Chapter 24

Greenhouse Pesticides

Spray Adjuvants

An adjuvant is a broadly defined as any non-pesticide material added to a pesticide product or pesticide spray mixture to enhance the pesticide’s performance and/or the physical properties of the spray mixture. They are used extensively in products designed for foliar applications. Adjuvants are distinguished by how they are combined with the pesticide. A formulation adjuvant is already included in the pesticide product by the manufacturer. A spray adjuvant is broadly defined as any substance added to the spray tank, separate from a formulation adjuvant that is already included in the pesticide product by the manufacturer. Adjuvants are designed to perform specific functions, including buffering, dispersing, emulsifying, spreading, sticking, and wetting. Adjuvants also can reduce evaporation, foaming, spray drift, and volatilization. No single adjuvant can perform all these functions, but different compatible adjuvants often can be combined to perform multiple functions simultaneously. Because adjuvants lack pesticidal properties, the U.S. Environmental Protection Agency does not register them. As a result, there is no set of standards for composition and quality, although some states have modified registration requirements for these chemicals and may require labels, technical data sheets, and efficacy information. Many registered pesticide products have very specific label recommendations on use with one or more adjuvants. Failure to follow these instructions is as much a violation of the product label as misuse of the pesticide. 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

Much of the confusion surrounding adjuvants can be attributed to the lack of understanding of adjuvant terminology. For example, many people use the terms adjuvant and surfactant interchangeably. These terms can refer to the same product because all surfactants are adjuvants. However, not all adjuvants are surfactants.

Buffers or pH Modifiers

Most pesticide solutions or suspensions are stable between pH 5.5 and pH 7.0 (slightly acidic to neutral). Consequently, the pH plays a large role in pesticide efficacy.

Conditioning Agents

Conditioning or water-softening agents reduce problems associated with hard water. Hard water minerals, especially calcium and magnesium ions, bind with active ingredients of some pesticides, which results in decreased pesticide performance.

Compatibility Agents

Pesticides are commonly combined with liquid fertilizers or other pesticides. Certain combinations can be physically or chemically incompatible, which causes clumps and uneven distribution in the tank. Occasionally the incompatible mixture plugs the pump and distribution lines resulting in expensive cleanup and repairs.

Defoaming Agents

Some pesticide formulations create foam or a frothy “head” in spray tanks. Excessive foaming can be a significant problem with some agitation systems.

Drift Control Additives

Drift is a function of droplet size. Small, fine drops with diameters of 100 microns or less tend to drift away from targeted areas. Drift control additives, also known as deposition aids, improve on-target placement of the pesticide spray by increasing the average droplet size.

Emulsifiers

Emulsifier agents work by coating tiny particles or groups of the liquid molecules and preventing them from coagulating with other like molecules. The emulsifiers allow oil and water solutions to mix.

Extenders

Extenders are adjuvants that can extend the useful life of a spray chemical. They work by increasing the chemical’s adhesion to the leaf, by reducing any factor that can diminish chemical effectiveness, or by enhancing chemical weatherability.

Safeners

Safeners—reduce the toxicity of a pesticide formulation to the pesticide handler or to the treated surface.

Stickers

A sticker is an adjuvant that used for increasing the viscoelasticity and adhesiveness of pesticide formulations. They are used to increase the retention of a liquid spray applied to plants and to reduce the sensitivity of the deposit to environmental weathering, especially rainfall. Within this latter context, they are often referred to as extenders because they extend the period of time for which the active ingredient is toxic.

Surfactants

Surfactants are the most widely used and probably the most important of all adjuvants. Surfactants, also called wetting agents, spreaders, and penetrants, physically alter the surface tension of a spray droplet. These products physically change the surface tension of a spray droplet. The surfactant acts by reducing the surface tension of the water on the surface of the spray drop and by reducing the interfacil tension between the spray drop and surface of the leaf. Surfactants that reduce surface tension enable droplets to spread out instead of bead up.

Thickeners

Thickeners are used to reduce drift of sprays. These products not only help volatile pesticides become less volatile, they also cause the carrier solution to become more viscous and heavier. This is beneficial when spraying an outdoor production area near a housing subdivision. It reduces drift, odor, and waste.

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