Citrus Industry Magazine CEU 2013 Articles Test Series: Article #4
All about adjuvants
By Stephen H. Futch
Posted Nov. 1, 2013
(expires Oct. 31, 2014)
Adjuvants are products used with pesticides to improve the handling properties of the mixture and/or enhance the pesticide's performance. Used alone, adjuvants do not provide pesticidal activity. Adjuvants may be added to the pesticide when formulated or by the mixer/loader to the spray solution prior to application. Adjuvants may be classified as surfactants, compatibility agents, anti-foaming agents, colorants (dyes), drift control agents and more.
Applicators may use the terms adjuvant and surfactant interchangeably. However, while all surfactants are technically adjuvants, not all adjuvants are surfactants.
The selection of the correct adjuvant is important. The performance of a pesticide can vary depending on the adjuvant selected. Pesticide labels will state if a surfactant is recommended and a suggested rate to be added to the spray mix to maximize pesticide performance.
The term surfactant was originally developed to refer to surface-active agents. Surfactants are products that facilitate and/or improve the emulsifying, dispersing, spreading, wetting or other surface modifying properties of liquids. They are used to produce physical changes in the solution to enhance desired properties of the spray mixture and thus increase the spray coverage on the foliage or aid in the penetration of the solution into the plant.
Surfactants are either water-soluble (hydrophilic) or oil-soluble (lipophilic). Hydrophilic solutions have a strong affinity (natural liking or attraction) for water, whereas lipophilic surfactants have a strong affinity for lipids or oils. The most commonly used surfactants are soaps.
Surfactants are separated into four major groups: anionic, cationic, non-ionic and amphoteric. Anionic and cationic surfactants have electrical charges whereas non-ionic do not have an electrical charge. Amphoteric surfactants may have either a positive or negative charge based upon the pH of the spray solution. The most commonly recommended surfactant is a non-ionic type; however the type selected should vary depending on the pesticide or pesticides chosen.
An emulsion is a mixture of two liquids that are incompletely mixed. Emulsifying agents promote the suspension of one liquid into the other. The two common types of emulsifying agents are oil-in-water or water-in-oil mixtures. The oil-in-water emulsion agents are used to get an oil-soluble pesticide dispersed in a water mixture, thereby allowing it to be sprayed in a water-based solution. When water and oils are mixed, they will form an invert emulsion that creates a thick solution that will resist drift, improve rainfastness or delivery of the product. In some cases, an invert emulsion may be too viscous (thick) to be applied with conventional sprayers. Mayonnaise and butter are two examples of invert (water-in-oil) emulsions in which water is dispersed in vegetable oil or animal fat, respectively.
Wetting agents will decrease the surface tension of the mixture, which allows a larger portion of each spray droplet to contact the surface of the vegetation. Wetting agents increase the coverage of the spray solution, thereby increasing the effectiveness of the pesticide due to increased coverage of the target surface.
CROP OIL CONCENTRATE
Crop oil concentrates are phytobland petroleum or vegetable oils that are formulated to increase the absorption of the pesticide solutions through the cuticle or waxy layer of the leaves. Crop oils contain an emulsifier that aids them in mixing with water. Crop oil concentrates are usually 80 percent to 85 percent petroleum or vegetable oil and 15 percent to 20 percent emulsifier. Product labels will specify if a petroleum or vegetable oil formulation should be used.
Silicone-based surfactants reduce the water surface tension, which allows the water to spread outward onto the leaf surface as compared to beading up on the leaf surface like water on a recently waxed surface. Silicone surfac