Pesticides formulations: An adjuvant
A pesticide formulation is a combination of active and inert ingredients that forms an end-use pesticide product. Pesticides are formulated to make them safer or easier to use. This is because many pesticide active ingredients, in “pure” (technical grade) form, are not suitable for application. In their concentrated form, some are extremely toxic, many do not mix well with water, some are unstable, and some are difficult (or unsafe) to handle, transport, or store. To address these problems, manufacturers add inert ingredients to end-use pesticide products. Inert ingredients have no pesticidal activity, and some simply serve as diluents or carriers.
An adjuvant is a chemical that can affect how a pesticide works.
- Improve the action of a pesticide.
- Change the characteristics of a pesticide formulation or a spray mixture (suspension or solution).
Most end-use pesticide products, especially those that are applied to foliage, contain adjuvants. However, in some situations, applicators may add them to a tank mix when making a finished spray mixture. Many adjuvants increase effectiveness and/or safety. Although they enhance the action of a pesticide or modify the properties of a spray solution, adjuvants alone have no pesticidal activity. Use them to customize the product or formulation for specific needs or to compensate for local conditions.
Because adjuvants lack pesticidal properties, the U.S. Environmental Protection Agency does not register them. As a result, there are no standards for composition, quality, or performance. If you have questions about an adjuvant, contact the manufacturer. Companies that produce these products can provide labels, technical data sheets, Safety Data Sheets (SDSs), supplemental labeling, and promotional literature.
Before using any adjuvant, consult the pesticide product label. Some products have very specific adjuvant recommendations or prohibitions. If a label instructs you to use an adjuvant, use the type called for at the directed rate. As noted, many products already contain those adjuvants deemed necessary or useful by the manufacturer or formulator. Adding others may actually decrease efficacy or result in unintended and possibly undesirable effects.
Types of Adjuvants
There are many types of adjuvants. Here are some that are commonly used:
Anti foaming: Anti foaming (defoaming) agents reduce foaming of spray mixtures that may result from using some surfactants and/or from vigorous agitation.
Buffers or pH modifiers: Buffers or pH modifiers allow pesticides to be mixed with diluents or other pesticides of different acidity or alkalinity. Most pesticide solutions or suspensions are stable between pH 5.5 and 7.0 (slightly acidic to neutral). Water outside this range may cause pesticides to degrade very rapidly, in some cases. If you use a buffer, add it to the spray tank water first and mix well. The water must be pH neutral or slightly acidic to start, before adding pesticides or other adjuvants.
Compatibility agents: Compatibility agents help combine pesticides (or pesticides and fertilizers) effectively; reduce or eliminate incompatibility.
Drift control additives: Drift control additives (deposition aids) reduce drift; increase average droplet size and/or lower the number of “fines” (very small droplets) produced.
Emulsifiers: Emulsifiers allow petroleum based pesticides (ECs) to mix with water.
Extenders: Extenders keep pesticides active on a target for an extended period. Some adjuvant manufacturers use this name for stickers.
Invert emulsifiers: Invert emulsifiers allow water based pesticides to mix with petroleum carrier.
Plant penetrants: Plant penetrants allow the pesticide to pass through (penetrate) the outer surface to the inside of treated foliage. Certain plant penetrants may increase penetration on some—but not all—plant species.
Safeners: Safeners reduce the toxicity of a pesticide formulation to the pesticide handler or to the treated surface.
Spreader: Spreader allow pesticide to form a uniform coating layer over the treated surface.
Stickers: Stickers allow pesticide to stay on a treated surface. Some types of stickers increase adhesion of solid particles to a treated surface. This reduces the amount of pesticide that washes off due to rain or irrigation. Others reduce evaporation and/ or slow photo-degradation
Thickeners: Thickeners increase viscosity (thickness) of spray mixtures. Thickeners may reduce drift and/or slow evaporation. (Slowing evaporation is useful when applying systemic pesticides. It increases the time during which the active ingredient can be absorbed by or penetrate plant foliage.)
Wetting agents: Wetting agents allow wettable powders to mix with water.
Surfactants: Some of the most common adjuvants are surfactants (surface active ingredients), which alter the dispersing, spreading, and wetting properties of spray droplets. Examples of surfactants are wetting agents and spreaders. These products physically change the surface tension of a spray droplet. In order to perform well, some pesticide sprays must be able to wet treated foliage thoroughly and evenly. Surfactants that reduce surface tension enable droplets to spread out instead of bead up. This results in better coverage and increases the odds that the pest will contact the pesticide. Surfactants are particularly helpful when treating plants with waxy or hairy leaves
Choosing the Right Adjuvant
Here are some factors to consider when deciding whether to use an adjuvant and how to choose the right one for a particular site and situation.
- Read and follow the label. Is an adjuvant recommended? If so, what type? Do not make substitutions. Note that some product labels may recommend an adjuvant for one type of use or site but prohibit any kind of adjuvant for another labeled use or site. Many end-use formulated products already have adjuvants, and adding adjuvants “on the fly” can decrease efficacy. Suppose, for example, that a certain product is formulated with a wetting agent. If you add another wetting agent when you mix and load a foliar-applied spray, the product may not give better spreading and coverage. Instead, the extra adjuvant may increase runoff, reduce deposition, and even damage the target plant.
- Use only those adjuvants manufactured for agricultural or horticultural uses. Do not use industrial products or household detergents in pesticide spray mixes.
- Remember that no adjuvant is a substitute for good application practices.
- Take adjuvant performance claims “with a grain of salt.” Be skeptical of claims such as “improves root uptake” or “keeps spray equipment clean” unless a reliable source can provide research-based evidence to support them. Only use adjuvant products that have been tested and found effective for your intended use.
- Test spray mixes with adjuvants on a small area before proceeding with full-scale use.