Research was conducted to evaluate structure–function relationships of citric acid esters that varied in alkyl chain number (mono-, di-, and tri-), ethylene oxide number (EO 4,7,9,25,35,52), and alkyl chain length (C8, C12/14, C16/18). Adjuvant efficacy was evaluated on two weed species for each of the four herbicides. The experimental adjuvants were applied with glyphosate and glufosinate on giant foxtail and common lambsquarters, imazamox on velvetleaf and common lambsquarters, and nicosulfuron on giant foxtail and large crabgrass. Adjuvant efficacy was weed and herbicide specific. EO number and alkyl chain length and number influenced adjuvant efficacy with the effectiveness of various combinations dependent on both herbicide and weed species. EO numbers as high as 52 were shown to be effective for glyphosate, glufosinate, and imazamox.
