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

Abstract

The influence of sub-lethal and lethal doses of glyphosate (5 µg and 10 µg 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 [14C]glyphosate. Electronic autoradiography and image analysis were used to examine the distribution of [14C]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 µg 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 [14C]glyphosate (5 and 10 µg 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 µg 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 [14C]glyphosate (5 µg per plant), with absorption and translocation greatest at 0.5 ml litre−1 at 5 DAT. Herbicidal activity at 12–14 DAT, however, was greatest at the 1.0 ml litre−1 concentration. © 2000 Society of Chemical Industry