Optimizing foliar activity of isoxaflutole on giant foxtail (Setaria faberi) with various adjuvants

Abstract

Greenhouse, laboratory, and field studies were conducted to evaluate the potential of nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), and 28% urea ammonium nitrate (UAN) to enhance whole plant efficacy, absorption, and spray retention of foliar applications of isoxaflutole to giant foxtail. In greenhouse studies, isoxaflutole at 10 g ai ha−1reduced giant foxtail growth 5%, whereas the addition of a spray adjuvant reduced giant foxtail growth at least 75%. The addition of UAN improved giant foxtail growth reduction when used in combination with isoxaflutole plus NIS. Isoxaflutole spray retention on the leaf surface was increased with an adjuvant and a further increase was observed with the addition of UAN. Isoxaflutole applied with NIS, COC, and MSO resulted in 42, 60, and 91%14C absorption, respectively, compared to 21% absorption from isoxaflutole applied alone 24 h after treatment (HAT). Increased14C absorption and entry into the cuticle when an adjuvant was utilized with isoxaflutole resulted in greater translocation of14C from isoxaflutole out of the treated leaf. Significant basipetal movement from foliar applications of14C-isoxaflutole suggests phloem mobility. In field studies, isoxaflutole applied with MSO provided greater giant foxtail growth reduction compared to isoxaflutole applied with NIS and in some cases COC. The addition of UAN to isoxaflutole did not increase whole plant efficacy in field studies. These studies indicate isoxaflutole has excellent potential to be used for control of existing giant foxtail present at the time of corn planting if an adequate adjuvant is utilized.