FOLIAR ABSORPTION OF SOME GLYPHOSATE FORMULATIONS AND THEIR EFFICACY ON PLANTS

Uptake of various doses (0.27-4.06 g litre(-1)) of glyphosate acid for mulated with various concentrations (0.27-5.42 g litre(-1)) of two pol yethoxylated alcohol surfactants 'Genapol' T-150, 'Genapol' T-250) in wheat (Triticum aestivum L. cv. Ralle) 24 h after application was stud ied. Both surfactants greatly enhanced glyphosate uptake at concentrat ions up to 1.35 g litre(-1). Uptake could be slightly further improved by 'Genapol' T-150 up to 5.42 g litre(-1) while 'Genapol' T-250 at th is high concentration antagonized uptake a little. Uptake of glyphosat e-monoammonium formulated with a quaternary ammonium surfactant ('Trim ao' (8PO)) in wheat and white mustard (Sinapis alba L. cv. Alba) was a lso studied. Uptake of glyphosate-monoammonium in wheat was enhanced a t surfactant concentrations up to 1.35 g litre(-1). Beyond this concen tration uptake continued to increase slightly but not significantly. G enerally, glyphosate-monoammonium formulated with 'Trimao' (8PO) was n ot taken up as extensively by mustard as by wheat, and the optimum sur factant concentration is probably higher on mustard. The optimal combi nations of surfactant concentration and glyphosate dose based on uptak e 24 h after application were used in a time-course study.Results from uptake studies were compared with the efficacy of similar formulation s on wheat. The surfactant concentration range which gave the most pro nounced effect on glyphosate uptake was found to be similar (0-1 g lit re(-1)) in both studies. However, the surfactant concentration providi ng maximum herbicide uptake was found to be higher in the uptake study compared to the surfactant concentration providing optimal efficacy i n the dose-response experiments. A dose rate of 0.5 g litre(-1) of 'Tw een' 20 (sorbitan monolaurate surfactant) improved efficacy of a formu lation with an optimal mix of glyphosate-monoammonium and 'Trimao' (8P O). Ammonium sulfate (5.0 g litre(-1)) did not improve this formulatio n further.