Influence of formulation and glyphosate salt on absorption and translocation in three annual weeds

Absorption and translocation of three commercial formulations of glyphosate, the isopropylamine salt formulated as Roundup Ultra™™ (IPA1) and Roundup UltraMax™™ (IPA2) and the diammonium salt formulated as Touchdown™™ IQ (DA), were compared in three- to five-leaf velvetleaf, common waterhemp, and pitted morningglory. Absorption of ¹⁴C-glyphosate in velvetleaf was not significantly different among the three formulations up to 50 h after treatment (HAT). More absorption of ¹⁴C-glyphosate occurred in the IPA1 (26.0%%) vs. the IPA2 (17.7%%) formulation over 74 h. Of the total ¹⁴C-glyphosate absorbed, 20 to 35%% was translocated from the treated leaf to the rest of the plant. Initial absorption of ¹⁴C-glyphosate was rapid in common waterhemp with the IPA1 (42.7%%) and IPA2 (30.7%%) formulations; both were higher compared with absorption of the DA formulation (11.5%%) by 2 HAT. These differences continued up to 26 HAT, but no differences were evident by 74 HAT. Up to 65%% of the ¹⁴C-glyphosate absorbed was translocated out of the treated leaf by 74 HAT, with roots the primary sink. Initial absorption of ¹⁴C-glyphosate was slow in pitted morningglory compared with the other species. More foliar absorption occurred in plants treated with the DA (13.6%%) vs. the IPA2 formulation (4.9%%) by 6 HAT. Absorption beyond 26 HAT was not different among the three glyphosate formulations. Translocation of ¹⁴C-glyphosate to roots was 27%% greater as the DA salt than IPA1 and IPA2 by 74 HAT. The distribution pattern of glyphosate was similar in all species; phosphorimages demonstrated movement both acropetal and basipetal, with accumulation in roots greater than in any other plant parts. An efficacy study parallel to the ¹⁴C study showed no difference among the three glyphosate formulations on the species investigated at both 74 HAT and 2 wk after treatment.Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer AMATA; pitted morningglory, Ipomoea lacunosa L. IPOLA; velvetleaf, Abutilon theophrasti Medicus ABUTH.