Chapter 24

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. Adjuvants are distinguished by how they are combined with the pesticide. A formulation adjuvant is already included in the pesticide product by the manufacturer.

Activator Adjuvants

The primary purpose of activator adjuvants is to enhance the “activity” of the pesticide product. These enhancements—both physical and chemical—generally lead to improved absorption and, as a result, a more efficient use of the pesticide. Activator adjuvants include surfactants, oils, and nitrogen-based fertilizers.

Surfactants

Surfactants are the most widely used and probably the most important of all adjuvants. Surfactants, also called wetting agents and spreaders, physically alter 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.

Oils

Oil adjuvants can increase the penetration of oil-soluble herbicides into plants, and are commonly used when conditions are hot and dry, and/or when leaf cuticles are thick.

Nitrogen-based Fertilizers

Ammonium, or nitrogen, fertilizers are often added to pesticide mixes, where the addition of fertilizer works to both enhance pesticide effects as well as to stimulate the plant growth.

Special Purpose/Utility Adjuvants

Special purpose adjuvants are commonly used to modify the spray solution or application conditions so that a formulation can function effectively. By themselves, they do not directly enhance pesticide activity. These adjuvants include compatibility agents, buffering agents, conditioning agents, defoaming agents, deposition agents, extenders, drift control agents, and extenders. There is some overlap of these functional categories.

Compatibility Agents

Pesticides are commonly combined with liquid fertilizers or other pesticides.

Buffering Agents

Most pesticide solutions or suspensions are stable between pH 5.5 and pH 7.0 (slightly acidic to neutral).

Conditioning Agents

Conditioning or water-softening agents reduce problems associated with hard water.

Defoaming Agents

Some formulations will create foam in some spray tanks.

Deposition Agents

These adjuvants often referred to as “stickers,” used for increasing the viscoelasticity and adhesiveness of pesticide formulations.

Extenders

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

Drift Control Agents

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.

Thickeners

Thickeners, as the name suggests, increase the viscosity of spray mixtures. These adjuvants are used to control drift or slow evaporation after the spray has been deposited on the target area.

Government Regulation of Adjuvants

The U.S. Environmental Protection Agency (EPA) regulates the inclusion of certain ingredients in adjuvant formulations, but it does not stringently test and regulate the manufacture and use of adjuvant products (as they do for other pesticides).

Pesticide Labels

Most pesticide labels specify the type of adjuvant to use for best control, but there are many different brands of most types of adjuvants to select from and few sources of good information regarding their relative performance under different conditions.

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