Relationship of Leaf Position to Herbicide Absorption and Organosilicone Adjuvant Efficacy

Abstract

The absorption of14C-bentazon and14C-acifluorfen by individual leaves of velvetleaf was measured from the cotyledons to the most recently developed leaf in plants that had developed seven leaves beyond the cotyledons. Herbicide absorption 1 min after application was greatly enhanced by the organosilicone adjuvant Sylgard 309 explaining previously observed enhanced efficacy and rainfastness by this adjuvant.14C-herbicide absorption was greatest by the cotyledons and decreased upward to the most recently developed leaf. Absorption of the14C-Sylgard 309 was similar to that of the14C-labelled herbicides and was not related to the number of stomata or leaf area covered by the spray droplets. These results are consistent with the hypothesis that the mode of action of Sylgard 309 is to enhance cuticular absorption and not stomatal infiltration.