Absorption and translocation of glyphosate isopropylamine and trimethylsulfonium salts in Abutilon theophrasti and Setaria faberi

Growth chamber and laboratory experiments were conducted to evaluate foliar absorption and translocation of the isopropylamine (Ipa) or trimethylsulfo nium (Tms) salts of glyphosate in Abutilon theophrasti and Setaria faberi. Glyphosate was applied at 250 g ai ha(-1). Absorption of C-14-glyphosate in both formulations increased similarly in both species over 72 h. Seventy-t wo hours after treatment (HAT), A. theophrasti absorbed 26% of applied C-14 of both formulations, whereas S. faberi absorbed 43% of both formulations. The addition of 1% ammonium sulfate (AMS) to both formulations increased t he amount of herbicide absorbed to 35% in A. theophrasti and 60% in S. fabe ri 72 HAT. Translocation of absorbed C-14-glyphosate in both formulations ( with or without AMS) was greater for S. faberi than A. theophrasti 72 HAT. For A. theophrasti, 17% of C-14 absorbed in Ipa and Tms formulations were t ranslocated out of the treated leaf, whereas additions of AMS increased the amount translocated to 25 and 23% for Ipa and Tms, respectively. The large st portion of translocated C-14 moved to tissues above the treated leaf. Fo r S. faberi, 37% of absorbed C-14 in both Ipa and Tms formulations were tra nslocated out of the treated leaf 72 HAT, whereas 42% translocated when 1% AMS was added to both formulations. In S. faberi, the largest portion of C- 14-glyphosate translocated to tissues below the treated leaf. In summary, n o differences were found between Ipa and Tms formulations in both weed spec ies.