Growth chamber and laboratory experiments were conducted to evaluate foliar absorption and translocation of the isopropylamine (Ipa) or trimethylsulfonium (Tms) salts of glyphosate in Abutilon theophrasti and Setaria faberi. Glyphosate was applied at 250 g ai ha⁻¹. Absorption of ¹⁴C-glyphosate in both formulations increased similarly in both species over 72 h. Seventy-two hours after treatment (HAT), A. theophrasti absorbed 26% of applied ¹⁴C of both formulations, whereas S. faberi absorbed 43% of both formulations. The addition of 1% ammonium sulfate (AMS) to both formulations increased the amount of herbicide absorbed to 35% in A. theophrasti and 60% in S. faberi 72 HAT. Translocation of absorbed ¹⁴C-glyphosate in both formulations (with or without AMS) was greater for S. faberi than A. theophrasti 72 HAT. For A. theophrasti, 17% of ¹⁴C absorbed in Ipa and Tms formulations were translocated out of the treated leaf, whereas additions of AMS increased the amount translocated to 25 and 23% for Ipa and Tms, respectively. The largest portion of translocated ¹⁴C moved to tissues above the treated leaf. For S. faberi, 37% of absorbed ¹⁴C in both Ipa and Tms formulations were translocated 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 ¹⁴C-glyphosate translocated to tissues below the treated leaf. In summary, no differences were found between Ipa and Tms formulations in both weed species.

Nomenclature: Glyphosate; Abutilon theophrasti Medic. ABUTH, velvetleaf; Setaria faberi Hermm. SETFA, giant foxtail.