The biological activity of rimsulfuron applied with 33 alcohol ethoxylate surfactants was determined on six economically important weed species. The surfactants had hydrophobes ranging from 6 to 24 carbons and hydrophiles ranging from 3 to 32 ethylene oxides (EOs), and the weeds had different leaf orientations, surface characteristics, and chemical compositions. In general, similar activity was observed among weed species with correlation coefficients ranging from 0.62 to 0.94. A few distinct species-specific differences were identified. For example, increasing surfactant size generally increased rimsulfuron activity on velvetleaf, but activity was reduced on giant foxtail with surfactants having the longest alkyl chain and the highest number of EO units. Increasing surfactant size increased common cocklebur control if the right balance between the hydrophobic and hydrophilic group was maintained. The optimum surfactant type with rimsulfuron across six species from both the empirical and the modeling results ranged from a hydrophobe with 17 carbons and a hydrophilic group with 20 to 30 EOs to 24 carbons and 13 EOs.
Nomenclature: Rimsulfuron; common cocklebur, Xanthium strumarium L. #3 XANST; giant foxtail, Setaria faberi Herrm # SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH.
Additional index words: Adjuvant, nonionic surfactant, species specificity, structure–activity.
Abbreviations: EO, ethylene oxide; HLB, hydrophilic–lipophilic balance.
