Abstract: Utility adjuvants are adjuvants that are tank-mixed in the spray solution to improve the spray application process, but do not directly influence herbicide efficacy. However, by improving the spray application process, utility adjuvants can indirectly improve herbicide efficacy. There are five primary utility adjuvant types: compatibility agents, deposition agents, drift control agents (sometimes referred to as antidrift agents or drift retardants), defoaming agents, and water conditioning agents, and three secondary utility adjuvant types: acidifying agents, buffering agents, and colorants (dye markers). Herbicides can react either physically or chemically with other spray mixture components to form an unsprayable mixture. Compatibility agents prevent these reactions from occurring. Drift control agents and deposition agents increase the amount of herbicide deposited on target surfaces. The primary function of drift control agents is to reduce the amount of spray solution that moves off-target. Indirectly, the amount of herbicide reaching target surfaces can be increased. A defoaming agent will reduce or prevent foam produced in the spray mixture. Ions in the spray solution can interact with various herbicides, decreasing efficacy. Water conditioning agents will counteract the effect of the ions on herbicides. Water conditioning agents must be added before the herbicide to prevent herbicide–ion interaction. Acidifying and buffering agents function in a similar fashion, reducing or increasing spray solution pH. A buffering agent will maintain a pH range, whereas an acidifying agent will not. Colorants are dyes that are added to the spray solution to produce a visible color on the sprayed area to assist the applicator in applying the herbicide.

Abbreviations: ASTM, American Society for Testing and Materials; DCA, direct control agent; DUE, deposits per unit emission; EO-PO, ethylene oxide–propylene oxide block copolymers; EO-POD, EO-PO ethylenediamines; MW, moleculare weight; PVA, polyvinly alcohol; VMD, volume median diameter; WCA, water conditioning agent.