Chapter 25

Pesticides for Grapevines

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.

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.

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.

Defoaming Agents

Some pesticide formulations create foam or a frothy “head” in spray tanks.

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.

Emulsifiers

Emulsifier agents work by coating tiny particles or groups of the liquid molecules and preventing them from coagulating with other like molecules.

Extenders

Extenders are adjuvants that can extend the useful life of a spray chemical.

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.

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.

Thickeners

Drift control agents are designed to reduce spray drift, which most often results when fine (< 150 µm diameter) spray droplets are carried away from the target areas.

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