Absorption, localisation, translocation and activity of glyphosate in barnyardgrass (Echinochloa crus-galli (L) Beauv):: influence of herbicide and surfactant concentration

The influence of sub-lethal and lethal doses of glyphosate (5 mu g and 10 mu g per plant) applied to the fourth leaf of barnyardgrass (Echinochloa crus-galli) was examined over a treatment period of up to 14 days. Assessments were undertaken on plant growth, chlorophyll fluorescence, absorption and translocation of [C-14]glyphosate. Electronic autoradiography and image analysis were used to examine the distribution of [C-14]glyphosate over the duration of the study. Major sinks affecting glyphosate distribution included the emerging fifth leaf, the roots and 'shoot' (meristem area). At 10 mu g per plant, chlorophyll fluorescence declined over the treatment period; in the source and sink leaves effects were particularly evident at 5 DAT. Absorption and translocation of [C-14]glyphosate (5 and 10 mu g per plant) was rapid during 1-2 DAT, remaining relatively constant thereafter. Approximately 70% of the application was absorbed and, of this, 70% was translocated. The concentration of glyphosate increased in the sinks (the emerging fifth leaf, the roots and shoot (meristem) area) to a maximum at 3 DAT, thereafter declining. This decline was coincident with a decrease (2-3 DAT) in the level of photosynthesis (fluorescence) in the source and sink leaves of plants treated with 10 mu g glyphosate. Incorporation of the surfactant MON 0818 at 0.5, 1.0 or 2.0 ml litre(-1) enhanced herbicidal activity, absorption, translocation and sink accumulation of[C-14]glyphosate (5 mu g per plant), with absorption and translocation greatest at 0.5 mi litre(-1) at 5 DAT. Herbicidal activity at 12-14 DAT, however, was greatest at the 1.0 ml litre(-1) concentration. (C) 2000 Society of Chemical Industry.