Abstract: An adjuvant is a material added to a tank mix to aid or modify the action of an agrichemical, or the physical properties of the mixture. For the most recent decade, responsible researchers, suppliers, and trade organizations have made significant progress to identify, understand, and standardize adjuvants. Adjuvant components, their purpose in application, terminology, and now, even tests that establish minimum performance expectations are under development. Certification of voluntary adjuvant composition and performance standards will soon be available. The adjuvant industry has grown into respectability. This paper will attempt to serve as a useful reference for current terminology and definitions accepted by weed science, and also provide a brief discussion of the chemistry favored in current adjuvant compositions.

Additional index words: Surfactant, crop oil, activator, wetting agent.

Abbreviations: ASTM, American Society for Testing and Materials; CMC, critical micelle concentration; CPDA, Chemical Producers and Distributors Association; DST, dynamic surface tension; EST, equilibrium surface tension; HLB, hydrophile–lipophile balance; WSSA, Weed Science Society of America.