ADJUVANT EFFECTS ON IMAZETHAPYR, 2,4-D AND PICLORAM ABSORPTION BY LEAFY SPURGE (EUPHORBIA-ESULA)

Laboratory experiments were conducted to identify adjuvants that impro ve absorption of imazethapyr, 2,4-D amine, and picloram by leafy spurg e. Adjuvants (0.25% v/v) included crop oil concentrate (COC), methylat ed seed oil (MSO), nonionic surfactant (NIS), organosilicones (Silwet L-77(R), Sylgard(R) 309, Silwet(R) 408), 3:1 mixtures of acetylinic di ol ethoxylates (ADE40, ADE65, ADE85) with Silwet L-77, ammonium sulfat e (2.5 kg ha(-1)), and 28% urea ammonium nitrate (UAN, 2.5% v/v). Adju vants mere combined with C-14-herbicide and commercially formulated he rbicide product. Leaves were harvested 2 DAT, rinsed with 10% aqueous methanol to remove surface deposits of herbicide, and dipped in 9:1 he xane:acetone to solubilize cuticular waxes. Imazethapyr absorption inc reased 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 whe n UAN was added. Urea ammonium nitrate reduced the amount of imazethap yr associated with the cuticular wax by 2.0%. Imazethapyr absorption w as similar on both the abaxial and adaxial leaf surface when UAN was n ot 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 greate st with Silwet 408 and 3:1 mixture of ADE40:Silwet L-77. Picloram abso rption 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%.