Comparison of efficacy, absorption and translocation of three glyphosate formulations on velvetleaf (Abutilon theophrasti)

Abstract

Growth analysis, absorption and translocation studies were conducted to compare a 1-aminomethanamide dihydrogen tetraoxosulfate (GLY-A) formulation of glyphosate with two isopropylamine (GLY-IPA-1, GLY-IPA-2) formulations of glyphosate on velvetleaf. The two isopropylamine formulations differed by the presence of a surfactant in the formulation, GLY-IPA-1 containing surfactant whereas GLY-IPA-2 did not. Four- to six-leaf velvetleaf was treated with GLY-A and GLY-IPA-1 and GLY-IPA-2 (0, 50, 67, 89, 119, 158, 280, 420, 560 and 840 g AE ha(-1)) with and without ammonium sulfate (AMS; 20 g L(-1)). GLY-A and GLY-IPA-2 included a non-ionic surfactant (2.5 mL L(-1)) in the spray solution at all herbicide concentrations. No additional surfactant was added to GLY-IPA-1. The IC50 value for GLY-A was 88 g AE ha(-1) compared with 346 and 376 g AE ha(-1) for GLY-IPA-1 and GLY-IPA-2 respectively in the absence of AMS. When AMS (20 g L(-1)) was added to the spray solution, the estimated IC50 values were 143, 76 and 60 g AE ha(-1) for GLY-IPA-1, GLY-IPA-2 and GLY-A respectively. Absorption of 14C-glyphosate into the third leaf of five- to six-leaf velvetleaf was three- to sixfold greater 72 h after treatment (HAT) when applied as GLY-A compared with GLY-IPA-1 and GLY-IPA-2 respectively in the absence of AMS. AMS (20 g L(-1)) increased absorption of 14C-glyphosate in all glyphosate formulations two- to threefold, but differences among the formulations remained. Approximately three- and sixfold more 14C-glyphosate applied as GLY-A had translocated out of the treated leaf compared with GLY-IPA-1 and GLY-IPA-2 respectively by 72 HAT. Adding AMS (20 g L(-1)) increased translocation of 14C-glyphosate out of the treated leaf approximately 2.5-fold for all three formulations. The increased efficacy of GLY-A versus GLY-IPA-1 and GLY-IPA-2 on velvetleaf is due to the greater rate of absorption and subsequent translocation of glyphosate out of the treated leaf. AMS increased the efficacy of all three formulations by increasing absorption and translocation of glyphosate in the plant.

Evaluation of the efficacy of glyphosate plus urea phosphate in the greenhouse and the field

“…Molin et al 21 reported that AMADS caused rapid subcellular and subcuticular damage to cotton leaves. Belles et al 23 suggested that AMADS could increase the glyphosate efficacy by accelerating the initial herbicide absorption. Glyphosate + UPP may increase the efficacy by causing severe cuticle disruption or accelerating the initial herbicide absorption.…”

Comparison of WeatherMax<sup>®</sup> and Engame<sup>TM</sup> Formulations of Glyphosate on Cotyledon Surface Structure, Chlorophyll A Fluorescence and Shikimate Levels in Isogenic Cotton Cultivars Differing in Roundup Resistance

“…Previously, Engame™ was shown to be 2 to 3 times more active than Roundup Ultra, Touchdown or Ultramax formulations of glyphosate in growth inhibition [26] [27]. In addition, absorption of 14 C-glyphosate was three to sixfold greater with glyphosate supplemented with AMADS compared to the glyphosate-isopropylamine formulation [10] and approximately three to sixfold more glyphosate was translocated out of the treated leaf with the AMADS formulation [10]. Similarly, the IC 50 of the glyphosate-AMADS formulation was 3 to 4 times lower than a glyphosate-isopropylamine formulation [10].…”

“…Additives, such as ammonium sulfate, were already known to increase the phytotoxicity of many water-soluble post-emergence herbicides in glyphosate [2] [11] [18]. For example, ammonium sulfate reduced the concentration of glyphosate isopropylamine salt to cause a 50% inhibition of velvetleaf dry weight accumulation by two-to five-fold [10].…”

Determination of Inter-leaf Translocated Free Glyphosate in Arabidopsis thaliana using Liquid Chromatography Tandem Mass Spectrometry (LCMS/MS) after Derivatization with Fluorenylmethyloxycarbonyl Chloride (FMOC-Cl)

“…Analysis of glyphosate translocation in plants using the 14 C analog of the herbicide has been reported in the literature [18,19]. Given the diminishing production of this radio-labeled analog, it is conceivable that this method will soon become inapplicable.…”