Adjuvant effects on imazethapyr, 2,4-D and picloram absorption by leafy spurge (Euphorbia esula)

Laboratory experiments were conducted to identify adjuvants that improve absorption of imazethapyr, 2,4-D amine, and picloram by leafy spurge. Adjuvants (0.25% v/v) included crop oil concentrate (COC), methylated seed oil (MSO), nonionic surfactant (NIS), organosilicones (Silwet L-77(R), Sylgard(R) 309, Silwet(R) 408), 3:1 mixtures of acetylinic diol ethoxylates (ADE40, ADE65, ADE85) with Silwet L-77, ammonium sulfate (2.5 kg ha(-1)), and 28% urea ammonium nitrate (UAN, 2.5% v/v). Adjuvants mere combined with C-14-herbicide and commercially formulated herbicide product. Leaves were harvested 2 DAT, rinsed with 10% aqueous methanol to remove surface deposits of herbicide, and dipped in 9:1 hexane:acetone to solubilize cuticular waxes. Imazethapyr absorption increased by 38 to 68% when UAN was combined with COC, NIS, or MSG. Total absorption of inazethapyr plus COC, MSG, or MS exceeded 86% 2 DAT when UAN was added. Urea ammonium nitrate reduced the amount of imazethapyr associated with the cuticular wax by 2.0%. Imazethapyr absorption was similar on both the abaxial and adaxial leaf surface when UAN was not added; however, 12% more imazethapyr was absorbed from the abaxial leaf surface than from the adaxial leaf surface when UAN was combined with Sylgard 309. Uptake of 2,4-D ranged from 54 to 78% and was greatest with Silwet 408 and 3:1 mixture of ADE40:Silwet L-77. Picloram absorption ranged from 3 to 19%. Buffering picloram treatment solutions to pH 7 and including 2.5 kg ha(-1) ammonium sulfate increased picloram absorption to 37%.