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Adjuvants

Adjuvants are added to spray mixtures to increase the effectiveness of the main active ingredient. There are many classes of adjuvants, each with its own spectrum of activity. An adjuvant may have more than one mode of action. When the cost of the adjuvant is less than that of the chemical, there may be clear economic advantages in using an adjuvant rather than a high rate of a chemical. For example, the rate of NAA may be reduced 50 percent when a suitable surfactant is added to the spray mixture.

The use of adjuvants with pesticides may significantly enhance their activity. Plant growth regulators are applied to modify plant growth; to be effective they must enter the plant as with other systemic pesticides. This is in contrast to most other pesticide applications, in which a uniform deposit is desired on the outside of the plant. Because leaf exteriors have waxes, cutin, pectin, and cellulose between the chemical and the cell contents, anything we can do to bring about a uniform deposit and penetrate these barriers to uptake must be seriously considered.

The wholesale use of adjuvants with orchard sprays may not be warranted. Many pesticides contain adjuvants to stabilize the product and to make it effective in the spray tank. Thus, growers should be cautious in using adjuvants and should rely on reputable sources of information for data regarding the selection of a suitable adjuvant. See Table 3-6 for a list of adjuvants available from major ag chemical suppliers. Check labels of specific products before using in any application.

Below are different classifications of adjuvants.

Acidifier. Acidifiers are adjuvants that have the ability to reduce the pH of solutions. They are useful when the pH of the spray water is too high. However, because acidifiers can only lower the pH, their indiscriminate use is not recommended. In some cases if the spray water pH is correct or lower than the recommended pH for the chemical in question, then the use of an acidifier can reduce the pesticide's effectiveness.

Antifoaming agent--see "defoamer."

Antitranspirant. Antitranspirants are chemicals that can reduce transpiration in plants. They can be applied as main chemicals or may be used to enhance the activity of other chemicals. Antitranspirants can be effective in transplanting nursery stock, especially when leaves are present and low humidity and/or high winds are expected.

Buffering agent. Buffering agents raise or lower the pH of the spray mixture to the designed pH of that buffering agent. Thus, buffering agents can be useful when the spray water pH is either too high or too low.

The quantity of buffering agent needed in a spray tank may be difficult to determine. Various buffering agents have different powers to buffer. In addition, merely measuring the pH of a spray solution may not give an indication of the quantity of buffering agent needed. For example, sulfuric acid and acetic acid (the acid in vinegar) may both have low pH values. However, sulfuric acid is a much stronger acid than acetic acid, and much more buffering agent would be needed to change the pH of a sulfuric acid solution than an acetic acid solution.

Compatibility agent. Compatibility agents are adjuvants that allow easier mixing of two or more components in a solution. Using compatibility agents may allow the use of two or more chemicals in a tank that would otherwise be incompatible. Crop oil. Crop oils normally contain 95 to 98 percent petroleum oil with 1 to 2 percent added surfactant. Crop oils can be effective as penetrants and as surfactants.

Crop oil concentrate. Crop oil concentrates normally contain between 80 and 85 percent petroleum oil with 15 to 20 percent surfactant. These products can be effective as penetrants and as surfactants.

Defoamer. Defoamers are adjuvants that reduce foaming when there is excessive foam in a spray tank. Excessive foaming can be a significant problem with some agitation systems in sprayers, especially when the water level in a tank gets low enough that a mechanical agitation system would cause excessive foam.

Drift retardant. Drift retardants are used to reduce off-target drift of pesticides and are often used with aerial applications. Since aerial applications normally are made with highly concentrated spray mixtures, spray nozzles that create small droplets are often used. Since small droplets can travel farther than larger droplets, some drift retardants work by increasing mean droplet size.

Extender. 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. Since many pesticides are broken down by ultraviolet light, some extenders have the ability to intercept ultraviolet light.

Organosilicon surfactants are a new class of surfactants. Generally they are more effective per unit of active ingredient than the more traditional surfactants.

Penetrant. Penetrants are adjuvants that help chemicals penetrate plants.

Spreader. Spreaders are surfactants. See "surfactants."

Sticker. Stickers are adjuvants that aid in the attachment of a chemical to a surface. They can lengthen the time that a chemical is attached to a plant surface. Stickers generally make pesticide deposits less easily removed from leaves by forces such as rain or wind.

Sticker-spreader (also spreader-sticker). Sticker-spreaders are compounds that perform two functions at the same time. They stick and spread chemicals to plant surfaces. See "stickers and surfactants" for descriptions of individual types of adjuvants.

Surface active agent. Surface active agents are surfactants. See "surfactants."

Surfactant. Surfactants are adjuvants that reduce the surface tensions of solutions, helping them spread and cover surfaces more effectively. Surfactants are probably the best-known class of adjuvants. Most adjuvants are a double-ended molecule, one end being water soluble and one end being oil soluble. Therefore, these molecules can line up between water-like compounds and oil-like compounds and make them more compatible. Surfactants can be uncharged (nonionic), positively charged (cationic), or negatively charged (anionic).

Suspension agent. Suspension agents aid the suspension of one material in another. These types of adjuvants are often used in liquid fertilizer mixes as well as in liquid pesticide formulations to help maintain a uniform product mix.

Thickener. Thickeners are adjuvants that increase the viscosity of solutions. Calcium dips were proven more effective in increasing fruit calcium levels when a thickener was added to the calcium dipping solution, compared to a water solution.

Vegetable oil concentrate. These adjuvants are similar to crop oil and crop oil concentrates except that vegetable oils are used instead of petroleum oils.

Wetting agent. This is another name for surfactants. See "surfactants."

References and Contacts
A Guide to Agricultural Spray Surfactants used in the United States, 1992. Lori T. Harvey. 244 pages. $17.50. Thomson Publications, P.O. Box 9335, Fresno, CA 93791.

Agricultural Chemicals Label Manual. Rohm and Haas Company, Independence Mall West, Philadelphia, PA 19106-2399 (610-255-0836).

Crop Protection Products, Label & MSDS Book. Loveland Industries, Inc. c/o UAP, P.O. Box 1289, Greeley, CO 80632-1289. Contact Loveland Industries, Inc. (717-656-6098), or local AG-CHEM, Inc., representative.

Kalo Technical Product Materials. Kalo Laboratories, Inc. 4550 W. 109th Street, Suite 250, Overlook Park, KS 66211-1311 (800-255-5196).

Miller specimen labels, Miller Chemical & Fertilizer Corp., P.O. Box 333, Hanover, PA 17331 (717-633-1434).

Riverside Adjuvant Tech. Handbook. Terra International, Inc. 600 Fourth Street, P.O. Box 6000, Sioux City, IA 51102-6000 (800-762-3837).

Setre Chemical Company Product Label Book, 1995. Setre Chemical Company, 6075 Popular Ave., Suite 500, Memphis, TN 38119. Contact local Helena Chemical Co. representative.