Submitted to: Pest Management Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/23/2006
Publication Date: 9/18/2006
Citation: Shaner, D.L., Belles, D., Westra, P., Brunk, G. 2006. Comparison of efficacy, absorption, and translocation of two glyphosate formulations in velvetleaf (Abutilon theophrasti). Pest Management Science.62:1177-1181 Interpretive Summary: Glyphosate is the most widely used herbicide in the world. It is distributed by a number of agro-chemical companies, each of which has their own formulation. The efficacy of glyphosate is dependent on the surfactants or adjuvants that are included in the formulation. In this study we compared the efficacy of three different formulations of glyphosate on velvetleaf, a weed that is very difficult to control with glyphosate. We found that one of the formulations, which includes 1-aminomethanamide dihydrogen tetraoxsosulfate (AMADS), was superior to the other two formulations of glyphosate. The better activity of the AMADS-containing formulation is due to more rapid uptake and better translocation of glyphosate in velvetleaf. These results demonstrate the effect of different formulations on glyphosate activity and suggest that lower rates of the herbicide can be used with the proper adjuvant.
Technical Abstract: Growth analysis, absorption and translocation studies were conducted to compare an acid formulation of glyphosate with an isopropyl amine formulation. Four to six leaf velvetleaf were treated with 0, 210, 280, 420, 560 and 840 g ae ha-1 of the acid and isopropyl amine formulations. The acid formulation at each application rate reduced velvetleaf biomass more than the isopropyl amine formulation. The GR50 value for the acid formulation was 4 times lower than the GR50 for the isopropyl amine formulation based on a log-logistic regression analysis of velvetleaf dry weight. Absorption of 14C glyphosate into leaves of 4 to 6 leaf velvetleaf was 3.6 times greater (19 vs. 5% of applied) after 6 h when applied as the acid formulation compared to isopropyl amine formulation. Translocation out of the treated leaf of the acid formulation was also greater. After 72 h, 1.6 times more 14C glyphosate applied in the acid formulation had translocated out of the treated leaf compared to the isopropyl amine formulation (22 vs. 14% of applied). The greater efficacy of the glyphosate acid formulation over the isopropyl amine formulation on velvetleaf is probably due to the greater rate of absorption of the herbicide and increased translocation.