Greenhouse studies were conducted to determine the response of common lambsquarters and velvetleaf to glyphosate applied alone or with 20 g L−1 of ammonium sulfate (AMS). Minimal response of common lambsquarters to glyphosate plus AMS was observed. The GR50 values for velvetleaf decreased dramatically from 451 to 92 g ha−1 for glyphosate applied alone and glyphosate plus AMS, respectively. The addition of AMS did not affect foliar absorption of 14C-glyphosate in common lambsquarters but increased absorption in velvetleaf. A twofold increase in translocation, as a percentage of total 14C-glyphosate absorbed, occurred in velvetleaf with the addition of AMS. Increased control of velvetleaf with glyphosate plus AMS may be partially explained by greater glyphosate absorption and translocation. Increased translocation of glyphosate applied with AMS in velvetleaf was an indirect effect of greater foliar uptake as well as greater partitioning of glyphosate out of the treated leaf.
Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL; velvetleaf, Abutilon theophrasti Medicus ABUTH.