s important to note that adjuvants are not regulated by the U.S. Environmental Protection Agency because they generally lack pesticidal properties. However, some states such as California define adjuvants as pesticides and require their use to be reported, but this is not the case nationwide. Thus, regulation and monitoring of adjuvants are inconsistent across the U.S.
Types of adjuvants according to the Core Manual of National Pesticide Application Certification
There are many types of adjuvants available, each designed for a specific purpose. Choosing the right one depends on your crop, pesticide, water quality and environmental conditions. The following is a quick guide to understand the most common types of adjuvants used in agriculture.
Defoamers. Defoamers help reduce excessive foam that can form during spray mixing, especially when using certain surfactants or when vigorous agitation is required. Some pesticide formulations, such as wettable powders or dry flowable, often need strong agitation to keep the mixture uniform. In these cases, adding a defoamer can prevent foaming and improve handling.
Compatibility agents. When tank-mixing multiple pesticides or combining pesticides with fertilizers, compatibility agents help prevent clumping, separation or other issues that can make the mixture unusable. They improve uniform mixing and reduce the risk of equipment blockage.
Drift control agents. These adjuvants help reduce spray drift by increasing droplet size or reducing the number of fine, lightweight droplets that can easily blow away. Drift control is especially important when applying pesticides near sensitive areas, water bodies or neighboring fields.
Buffers or pH modifiers. The effectiveness of many pesticides depends on the pH of the spray solution. Most pesticide mixtures are most stable when the water pH is between 5.5 and 7 according to the “Core Manual of National Pesticide Applicator Certification,” which is slightly acidic to neutral. Water that is too acidic or too alkaline can cause pesticides to break down quickly, reducing their effectiveness. Using a buffer or pH modifier helps maintain the ideal pH range. It’s important to first add the buffer to the spray tank water, mix thoroughly, and ensure the pH is correct before adding any pesticide or other adjuvants.
Extenders and stickers. Extenders help pesticides stay active on the target surface for a longer period, enhancing their effectiveness. Stickers improve how well pesticides adhere to plant surfaces, reducing the amount washed off by rain or irrigation. Some stickers also slow down evaporation and photo-degradation, giving the pesticide more time to work.
Wetting agents. Wetting agents help dry pesticide powders dissolve more easily in water, improving spray mixture uniformity and application consistency.
Spreader adjuvants. Spreaders help the spray solution form an even coating over the treated surface. A uniform layer ensures better pesticide coverage and improves effectiveness.
Safeners. Safeners reduce the risk of crop injury or toxicity from pesticides. They can also lower the hazard for the pesticide applicator by reducing harmful exposure during mixing and application.
Emulsifiers. Emulsifiers allow water-based pesticides to mix properly with petroleum-based carriers, ensuring a uniform spray solution. Without them, oil and water-based components may separate, reducing effectiveness.
Penetrants. Penetrants help pesticides move through the plant’s outer surface and into the inner tissues. This can be especially useful when applying systemic pesticides, which need to be absorbed into the plant to control pests. However, penetrants may not work equally well on all plant species.
Thickeners. Thickeners increase the viscosity (thickness) of the spray mixture. This can reduce spray drift and slow down evaporation. Thickeners are particularly helpful when applying systemic pesticides, as they extend the time available for absorption into plant leaves.
If unsure about which adjuvant to use, always:
- Read the pesticide product label, technical data sheets, safety data sheets or contact the product manufacturer for guidance.
- Follow any specific recommendations or restrictions mentioned on the label. The label is the law and will indicate which type to use, and what rate to apply. Never substitute one type of adjuvant for another without label approval.
- Many end-use products already contain adjuvants. Adding extra adjuvants without need can reduce effectiveness or cause unintended effects.
- Only use adjuvants specifically manufactured for agricultural or horticultural use. Avoid industrial or household products.
- Always follow good application practices, such as careful planning, accurate application, and post-application monitoring to ensure effectiveness and mitigate any danger. Test spray mixtures with adjuvants on a small area before applying across the entire field to avoid unexpected damage.
- Using the wrong adjuvant, or adding too much, can reduce pesticide effectiveness or cause unintended side effects.
