Translocation and Absorption of Glyphosate in Flowering Sicklepod (Senna obtusifolia)

Sicklepod is a competitive and prolific weed that emerges throughout the crop season. Glyphosate applications to flowering sicklepod greatly reduce seed production, but there is limited information on glyphosate translocation in flowering weeds. Therefore, a laboratory study was conducted to document the absorption and translocation of 14C-glyhosate in flowering sicklepod. Flowering sicklepod plants were treated with a 14C-glyphosate solution, and 14C-glyphosate absorption and translocation was quantified by scintillation spectrometry. Absorption and translocation of 14C-glyphosate in flowering sicklepod were similar for both 0.21 and 0.42 kg ae ha−1 glyphosate. Although the treated leaflets retained approximately 50% of the recovered 14C-glyphosate, movement of the herbicide was both acropetal and basipetal, with the highest 14C-glyphosate concentrations in the shoot below the treated leaf and the roots. By 96 h after treatment, sicklepod buds and flowers had abscised, but analysis of the structures revealed accumulation of 2% of the recovered 14C-glyphosate. Based on results of the study, effects of glyphosate accumulation in buds and flowers combined with plant stress associated with the primary and secondary effects of glyphosate result in bud and flower abscission, drastically reducing sicklepod seed production.